Merge pull request #1170 from lightpanda-io/nikneym/ada-in-web-apis

Use ada-url for URL operations in web APIs

.github/actions/install/action.yml

@@ -5,7 +5,7 @@ inputs:
   zig:
     description: 'Zig version to install'
     required: false
-    default: '0.15.1'
+    default: '0.15.2'
   arch:
     description: 'CPU arch used to select the v8 lib'
     required: false
@@ -17,7 +17,7 @@ inputs:
   zig-v8:
     description: 'zig v8 version to install'
     required: false
-    default: 'v0.1.30'
+    default: 'v0.1.33'
   v8:
     description: 'v8 version to install'
     required: false

.github/workflows/wpt.yml

@@ -31,7 +31,7 @@ jobs:
       - uses: ./.github/actions/install
 
       - name: json output
-        run: zig build -Doptimize=ReleaseFast wpt -- --json > wpt.json
+        run: zig build wpt -- --json > wpt.json
 
       - name: write commit
         run: |

.github/workflows/zig-fmt.yml

@@ -1,7 +1,7 @@
 name: zig-fmt
 
 env:
-  ZIG_VERSION: 0.15.1
+  ZIG_VERSION: 0.15.2
 
 on:
   pull_request:

.gitmodules

@@ -31,3 +31,6 @@
 [submodule "vendor/curl"]
 	path = vendor/curl
 	url = https://github.com/curl/curl.git
+[submodule "vendor/brotli"]
+	path = vendor/brotli
+	url = https://github.com/google/brotli

Dockerfile

@@ -1,10 +1,10 @@
 FROM debian:stable
 
 ARG MINISIG=0.12
-ARG ZIG=0.15.1
+ARG ZIG=0.15.2
 ARG ZIG_MINISIG=RWSGOq2NVecA2UPNdBUZykf1CCb147pkmdtYxgb3Ti+JO/wCYvhbAb/U
 ARG V8=14.0.365.4
-ARG ZIG_V8=v0.1.30
+ARG ZIG_V8=v0.1.33
 ARG TARGETPLATFORM
 
 RUN apt-get update -yq && \

Makefile

@@ -96,9 +96,16 @@ wpt-summary:
 	@printf "\e[36mBuilding wpt...\e[0m\n"
 	@$(ZIG) build wpt -- --summary $(filter-out $@,$(MAKECMDGOALS)) || (printf "\e[33mBuild ERROR\e[0m\n"; exit 1;)
 
-## Test
+## Test - `grep` is used to filter out the huge compile command on build
+ifeq ($(OS), macos)
 test:
-	@TEST_FILTER='${F}' $(ZIG) build test -freference-trace --summary all
+	@script -q /dev/null sh -c 'TEST_FILTER="${F}" $(ZIG) build test -freference-trace --summary all' 2>&1 \
+		| grep --line-buffered -v "^/.*zig test -freference-trace"
+else
+test:
+	@script -qec 'TEST_FILTER="${F}" $(ZIG) build test -freference-trace --summary all' /dev/null 2>&1 \
+		| grep --line-buffered -v "^/.*zig test -freference-trace"
+endif
 
 ## Run demo/runner end to end tests
 end2end:

README.md

@@ -164,7 +164,7 @@ You can also follow the progress of our Javascript support in our dedicated [zig
 
 ### Prerequisites
 
-Lightpanda is written with [Zig](https://ziglang.org/) `0.15.1`. You have to
+Lightpanda is written with [Zig](https://ziglang.org/) `0.15.2`. You have to
 install it with the right version in order to build the project.
 
 Lightpanda also depends on

build.zig

@@ -23,7 +23,7 @@ const Build = std.Build;
 
 /// Do not rename this constant. It is scanned by some scripts to determine
 /// which zig version to install.
-const recommended_zig_version = "0.15.1";
+const recommended_zig_version = "0.15.2";
 
 pub fn build(b: *Build) !void {
     switch (comptime builtin.zig_version.order(std.SemanticVersion.parse(recommended_zig_version) catch unreachable)) {
@@ -245,6 +245,7 @@ fn addDependencies(b: *Build, mod: *Build.Module, opts: *Build.Step.Options) !vo
             mod.addCMacro("HAVE_ASSERT_H", "1");
             mod.addCMacro("HAVE_BASENAME", "1");
             mod.addCMacro("HAVE_BOOL_T", "1");
+            mod.addCMacro("HAVE_BROTLI", "1");
             mod.addCMacro("HAVE_BUILTIN_AVAILABLE", "1");
             mod.addCMacro("HAVE_CLOCK_GETTIME_MONOTONIC", "1");
             mod.addCMacro("HAVE_DLFCN_H", "1");
@@ -379,9 +380,11 @@ fn addDependencies(b: *Build, mod: *Build.Module, opts: *Build.Step.Options) !vo
         }
 
         try buildZlib(b, mod);
+        try buildBrotli(b, mod);
         try buildMbedtls(b, mod);
         try buildNghttp2(b, mod);
         try buildCurl(b, mod);
+        try buildAda(b, mod);
 
         switch (target.result.os.tag) {
             .macos => {
@@ -484,6 +487,30 @@ fn buildZlib(b: *Build, m: *Build.Module) !void {
     } });
 }
 
+fn buildBrotli(b: *Build, m: *Build.Module) !void {
+    const brotli = b.addLibrary(.{
+        .name = "brotli",
+        .root_module = m,
+    });
+
+    const root = "vendor/brotli/c/";
+    brotli.addIncludePath(b.path(root ++ "include"));
+    brotli.addCSourceFiles(.{ .flags = &.{}, .files = &.{
+        root ++ "common/constants.c",
+        root ++ "common/context.c",
+        root ++ "common/dictionary.c",
+        root ++ "common/platform.c",
+        root ++ "common/shared_dictionary.c",
+        root ++ "common/transform.c",
+        root ++ "dec/bit_reader.c",
+        root ++ "dec/decode.c",
+        root ++ "dec/huffman.c",
+        root ++ "dec/prefix.c",
+        root ++ "dec/state.c",
+        root ++ "dec/static_init.c",
+    } });
+}
+
 fn buildMbedtls(b: *Build, m: *Build.Module) !void {
     const mbedtls = b.addLibrary(.{
         .name = "mbedtls",
@@ -823,3 +850,34 @@ fn buildCurl(b: *Build, m: *Build.Module) !void {
         },
     });
 }
+
+pub fn buildAda(b: *Build, m: *Build.Module) !void {
+    const ada_dep = b.dependency("ada-singleheader", .{});
+
+    const ada_mod = b.createModule(.{
+        .root_source_file = b.path("vendor/ada/root.zig"),
+    });
+
+    const ada_lib = b.addLibrary(.{
+        .name = "ada",
+        .root_module = b.createModule(.{
+            .link_libcpp = true,
+            .target = m.resolved_target,
+            .optimize = m.optimize,
+        }),
+        .linkage = .static,
+    });
+
+    ada_lib.addCSourceFile(.{
+        .file = ada_dep.path("ada.cpp"),
+        .flags = &.{ "-std=c++20", "-O3" },
+        .language = .cpp,
+    });
+
+    ada_lib.installHeader(ada_dep.path("ada_c.h"), "ada_c.h");
+
+    // Link the library to ada module.
+    ada_mod.linkLibrary(ada_lib);
+    // Expose ada module to main module.
+    m.addImport("ada", ada_mod);
+}

build.zig.zon

@@ -5,9 +5,13 @@
     .fingerprint = 0xda130f3af836cea0,
     .dependencies = .{
         .v8 = .{
-            .url = "https://github.com/lightpanda-io/zig-v8-fork/archive/7177ee1ae267a44751a0e7e012e257177699a375.tar.gz",
-            .hash = "v8-0.0.0-xddH63TCAwC1D1hEiOtbEnLBbtz9ZPHrdiGWLcBcYQB7",
+            .url = "https://github.com/lightpanda-io/zig-v8-fork/archive/305bb3706716d32d59b2ffa674731556caa1002b.tar.gz",
+            .hash = "v8-0.0.0-xddH63bVAwBSEobaUok9J0er1FqsvEujCDDVy6ItqKQ5",
+        },
+        //.v8 = .{ .path = "../zig-v8-fork" }
+        .@"ada-singleheader" = .{
+            .url = "https://github.com/ada-url/ada/releases/download/v3.3.0/singleheader.zip",
+            .hash = "N-V-__8AAPmhFAAw64ALjlzd5YMtzpSrmZ6KymsT84BKfB4s",
         },
-        // .v8 = .{ .path = "../zig-v8-fork" }
     },
 }

flake.lock

@@ -75,11 +75,11 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1756822655,
-        "narHash": "sha256-xQAk8xLy7srAkR5NMZFsQFioL02iTHuuEIs3ohGpgdk=",
+        "lastModified": 1760968520,
+        "narHash": "sha256-EjGslHDzCBKOVr+dnDB1CAD7wiQSHfUt3suOpFj9O1Q=",
         "owner": "nixos",
         "repo": "nixpkgs",
-        "rev": "4bdac60bfe32c41103ae500ddf894c258291dd61",
+        "rev": "e755547441a0413942a37692f7bf7fc6315bb7f6",
         "type": "github"
       },
       "original": {
@@ -136,11 +136,11 @@
         ]
       },
       "locked": {
-        "lastModified": 1756555914,
-        "narHash": "sha256-7yoSPIVEuL+3Wzf6e7NHuW3zmruHizRrYhGerjRHTLI=",
+        "lastModified": 1760747435,
+        "narHash": "sha256-wNB/W3x+or4mdNxFPNOH5/WFckNpKgFRZk7OnOsLtm0=",
         "owner": "mitchellh",
         "repo": "zig-overlay",
-        "rev": "d0df3a2fd0f11134409d6d5ea0e510e5e477f7d6",
+        "rev": "d0f239b887b1ac736c0f3dde91bf5bf2ecf3a420",
         "type": "github"
       },
       "original": {

flake.nix

@@ -49,7 +49,7 @@
           targetPkgs =
             pkgs: with pkgs; [
               # Build Tools
-              zigpkgs."0.15.1"
+              zigpkgs."0.15.2"
               zls
               python3
               pkg-config

src/app.zig

@@ -4,7 +4,7 @@ const Allocator = std.mem.Allocator;
 
 const log = @import("log.zig");
 const Http = @import("http/Http.zig");
-const Platform = @import("runtime/js.zig").Platform;
+const Platform = @import("browser/js/Platform.zig");
 
 const Telemetry = @import("telemetry/telemetry.zig").Telemetry;
 const Notification = @import("notification.zig").Notification;
@@ -36,6 +36,7 @@ pub const App = struct {
         http_connect_timeout_ms: ?u31 = null,
         http_max_host_open: ?u8 = null,
         http_max_concurrent: ?u8 = null,
+        user_agent: [:0]const u8,
     };
 
     pub fn init(allocator: Allocator, config: Config) !*App {
@@ -53,6 +54,7 @@ pub const App = struct {
             .http_proxy = config.http_proxy,
             .tls_verify_host = config.tls_verify_host,
             .proxy_bearer_token = config.proxy_bearer_token,
+            .user_agent = config.user_agent,
         });
         errdefer http.deinit();
 

src/browser/Scheduler.zig

@@ -17,7 +17,6 @@
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 const std = @import("std");
-const log = @import("../log.zig");
 const Allocator = std.mem.Allocator;
 
 const Scheduler = @This();
@@ -38,8 +37,10 @@ pub fn init(allocator: Allocator) Scheduler {
 }
 
 pub fn reset(self: *Scheduler) void {
-    self.high_priority.clearRetainingCapacity();
-    self.low_priority.clearRetainingCapacity();
+    // Our allocator is the page arena, it's been reset. We cannot use
+    // clearAndRetainCapacity, since that space is no longer ours
+    self.high_priority.clearAndFree();
+    self.low_priority.clearAndFree();
 }
 
 const AddOpts = struct {

src/browser/ScriptManager.zig

@@ -18,10 +18,10 @@
 
 const std = @import("std");
 
+const js = @import("js/js.zig");
 const log = @import("../log.zig");
 const parser = @import("netsurf.zig");
 
-const Env = @import("env.zig").Env;
 const Page = @import("page.zig").Page;
 const DataURI = @import("DataURI.zig");
 const Http = @import("../http/Http.zig");
@@ -38,9 +38,6 @@ page: *Page,
 // used to prevent recursive evalutaion
 is_evaluating: bool,
 
-// used to prevent executing scripts while we're doing a blocking load
-is_blocking: bool = false,
-
 // Only once this is true can deferred scripts be run
 static_scripts_done: bool,
 
@@ -48,12 +45,6 @@ static_scripts_done: bool,
 // on shutdown/abort, we need to cleanup any pending ones.
 asyncs: OrderList,
 
-// When an async script is ready to be evaluated, it's moved from asyncs to
-// this list. You might think we can evaluate an async script as soon as it's
-// done, but we can only evaluate scripts when `is_blocking == false`. So this
-// becomes a list of scripts to execute on the next evaluate().
-asyncs_ready: OrderList,
-
 // Normal scripts (non-deferred & non-async). These must be executed in order
 scripts: OrderList,
 
@@ -67,6 +58,22 @@ client: *Http.Client,
 allocator: Allocator,
 buffer_pool: BufferPool,
 script_pool: std.heap.MemoryPool(PendingScript),
+sync_module_pool: std.heap.MemoryPool(SyncModule),
+async_module_pool: std.heap.MemoryPool(AsyncModule),
+
+// We can download multiple sync modules in parallel, but we want to process
+// then in order. We can't use an OrderList, like the other script types,
+// because the order we load them might not be the order we want to process
+// them in (I'm not sure this is true, but as far as I can tell, v8 doesn't
+// make any guarantees about the list of sub-module dependencies it gives us
+// So this is more like a cache. When a SyncModule is complete, it's put here
+// and can be requested as needed.
+sync_modules: std.StringHashMapUnmanaged(*SyncModule),
+
+// Mapping between module specifier and resolution.
+// see https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Elements/script/type/importmap
+// importmap contains resolved urls.
+importmap: std.StringHashMapUnmanaged([:0]const u8),
 
 const OrderList = std.DoublyLinkedList;
 
@@ -78,27 +85,51 @@ pub fn init(browser: *Browser, page: *Page) ScriptManager {
         .asyncs = .{},
         .scripts = .{},
         .deferreds = .{},
-        .asyncs_ready = .{},
+        .importmap = .empty,
+        .sync_modules = .empty,
         .is_evaluating = false,
         .allocator = allocator,
         .client = browser.http_client,
         .static_scripts_done = false,
         .buffer_pool = BufferPool.init(allocator, 5),
         .script_pool = std.heap.MemoryPool(PendingScript).init(allocator),
+        .sync_module_pool = std.heap.MemoryPool(SyncModule).init(allocator),
+        .async_module_pool = std.heap.MemoryPool(AsyncModule).init(allocator),
     };
 }
 
 pub fn deinit(self: *ScriptManager) void {
     self.reset();
+    var it = self.sync_modules.valueIterator();
+    while (it.next()) |value_ptr| {
+        value_ptr.*.buffer.deinit(self.allocator);
+        self.sync_module_pool.destroy(value_ptr.*);
+    }
+
     self.buffer_pool.deinit();
     self.script_pool.deinit();
+    self.sync_module_pool.deinit();
+    self.async_module_pool.deinit();
+
+    self.sync_modules.deinit(self.allocator);
+    // we don't deinit self.importmap b/c we use the page's arena for its
+    // allocations.
 }
 
 pub fn reset(self: *ScriptManager) void {
+    var it = self.sync_modules.valueIterator();
+    while (it.next()) |value_ptr| {
+        value_ptr.*.buffer.deinit(self.allocator);
+        self.sync_module_pool.destroy(value_ptr.*);
+    }
+    self.sync_modules.clearRetainingCapacity();
+    // Our allocator is the page arena, it's been reset. We cannot use
+    // clearAndRetainCapacity, since that space is no longer ours
+    self.importmap = .empty;
+
     self.clearList(&self.asyncs);
     self.clearList(&self.scripts);
     self.clearList(&self.deferreds);
-    self.clearList(&self.asyncs_ready);
     self.static_scripts_done = false;
 }
 
@@ -111,7 +142,7 @@ fn clearList(_: *const ScriptManager, list: *OrderList) void {
     std.debug.assert(list.first == null);
 }
 
-pub fn addFromElement(self: *ScriptManager, element: *parser.Element) !void {
+pub fn addFromElement(self: *ScriptManager, element: *parser.Element, comptime ctx: []const u8) !void {
     if (try parser.elementGetAttribute(element, "nomodule") != null) {
         // these scripts should only be loaded if we don't support modules
         // but since we do support modules, we can just skip them.
@@ -144,6 +175,9 @@ pub fn addFromElement(self: *ScriptManager, element: *parser.Element) !void {
         if (std.ascii.eqlIgnoreCase(script_type, "module")) {
             break :blk .module;
         }
+        if (std.ascii.eqlIgnoreCase(script_type, "importmap")) {
+            break :blk .importmap;
+        }
 
         // "type" could be anything, but only the above are ones we need to process.
         // Common other ones are application/json, application/ld+json, text/template
@@ -157,11 +191,12 @@ pub fn addFromElement(self: *ScriptManager, element: *parser.Element) !void {
     if (try parser.elementGetAttribute(element, "src")) |src| {
         if (try DataURI.parse(page.arena, src)) |data_uri| {
             source = .{ .@"inline" = data_uri };
+        } else {
+            remote_url = try URL.stitch(page.arena, src, page.url.raw, .{ .null_terminated = true });
+            source = .{ .remote = .{} };
         }
-        remote_url = try URL.stitch(page.arena, src, page.url.raw, .{ .null_terminated = true });
-        source = .{ .remote = .{} };
     } else {
-        const inline_source = try parser.nodeTextContent(@ptrCast(element)) orelse return;
+        const inline_source = parser.nodeTextContent(@ptrCast(element)) orelse return;
         source = .{ .@"inline" = inline_source };
     }
 
@@ -177,7 +212,7 @@ pub fn addFromElement(self: *ScriptManager, element: *parser.Element) !void {
     if (source == .@"inline" and self.scripts.first == null) {
         // inline script with no pending scripts, execute it immediately.
         // (if there is a pending script, then we cannot execute this immediately
-        // as it needs to best executed in order)
+        // as it needs to be executed in order)
         return script.eval(page);
     }
 
@@ -198,14 +233,18 @@ pub fn addFromElement(self: *ScriptManager, element: *parser.Element) !void {
         self.scripts.append(&pending_script.node);
         return;
     } else {
-        log.debug(.http, "script queue", .{ .url = remote_url.? });
+        log.debug(.http, "script queue", .{
+            .ctx = ctx,
+            .url = remote_url.?,
+            .stack = page.js.stackTrace() catch "???",
+        });
     }
 
     pending_script.getList().append(&pending_script.node);
 
     errdefer pending_script.deinit();
 
-    var headers = try Http.Headers.init();
+    var headers = try self.client.newHeaders();
     try page.requestCookie(.{}).headersForRequest(page.arena, remote_url.?, &headers);
 
     try self.client.request(.{
@@ -223,88 +262,144 @@ pub fn addFromElement(self: *ScriptManager, element: *parser.Element) !void {
     });
 }
 
-// @TODO: Improving this would have the simplest biggest performance improvement
-// for most sites.
-//
-// For JS imports (both static and dynamic), we currently block to get the
-// result (the content of the file).
-//
-// For static imports, this is necessary, since v8 is expecting the compiled module
-// as part of the function return. (we should try to pre-load the JavaScript
-// source via module.GetModuleRequests(), but that's for a later time).
-//
-// For dynamic dynamic imports, this is not strictly necessary since the v8
-// call returns a Promise; we could make this a normal get call, associated with
-// the promise, and when done, resolve the promise.
-//
-// In both cases, for now at least, we just issue a "blocking" request. We block
-// by ticking the http client until the script is complete.
-//
-// This uses the client.blockingRequest call which has a dedicated handle for
-// these blocking requests. Because they are blocking, we're guaranteed to have
-// only 1 at a time, thus the 1 reserved handle.
-//
-// You almost don't need the http client's blocking handle. In most cases, you
-// should always have 1 free handle whenever you get here, because we always
-// release the handle before executing the doneCallback. So, if a module does:
-//    import * as x from 'blah'
-// And we need to load 'blah', there should always be 1 free handle - the handle
-// of the http GET we just completed before executing the module.
-// The exception to this, and the reason we need a special blocking handle, is
-// for inline modules within the HTML page itself:
-//    <script type=module>import ....</script>
-// Unlike external modules which can only ever be executed after releasing an
-// http handle, these are executed without there necessarily being a free handle.
-// Thus, Http/Client.zig maintains a dedicated handle for these calls.
-pub fn blockingGet(self: *ScriptManager, url: [:0]const u8) !BlockingResult {
-    std.debug.assert(self.is_blocking == false);
-
-    self.is_blocking = true;
-    defer {
-        self.is_blocking = false;
-
-        // we blocked evaluation while loading this script, there could be
-        // scripts ready to process.
-        self.evaluate();
+// Resolve a module specifier to an valid URL.
+pub fn resolveSpecifier(self: *ScriptManager, arena: Allocator, specifier: []const u8, base: []const u8) ![:0]const u8 {
+    // If the specifier is mapped in the importmap, return the pre-resolved value.
+    if (self.importmap.get(specifier)) |s| {
+        return s;
     }
 
-    var blocking = Blocking{
-        .allocator = self.allocator,
-        .buffer_pool = &self.buffer_pool,
-    };
+    return URL.stitch(
+        arena,
+        specifier,
+        base,
+        .{ .alloc = .if_needed, .null_terminated = true },
+    );
+}
 
-    var headers = try Http.Headers.init();
+pub fn getModule(self: *ScriptManager, url: [:0]const u8, referrer: []const u8) !void {
+    const gop = try self.sync_modules.getOrPut(self.allocator, url);
+    if (gop.found_existing) {
+        // already requested
+        return;
+    }
+    errdefer _ = self.sync_modules.remove(url);
+
+    const sync = try self.sync_module_pool.create();
+    errdefer self.sync_module_pool.destroy(sync);
+
+    sync.* = .{ .manager = self };
+    gop.value_ptr.* = sync;
+
+    var headers = try self.client.newHeaders();
     try self.page.requestCookie(.{}).headersForRequest(self.page.arena, url, &headers);
 
+    log.debug(.http, "script queue", .{
+        .url = url,
+        .ctx = "module",
+        .referrer = referrer,
+        .stack = self.page.js.stackTrace() catch "???",
+    });
+
+    try self.client.request(.{
+        .url = url,
+        .ctx = sync,
+        .method = .GET,
+        .headers = headers,
+        .cookie_jar = self.page.cookie_jar,
+        .resource_type = .script,
+        .start_callback = if (log.enabled(.http, .debug)) SyncModule.startCallback else null,
+        .header_callback = SyncModule.headerCallback,
+        .data_callback = SyncModule.dataCallback,
+        .done_callback = SyncModule.doneCallback,
+        .error_callback = SyncModule.errorCallback,
+    });
+}
+
+pub fn waitForModule(self: *ScriptManager, url: [:0]const u8) !GetResult {
+    // Normally it's dangerous to hold on to map pointers. But here, the map
+    // can't change. It's possible that by calling `tick`, other entries within
+    // the map will have their value change, but the map itself is immutable
+    // during this tick.
+    const entry = self.sync_modules.getEntry(url) orelse {
+        return error.UnknownModule;
+    };
+    const sync = entry.value_ptr.*;
+
+    // We can have multiple scripts waiting for the same module in concurrency.
+    // We use the waiters to ensures only the last waiter deinit the resources.
+    sync.waiters += 1;
+    defer sync.waiters -= 1;
+
     var client = self.client;
-    try client.blockingRequest(.{
+    while (true) {
+        switch (sync.state) {
+            .loading => {},
+            .done => {
+                if (sync.waiters == 1) {
+                    // Our caller has its own higher level cache (caching the
+                    // actual compiled module). There's no reason for us to keep
+                    // this if we are the last waiter.
+                    defer self.sync_module_pool.destroy(sync);
+                    defer self.sync_modules.removeByPtr(entry.key_ptr);
+                    return .{
+                        .shared = false,
+                        .buffer = sync.buffer,
+                        .buffer_pool = &self.buffer_pool,
+                    };
+                }
+
+                return .{
+                    .shared = true,
+                    .buffer = sync.buffer,
+                    .buffer_pool = &self.buffer_pool,
+                };
+            },
+            .err => |err| return err,
+        }
+        // rely on http's timeout settings to avoid an endless/long loop.
+        _ = try client.tick(200);
+    }
+}
+
+pub fn getAsyncModule(self: *ScriptManager, url: [:0]const u8, cb: AsyncModule.Callback, cb_data: *anyopaque, referrer: []const u8) !void {
+    const async = try self.async_module_pool.create();
+    errdefer self.async_module_pool.destroy(async);
+
+    async.* = .{
+        .cb = cb,
+        .manager = self,
+        .cb_data = cb_data,
+    };
+
+    var headers = try self.client.newHeaders();
+    try self.page.requestCookie(.{}).headersForRequest(self.page.arena, url, &headers);
+
+    log.debug(.http, "script queue", .{
+        .url = url,
+        .ctx = "dynamic module",
+        .referrer = referrer,
+        .stack = self.page.js.stackTrace() catch "???",
+    });
+
+    try self.client.request(.{
         .url = url,
         .method = .GET,
         .headers = headers,
         .cookie_jar = self.page.cookie_jar,
-        .ctx = &blocking,
+        .ctx = async,
         .resource_type = .script,
-        .start_callback = if (log.enabled(.http, .debug)) Blocking.startCallback else null,
-        .header_callback = Blocking.headerCallback,
-        .data_callback = Blocking.dataCallback,
-        .done_callback = Blocking.doneCallback,
-        .error_callback = Blocking.errorCallback,
+        .start_callback = if (log.enabled(.http, .debug)) AsyncModule.startCallback else null,
+        .header_callback = AsyncModule.headerCallback,
+        .data_callback = AsyncModule.dataCallback,
+        .done_callback = AsyncModule.doneCallback,
+        .error_callback = AsyncModule.errorCallback,
     });
-
-    // rely on http's timeout settings to avoid an endless/long loop.
-    while (true) {
-        _ = try client.tick(200);
-        switch (blocking.state) {
-            .running => {},
-            .done => |result| return result,
-            .err => |err| return err,
-        }
-    }
 }
-
 pub fn staticScriptsDone(self: *ScriptManager) void {
     std.debug.assert(self.static_scripts_done == false);
     self.static_scripts_done = true;
+    self.evaluate();
 }
 
 // try to evaluate completed scripts (in order). This is called whenever a script
@@ -318,24 +413,10 @@ fn evaluate(self: *ScriptManager) void {
         return;
     }
 
-    if (self.is_blocking) {
-        // Cannot evaluate scripts while a blocking-load is in progress. Not
-        // only could that result in incorrect evaluation order, it could
-        // trigger another blocking request, while we're doing a blocking request.
-        return;
-    }
-
     const page = self.page;
     self.is_evaluating = true;
     defer self.is_evaluating = false;
 
-    // every script in asyncs_ready is ready to be evaluated.
-    while (self.asyncs_ready.first) |n| {
-        var pending_script: *PendingScript = @fieldParentPtr("node", n);
-        defer pending_script.deinit();
-        pending_script.script.eval(page);
-    }
-
     while (self.scripts.first) |n| {
         var pending_script: *PendingScript = @fieldParentPtr("node", n);
         if (pending_script.complete == false) {
@@ -385,6 +466,12 @@ pub fn isDone(self: *const ScriptManager) bool {
         self.deferreds.first == null; // and there are no more <script defer src=> to wait for
 }
 
+fn asyncScriptIsDone(self: *ScriptManager) void {
+    if (self.isDone()) {
+        self.page.documentIsComplete();
+    }
+}
+
 fn startCallback(transfer: *Http.Transfer) !void {
     const script: *PendingScript = @ptrCast(@alignCast(transfer.ctx));
     script.startCallback(transfer) catch |err| {
@@ -416,6 +503,38 @@ fn errorCallback(ctx: *anyopaque, err: anyerror) void {
     script.errorCallback(err);
 }
 
+fn parseImportmap(self: *ScriptManager, script: *const Script) !void {
+    const content = script.source.content();
+
+    const Imports = struct {
+        imports: std.json.ArrayHashMap([]const u8),
+    };
+
+    const imports = try std.json.parseFromSliceLeaky(
+        Imports,
+        self.page.arena,
+        content,
+        .{ .allocate = .alloc_always },
+    );
+
+    var iter = imports.imports.map.iterator();
+    while (iter.next()) |entry| {
+        // > Relative URLs are resolved to absolute URL addresses using the
+        // > base URL of the document containing the import map.
+        // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules#importing_modules_using_import_maps
+        const resolved_url = try URL.stitch(
+            self.page.arena,
+            entry.value_ptr.*,
+            self.page.url.raw,
+            .{ .alloc = .if_needed, .null_terminated = true },
+        );
+
+        try self.importmap.put(self.page.arena, entry.key_ptr.*, resolved_url);
+    }
+
+    return;
+}
+
 // A script which is pending execution.
 // It could be pending because:
 //   (a) we're still downloading its content or
@@ -493,11 +612,15 @@ pub const PendingScript = struct {
 
         const manager = self.manager;
         self.complete = true;
-        if (self.script.is_async) {
-            manager.asyncs.remove(&self.node);
-            manager.asyncs_ready.append(&self.node);
+        if (!self.script.is_async) {
+            manager.evaluate();
+            return;
         }
-        manager.evaluate();
+        // async script can be evaluated immediately
+        self.script.eval(manager.page);
+        self.deinit();
+        // asyncScriptIsDone must be run after the pending script is deinit.
+        manager.asyncScriptIsDone();
     }
 
     fn errorCallback(self: *PendingScript, err: anyerror) void {
@@ -521,7 +644,7 @@ pub const PendingScript = struct {
 
         const script = &self.script;
         if (script.is_async) {
-            return if (self.complete) &self.manager.asyncs_ready else &self.manager.asyncs;
+            return &self.manager.asyncs;
         }
 
         if (script.is_defer) {
@@ -543,11 +666,12 @@ const Script = struct {
     const Kind = enum {
         module,
         javascript,
+        importmap,
     };
 
     const Callback = union(enum) {
         string: []const u8,
-        function: Env.Function,
+        function: js.Function,
     };
 
     const Source = union(enum) {
@@ -583,8 +707,25 @@ const Script = struct {
             .cacheable = cacheable,
         });
 
-        const js_context = page.main_context;
-        var try_catch: Env.TryCatch = undefined;
+        // Handle importmap special case here: the content is a JSON containing
+        // imports.
+        if (self.kind == .importmap) {
+            page.script_manager.parseImportmap(self) catch |err| {
+                log.err(.browser, "parse importmap script", .{
+                    .err = err,
+                    .src = url,
+                    .kind = self.kind,
+                    .cacheable = cacheable,
+                });
+                self.executeCallback("onerror", page);
+                return;
+            };
+            self.executeCallback("onload", page);
+            return;
+        }
+
+        const js_context = page.js;
+        var try_catch: js.TryCatch = undefined;
         try_catch.init(js_context);
         defer try_catch.deinit();
 
@@ -594,8 +735,9 @@ const Script = struct {
                 .javascript => _ = js_context.eval(content, url) catch break :blk false,
                 .module => {
                     // We don't care about waiting for the evaluation here.
-                    _ = js_context.module(content, url, cacheable) catch break :blk false;
+                    js_context.module(false, content, url, cacheable) catch break :blk false;
                 },
+                .importmap => unreachable, // handled before the try/catch.
             }
             break :blk true;
         };
@@ -626,11 +768,11 @@ const Script = struct {
 
         switch (callback) {
             .string => |str| {
-                var try_catch: Env.TryCatch = undefined;
-                try_catch.init(page.main_context);
+                var try_catch: js.TryCatch = undefined;
+                try_catch.init(page.js);
                 defer try_catch.deinit();
 
-                _ = page.main_context.exec(str, typ) catch |err| {
+                _ = page.js.exec(str, typ) catch |err| {
                     const msg = try_catch.err(page.arena) catch @errorName(err) orelse "unknown";
                     log.warn(.user_script, "script callback", .{
                         .url = self.url,
@@ -648,7 +790,7 @@ const Script = struct {
                 };
                 defer parser.eventDestroy(loadevt);
 
-                var result: Env.Function.Result = undefined;
+                var result: js.Function.Result = undefined;
                 const iface = Event.toInterface(loadevt);
                 f.tryCall(void, .{iface}, &result) catch {
                     log.warn(.user_script, "script callback", .{
@@ -751,16 +893,17 @@ const BufferPool = struct {
     }
 };
 
-const Blocking = struct {
-    allocator: Allocator,
-    buffer_pool: *BufferPool,
-    state: State = .{ .running = {} },
+const SyncModule = struct {
+    manager: *ScriptManager,
     buffer: std.ArrayListUnmanaged(u8) = .{},
+    state: State = .loading,
+    // number of waiters for the module.
+    waiters: u8 = 0,
 
     const State = union(enum) {
-        running: void,
+        done,
+        loading,
         err: anyerror,
-        done: BlockingResult,
     };
 
     fn startCallback(transfer: *Http.Transfer) !void {
@@ -776,12 +919,13 @@ const Blocking = struct {
             .content_type = header.contentType(),
         });
 
+        var self: *SyncModule = @ptrCast(@alignCast(transfer.ctx));
         if (header.status != 200) {
+            self.finished(.{ .err = error.InvalidStatusCode });
             return error.InvalidStatusCode;
         }
 
-        var self: *Blocking = @ptrCast(@alignCast(transfer.ctx));
-        self.buffer = self.buffer_pool.get();
+        self.buffer = self.manager.buffer_pool.get();
     }
 
     fn dataCallback(transfer: *Http.Transfer, data: []const u8) !void {
@@ -791,8 +935,8 @@ const Blocking = struct {
         //     .blocking = true,
         // });
 
-        var self: *Blocking = @ptrCast(@alignCast(transfer.ctx));
-        self.buffer.appendSlice(self.allocator, data) catch |err| {
+        var self: *SyncModule = @ptrCast(@alignCast(transfer.ctx));
+        self.buffer.appendSlice(self.manager.allocator, data) catch |err| {
             log.err(.http, "SM.dataCallback", .{
                 .err = err,
                 .len = data.len,
@@ -804,29 +948,107 @@ const Blocking = struct {
     }
 
     fn doneCallback(ctx: *anyopaque) !void {
-        var self: *Blocking = @ptrCast(@alignCast(ctx));
-        self.state = .{ .done = .{
-            .buffer = self.buffer,
-            .buffer_pool = self.buffer_pool,
-        } };
+        var self: *SyncModule = @ptrCast(@alignCast(ctx));
+        self.finished(.done);
     }
 
     fn errorCallback(ctx: *anyopaque, err: anyerror) void {
-        var self: *Blocking = @ptrCast(@alignCast(ctx));
-        self.state = .{ .err = err };
-        self.buffer_pool.release(self.buffer);
+        var self: *SyncModule = @ptrCast(@alignCast(ctx));
+        self.finished(.{ .err = err });
+    }
+
+    fn finished(self: *SyncModule, state: State) void {
+        self.state = state;
     }
 };
 
-pub const BlockingResult = struct {
+pub const AsyncModule = struct {
+    cb: Callback,
+    cb_data: *anyopaque,
+    manager: *ScriptManager,
+    buffer: std.ArrayListUnmanaged(u8) = .{},
+
+    pub const Callback = *const fn (ptr: *anyopaque, result: anyerror!GetResult) void;
+
+    fn startCallback(transfer: *Http.Transfer) !void {
+        log.debug(.http, "script fetch start", .{ .req = transfer, .async = true });
+    }
+
+    fn headerCallback(transfer: *Http.Transfer) !void {
+        const header = &transfer.response_header.?;
+        log.debug(.http, "script header", .{
+            .req = transfer,
+            .async = true,
+            .status = header.status,
+            .content_type = header.contentType(),
+        });
+
+        if (header.status != 200) {
+            return error.InvalidStatusCode;
+        }
+
+        var self: *AsyncModule = @ptrCast(@alignCast(transfer.ctx));
+        self.buffer = self.manager.buffer_pool.get();
+    }
+
+    fn dataCallback(transfer: *Http.Transfer, data: []const u8) !void {
+        // too verbose
+        // log.debug(.http, "script data chunk", .{
+        //     .req = transfer,
+        //     .blocking = true,
+        // });
+
+        var self: *AsyncModule = @ptrCast(@alignCast(transfer.ctx));
+        self.buffer.appendSlice(self.manager.allocator, data) catch |err| {
+            log.err(.http, "SM.dataCallback", .{
+                .err = err,
+                .len = data.len,
+                .ascyn = true,
+                .transfer = transfer,
+            });
+            return err;
+        };
+    }
+
+    fn doneCallback(ctx: *anyopaque) !void {
+        var self: *AsyncModule = @ptrCast(@alignCast(ctx));
+        defer self.manager.async_module_pool.destroy(self);
+        self.cb(self.cb_data, .{
+            .shared = false,
+            .buffer = self.buffer,
+            .buffer_pool = &self.manager.buffer_pool,
+        });
+    }
+
+    fn errorCallback(ctx: *anyopaque, err: anyerror) void {
+        var self: *AsyncModule = @ptrCast(@alignCast(ctx));
+
+        if (err != error.Abort) {
+            self.cb(self.cb_data, err);
+        }
+
+        if (self.buffer.items.len > 0) {
+            self.manager.buffer_pool.release(self.buffer);
+        }
+
+        self.manager.async_module_pool.destroy(self);
+    }
+};
+
+pub const GetResult = struct {
     buffer: std.ArrayListUnmanaged(u8),
     buffer_pool: *BufferPool,
+    shared: bool,
 
-    pub fn deinit(self: *BlockingResult) void {
+    pub fn deinit(self: *GetResult) void {
+        // if the result is shared, don't deinit.
+        if (self.shared) {
+            return;
+        }
         self.buffer_pool.release(self.buffer);
     }
 
-    pub fn src(self: *const BlockingResult) []const u8 {
+    pub fn src(self: *const GetResult) []const u8 {
         return self.buffer.items;
     }
 };

src/browser/SlotChangeMonitor.zig

@@ -0,0 +1,189 @@
+const std = @import("std");
+
+const log = @import("../log.zig");
+const parser = @import("netsurf.zig");
+const collection = @import("dom/html_collection.zig");
+
+const Page = @import("page.zig").Page;
+
+const SlotChangeMonitor = @This();
+
+page: *Page,
+event_node: parser.EventNode,
+slots_changed: std.ArrayList(*parser.Slot),
+
+// Monitors the document in order to trigger slotchange events.
+pub fn init(page: *Page) !*SlotChangeMonitor {
+    // on the heap, we need a stable address for event_node
+    const self = try page.arena.create(SlotChangeMonitor);
+    self.* = .{
+        .page = page,
+        .slots_changed = .empty,
+        .event_node = .{ .func = mutationCallback },
+    };
+    const root = parser.documentToNode(parser.documentHTMLToDocument(page.window.document));
+
+    _ = try parser.eventTargetAddEventListener(
+        parser.toEventTarget(parser.Node, root),
+        "DOMNodeInserted",
+        &self.event_node,
+        false,
+    );
+
+    _ = try parser.eventTargetAddEventListener(
+        parser.toEventTarget(parser.Node, root),
+        "DOMNodeRemoved",
+        &self.event_node,
+        false,
+    );
+
+    _ = try parser.eventTargetAddEventListener(
+        parser.toEventTarget(parser.Node, root),
+        "DOMAttrModified",
+        &self.event_node,
+        false,
+    );
+
+    return self;
+}
+
+// Given a element, finds its slot, if any.
+pub fn findSlot(element: *parser.Element, page: *const Page) !?*parser.Slot {
+    const target_name = (try parser.elementGetAttribute(element, "slot")) orelse return null;
+    return findNamedSlot(element, target_name, page);
+}
+
+// Given an element and a name, find the slo, if any. This is only useful for
+// MutationEvents where findSlot is unreliable because parser.elementGetAttribute(element, "slot")
+// could return the new or old value.
+fn findNamedSlot(element: *parser.Element, target_name: []const u8, page: *const Page) !?*parser.Slot {
+    // I believe elements need to be added as direct descendents of the host,
+    // so we don't need to go find the host, we just grab the parent.
+    const host = parser.nodeParentNode(@ptrCast(element)) orelse return null;
+    const state = page.getNodeState(host) orelse return null;
+    const shadow_root = state.shadow_root orelse return null;
+
+    // if we're here, we found a host, now find the slot
+    var nodes = collection.HTMLCollectionByTagName(
+        @ptrCast(@alignCast(shadow_root.proto)),
+        "slot",
+        .{ .include_root = false },
+    );
+    for (0..1000) |i| {
+        const n = (try nodes.item(@intCast(i))) orelse return null;
+        const slot_name = (try parser.elementGetAttribute(@ptrCast(n), "name")) orelse "";
+        if (std.mem.eql(u8, target_name, slot_name)) {
+            return @ptrCast(n);
+        }
+    }
+    return null;
+}
+
+// Event callback from the mutation event, signaling either the addition of
+// a node, removal of a node, or a change in attribute
+fn mutationCallback(en: *parser.EventNode, event: *parser.Event) void {
+    const mutation_event = parser.eventToMutationEvent(event);
+    const self: *SlotChangeMonitor = @fieldParentPtr("event_node", en);
+    self._mutationCallback(mutation_event) catch |err| {
+        log.err(.web_api, "slot change callback", .{ .err = err });
+    };
+}
+
+fn _mutationCallback(self: *SlotChangeMonitor, event: *parser.MutationEvent) !void {
+    const event_type = parser.eventType(@ptrCast(event));
+    if (std.mem.eql(u8, event_type, "DOMNodeInserted")) {
+        const event_target = parser.eventTarget(@ptrCast(event)) orelse return;
+        return self.nodeAddedOrRemoved(@ptrCast(event_target));
+    }
+
+    if (std.mem.eql(u8, event_type, "DOMNodeRemoved")) {
+        const event_target = parser.eventTarget(@ptrCast(event)) orelse return;
+        return self.nodeAddedOrRemoved(@ptrCast(event_target));
+    }
+
+    if (std.mem.eql(u8, event_type, "DOMAttrModified")) {
+        const attribute_name = try parser.mutationEventAttributeName(event);
+        if (std.mem.eql(u8, attribute_name, "slot") == false) {
+            return;
+        }
+
+        const new_value = parser.mutationEventNewValue(event);
+        const prev_value = parser.mutationEventPrevValue(event);
+        const event_target = parser.eventTarget(@ptrCast(event)) orelse return;
+        return self.nodeAttributeChanged(@ptrCast(event_target), new_value, prev_value);
+    }
+}
+
+// A node was removed or added. If it's an element, and if it has a slot attribute
+// then we'll dispatch a slotchange event.
+fn nodeAddedOrRemoved(self: *SlotChangeMonitor, node: *parser.Node) !void {
+    if (parser.nodeType(node) != .element) {
+        return;
+    }
+    const el: *parser.Element = @ptrCast(node);
+    if (try findSlot(el, self.page)) |slot| {
+        return self.scheduleSlotChange(slot);
+    }
+}
+
+// An attribute was modified. If the attribute is "slot", then we'll trigger 1
+// slotchange for the old slot (if there was one) and 1 slotchange for the new
+// one (if there is one)
+fn nodeAttributeChanged(self: *SlotChangeMonitor, node: *parser.Node, new_value: ?[]const u8, prev_value: ?[]const u8) !void {
+    if (parser.nodeType(node) != .element) {
+        return;
+    }
+
+    const el: *parser.Element = @ptrCast(node);
+    if (try findNamedSlot(el, prev_value orelse "", self.page)) |slot| {
+        try self.scheduleSlotChange(slot);
+    }
+
+    if (try findNamedSlot(el, new_value orelse "", self.page)) |slot| {
+        try self.scheduleSlotChange(slot);
+    }
+}
+
+// OK. Our MutationEvent is not a MutationObserver - it's an older, deprecated
+// API. It gets dispatched in the middle of the change. While I'm sure it has
+// some rules, from our point of view, it fires too early. DOMAttrModified fires
+// before the attribute is actually updated and DOMNodeRemoved before the node
+// is actually removed. This is a problem if the callback will call
+// `slot.assignedNodes`, since that won't return the new state.
+// So, we use the page schedule to schedule the dispatching of the slotchange
+// event.
+fn scheduleSlotChange(self: *SlotChangeMonitor, slot: *parser.Slot) !void {
+    for (self.slots_changed.items) |changed| {
+        if (slot == changed) {
+            return;
+        }
+    }
+
+    try self.slots_changed.append(self.page.arena, slot);
+    if (self.slots_changed.items.len == 1) {
+        // first item added, schedule the callback
+        try self.page.scheduler.add(self, scheduleCallback, 0, .{ .name = "slot change" });
+    }
+}
+
+// Callback from the schedule. Time to dispatch the slotchange event
+fn scheduleCallback(ctx: *anyopaque) ?u32 {
+    var self: *SlotChangeMonitor = @ptrCast(@alignCast(ctx));
+    self._scheduleCallback() catch |err| {
+        log.err(.app, "slot change schedule", .{ .err = err });
+    };
+    return null;
+}
+
+fn _scheduleCallback(self: *SlotChangeMonitor) !void {
+    for (self.slots_changed.items) |slot| {
+        const event = try parser.eventCreate();
+        defer parser.eventDestroy(event);
+        try parser.eventInit(event, "slotchange", .{});
+        _ = try parser.eventTargetDispatchEvent(
+            parser.toEventTarget(parser.Element, @ptrCast(@alignCast(slot))),
+            event,
+        );
+    }
+    self.slots_changed.clearRetainingCapacity();
+}

src/browser/State.zig

@@ -26,17 +26,16 @@
 // this quickly proved necessary, since different fields are needed on the same
 // data at different levels of the prototype chain. This isn't memory efficient.
 
-const Env = @import("env.zig").Env;
+const js = @import("js/js.zig");
 const parser = @import("netsurf.zig");
 const DataSet = @import("html/DataSet.zig");
 const ShadowRoot = @import("dom/shadow_root.zig").ShadowRoot;
 const StyleSheet = @import("cssom/StyleSheet.zig");
-const CSSStyleSheet = @import("cssom/CSSStyleSheet.zig");
 const CSSStyleDeclaration = @import("cssom/CSSStyleDeclaration.zig");
 
 // for HTMLScript (but probably needs to be added to more)
-onload: ?Env.Function = null,
-onerror: ?Env.Function = null,
+onload: ?js.Function = null,
+onerror: ?js.Function = null,
 
 // for HTMLElement
 style: CSSStyleDeclaration = .empty,
@@ -54,7 +53,7 @@ style_sheet: ?*StyleSheet = null,
 
 // for dom/document
 active_element: ?*parser.Element = null,
-adopted_style_sheets: ?Env.JsObject = null,
+adopted_style_sheets: ?js.Object = null,
 
 // for HTMLSelectElement
 // By default, if no option is explicitly selected, the first option should

src/browser/browser.zig

@@ -21,8 +21,8 @@ const std = @import("std");
 const Allocator = std.mem.Allocator;
 const ArenaAllocator = std.heap.ArenaAllocator;
 
+const js = @import("js/js.zig");
 const State = @import("State.zig");
-const Env = @import("env.zig").Env;
 const App = @import("../app.zig").App;
 const Session = @import("session.zig").Session;
 const Notification = @import("../notification.zig").Notification;
@@ -34,11 +34,12 @@ const HttpClient = @import("../http/Client.zig");
 // You can create multiple browser instances.
 // A browser contains only one session.
 pub const Browser = struct {
-    env: *Env,
+    env: *js.Env,
     app: *App,
     session: ?Session,
     allocator: Allocator,
     http_client: *HttpClient,
+    call_arena: ArenaAllocator,
     page_arena: ArenaAllocator,
     session_arena: ArenaAllocator,
     transfer_arena: ArenaAllocator,
@@ -48,7 +49,7 @@ pub const Browser = struct {
     pub fn init(app: *App) !Browser {
         const allocator = app.allocator;
 
-        const env = try Env.init(allocator, &app.platform, .{});
+        const env = try js.Env.init(allocator, &app.platform, .{});
         errdefer env.deinit();
 
         const notification = try Notification.init(allocator, app.notification);
@@ -63,6 +64,7 @@ pub const Browser = struct {
             .allocator = allocator,
             .notification = notification,
             .http_client = app.http.client,
+            .call_arena = ArenaAllocator.init(allocator),
             .page_arena = ArenaAllocator.init(allocator),
             .session_arena = ArenaAllocator.init(allocator),
             .transfer_arena = ArenaAllocator.init(allocator),
@@ -73,6 +75,7 @@ pub const Browser = struct {
     pub fn deinit(self: *Browser) void {
         self.closeSession();
         self.env.deinit();
+        self.call_arena.deinit();
         self.page_arena.deinit();
         self.session_arena.deinit();
         self.transfer_arena.deinit();

src/browser/console/console.zig

@@ -20,48 +20,47 @@ const std = @import("std");
 const builtin = @import("builtin");
 const log = @import("../../log.zig");
 
-const Allocator = std.mem.Allocator;
+const js = @import("../js/js.zig");
 const Page = @import("../page.zig").Page;
-const JsObject = @import("../env.zig").Env.JsObject;
 
 pub const Console = struct {
     // TODO: configurable writer
     timers: std.StringHashMapUnmanaged(u32) = .{},
     counts: std.StringHashMapUnmanaged(u32) = .{},
 
-    pub fn _lp(values: []JsObject, page: *Page) !void {
+    pub fn _lp(values: []js.Object, page: *Page) !void {
         if (values.len == 0) {
             return;
         }
         log.fatal(.console, "lightpanda", .{ .args = try serializeValues(values, page) });
     }
 
-    pub fn _log(values: []JsObject, page: *Page) !void {
+    pub fn _log(values: []js.Object, page: *Page) !void {
         if (values.len == 0) {
             return;
         }
         log.info(.console, "info", .{ .args = try serializeValues(values, page) });
     }
 
-    pub fn _info(values: []JsObject, page: *Page) !void {
+    pub fn _info(values: []js.Object, page: *Page) !void {
         return _log(values, page);
     }
 
-    pub fn _debug(values: []JsObject, page: *Page) !void {
+    pub fn _debug(values: []js.Object, page: *Page) !void {
         if (values.len == 0) {
             return;
         }
         log.debug(.console, "debug", .{ .args = try serializeValues(values, page) });
     }
 
-    pub fn _warn(values: []JsObject, page: *Page) !void {
+    pub fn _warn(values: []js.Object, page: *Page) !void {
         if (values.len == 0) {
             return;
         }
         log.warn(.console, "warn", .{ .args = try serializeValues(values, page) });
     }
 
-    pub fn _error(values: []JsObject, page: *Page) !void {
+    pub fn _error(values: []js.Object, page: *Page) !void {
         if (values.len == 0) {
             return;
         }
@@ -72,6 +71,16 @@ pub const Console = struct {
         });
     }
 
+    pub fn _trace(values: []js.Object, page: *Page) !void {
+        if (values.len == 0) {
+            return;
+        }
+        log.debug(.console, "debug", .{
+            .stack = page.js.stackTrace() catch "???",
+            .args = try serializeValues(values, page),
+        });
+    }
+
     pub fn _clear() void {}
 
     pub fn _count(self: *Console, label_: ?[]const u8, page: *Page) !void {
@@ -133,7 +142,7 @@ pub const Console = struct {
         log.warn(.console, "timer stop", .{ .label = label, .elapsed = elapsed - kv.value });
     }
 
-    pub fn _assert(assertion: JsObject, values: []JsObject, page: *Page) !void {
+    pub fn _assert(assertion: js.Object, values: []js.Object, page: *Page) !void {
         if (assertion.isTruthy()) {
             return;
         }
@@ -144,7 +153,7 @@ pub const Console = struct {
         log.info(.console, "assertion failed", .{ .values = serialized_values });
     }
 
-    fn serializeValues(values: []JsObject, page: *Page) ![]const u8 {
+    fn serializeValues(values: []js.Object, page: *Page) ![]const u8 {
         if (values.len == 0) {
             return "";
         }

src/browser/crypto/crypto.zig

@@ -17,14 +17,14 @@
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 const std = @import("std");
-const Env = @import("../env.zig").Env;
+const js = @import("../js/js.zig");
 const uuidv4 = @import("../../id.zig").uuidv4;
 
 // https://w3c.github.io/webcrypto/#crypto-interface
 pub const Crypto = struct {
     _not_empty: bool = true,
 
-    pub fn _getRandomValues(_: *const Crypto, js_obj: Env.JsObject) !Env.JsObject {
+    pub fn _getRandomValues(_: *const Crypto, js_obj: js.Object) !js.Object {
         var into = try js_obj.toZig(Crypto, "getRandomValues", RandomValues);
         const buf = into.asBuffer();
         if (buf.len > 65_536) {

src/browser/css/css.zig

@@ -46,17 +46,15 @@ pub fn parse(alloc: std.mem.Allocator, s: []const u8, opts: parser.ParseOptions)
 // matchFirst call m.match with the first node that matches the selector s, from the
 // descendants of n and returns true. If none matches, it returns false.
 pub fn matchFirst(s: *const Selector, node: anytype, m: anytype) !bool {
-    var c = try node.firstChild();
-    while (true) {
-        if (c == null) break;
-
-        if (try s.match(c.?)) {
-            try m.match(c.?);
+    var child = node.firstChild();
+    while (child) |c| {
+        if (try s.match(c)) {
+            try m.match(c);
             return true;
         }
 
-        if (try matchFirst(s, c.?, m)) return true;
-        c = try c.?.nextSibling();
+        if (try matchFirst(s, c, m)) return true;
+        child = c.nextSibling();
     }
     return false;
 }
@@ -64,13 +62,11 @@ pub fn matchFirst(s: *const Selector, node: anytype, m: anytype) !bool {
 // matchAll call m.match with the all the nodes that matches the selector s, from the
 // descendants of n.
 pub fn matchAll(s: *const Selector, node: anytype, m: anytype) !void {
-    var c = try node.firstChild();
-    while (true) {
-        if (c == null) break;
-
-        if (try s.match(c.?)) try m.match(c.?);
-        try matchAll(s, c.?, m);
-        c = try c.?.nextSibling();
+    var child = node.firstChild();
+    while (child) |c| {
+        if (try s.match(c)) try m.match(c);
+        try matchAll(s, c, m);
+        child = c.nextSibling();
     }
 }
 

src/browser/css/libdom.zig

@@ -26,71 +26,67 @@ const Allocator = std.mem.Allocator;
 pub const Node = struct {
     node: *parser.Node,
 
-    pub fn firstChild(n: Node) !?Node {
-        const c = try parser.nodeFirstChild(n.node);
+    pub fn firstChild(n: Node) ?Node {
+        const c = parser.nodeFirstChild(n.node);
         if (c) |cc| return .{ .node = cc };
 
         return null;
     }
 
-    pub fn lastChild(n: Node) !?Node {
-        const c = try parser.nodeLastChild(n.node);
+    pub fn lastChild(n: Node) ?Node {
+        const c = parser.nodeLastChild(n.node);
         if (c) |cc| return .{ .node = cc };
 
         return null;
     }
 
-    pub fn nextSibling(n: Node) !?Node {
-        const c = try parser.nodeNextSibling(n.node);
+    pub fn nextSibling(n: Node) ?Node {
+        const c = parser.nodeNextSibling(n.node);
         if (c) |cc| return .{ .node = cc };
 
         return null;
     }
 
-    pub fn prevSibling(n: Node) !?Node {
-        const c = try parser.nodePreviousSibling(n.node);
+    pub fn prevSibling(n: Node) ?Node {
+        const c = parser.nodePreviousSibling(n.node);
         if (c) |cc| return .{ .node = cc };
 
         return null;
     }
 
-    pub fn parent(n: Node) !?Node {
-        const c = try parser.nodeParentNode(n.node);
+    pub fn parent(n: Node) ?Node {
+        const c = parser.nodeParentNode(n.node);
         if (c) |cc| return .{ .node = cc };
 
         return null;
     }
 
     pub fn isElement(n: Node) bool {
-        const t = parser.nodeType(n.node) catch return false;
-        return t == .element;
+        return parser.nodeType(n.node) == .element;
     }
 
     pub fn isDocument(n: Node) bool {
-        const t = parser.nodeType(n.node) catch return false;
-        return t == .document;
+        return parser.nodeType(n.node) == .document;
     }
 
     pub fn isComment(n: Node) bool {
-        const t = parser.nodeType(n.node) catch return false;
-        return t == .comment;
+        return parser.nodeType(n.node) == .comment;
     }
 
     pub fn isText(n: Node) bool {
-        const t = parser.nodeType(n.node) catch return false;
-        return t == .text;
+        return parser.nodeType(n.node) == .text;
     }
 
-    pub fn text(n: Node) !?[]const u8 {
-        const data = try parser.nodeTextContent(n.node);
+    pub fn text(n: Node) ?[]const u8 {
+        const data = parser.nodeTextContent(n.node);
         if (data == null) return null;
         if (data.?.len == 0) return null;
 
         return std.mem.trim(u8, data.?, &std.ascii.whitespace);
     }
 
-    pub fn isEmptyText(n: Node) !bool {
-        const data = try parser.nodeTextContent(n.node);
+    pub fn isEmptyText(n: Node) bool {
+        const data = parser.nodeTextContent(n.node);
         if (data == null) return true;
         if (data.?.len == 0) return true;
 
@@ -98,7 +94,7 @@ pub const Node = struct {
     }
 
     pub fn tag(n: Node) ![]const u8 {
-        return try parser.nodeName(n.node);
+        return parser.nodeName(n.node);
     }
 
     pub fn attr(n: Node, key: []const u8) !?[]const u8 {
@@ -140,7 +136,7 @@ const MatcherTest = struct {
 test "Browser.CSS.Libdom: matchFirst" {
     const alloc = std.testing.allocator;
 
-    try parser.init();
+    parser.init();
     defer parser.deinit();
 
     var matcher = MatcherTest.init(alloc);
@@ -285,7 +281,7 @@ test "Browser.CSS.Libdom: matchFirst" {
 test "Browser.CSS.Libdom: matchAll" {
     const alloc = std.testing.allocator;
 
-    try parser.init();
+    parser.init();
     defer parser.deinit();
 
     var matcher = MatcherTest.init(alloc);

src/browser/css/parser.zig

@@ -821,7 +821,8 @@ pub const Parser = struct {
 // nameStart returns whether c can be the first character of an identifier
 // (not counting an initial hyphen, or an escape sequence).
 fn nameStart(c: u8) bool {
-    return 'a' <= c and c <= 'z' or 'A' <= c and c <= 'Z' or c == '_' or c > 127;
+    return 'a' <= c and c <= 'z' or 'A' <= c and c <= 'Z' or c == '_' or c > 127 or
+        '0' <= c and c <= '9';
 }
 
 // nameChar returns whether c can be a character within an identifier
@@ -890,7 +891,7 @@ test "parser.parseIdentifier" {
         err: bool = false,
     }{
         .{ .s = "x", .exp = "x" },
-        .{ .s = "96", .exp = "", .err = true },
+        .{ .s = "96", .exp = "96", .err = false },
         .{ .s = "-x", .exp = "-x" },
         .{ .s = "r\\e9 sumé", .exp = "résumé" },
         .{ .s = "r\\0000e9 sumé", .exp = "résumé" },
@@ -975,6 +976,7 @@ test "parser.parse" {
         .{ .s = ":root", .exp = .{ .pseudo_class = .root } },
         .{ .s = ".\\:bar", .exp = .{ .class = ":bar" } },
         .{ .s = ".foo\\:bar", .exp = .{ .class = "foo:bar" } },
+        .{ .s = "[class=75c0fa18a94b9e3a6b8e14d6cbe688a27f5da10a]", .exp = .{ .attribute = .{ .key = "class", .val = "75c0fa18a94b9e3a6b8e14d6cbe688a27f5da10a", .op = .eql } } },
     };
 
     for (testcases) |tc| {

src/browser/css/selector.zig

@@ -334,41 +334,39 @@ pub const Selector = union(enum) {
                         if (!try v.second.match(n)) return false;
 
                         // The first must match a ascendent.
-                        var p = try n.parent();
-                        while (p != null) {
-                            if (try v.first.match(p.?)) {
+                        var parent = n.parent();
+                        while (parent) |p| {
+                            if (try v.first.match(p)) {
                                 return true;
                             }
-                            p = try p.?.parent();
+                            parent = p.parent();
                         }
 
                         return false;
                     },
                     .child => {
-                        const p = try n.parent();
-                        if (p == null) return false;
-
-                        return try v.second.match(n) and try v.first.match(p.?);
+                        const p = n.parent() orelse return false;
+                        return try v.second.match(n) and try v.first.match(p);
                     },
                     .next_sibling => {
                         if (!try v.second.match(n)) return false;
-                        var c = try n.prevSibling();
-                        while (c != null) {
-                            if (c.?.isText() or c.?.isComment()) {
-                                c = try c.?.prevSibling();
+                        var child = n.prevSibling();
+                        while (child) |c| {
+                            if (c.isText() or c.isComment()) {
+                                child = c.prevSibling();
                                 continue;
                             }
-                            return try v.first.match(c.?);
+                            return try v.first.match(c);
                         }
                         return false;
                     },
                     .subsequent_sibling => {
                         if (!try v.second.match(n)) return false;
 
-                        var c = try n.prevSibling();
-                        while (c != null) {
-                            if (try v.first.match(c.?)) return true;
-                            c = try c.?.prevSibling();
+                        var child = n.prevSibling();
+                        while (child) |c| {
+                            if (try v.first.match(c)) return true;
+                            child = c.prevSibling();
                         }
                         return false;
                     },
@@ -438,10 +436,10 @@ pub const Selector = union(enum) {
                 // Only containsOwn is implemented.
                 if (v.own == false) return Error.UnsupportedContainsPseudoClass;
 
-                var c = try n.firstChild();
-                while (c != null) {
-                    if (c.?.isText()) {
-                        const text = try c.?.text();
+                var child = n.firstChild();
+                while (child) |c| {
+                    if (c.isText()) {
+                        const text = c.text();
                         if (text) |_text| {
                             if (contains(_text, v.val, false)) { // we are case sensitive. Is this correct behavior?
                                 return true;
@@ -449,7 +447,7 @@ pub const Selector = union(enum) {
                         }
                     }
 
-                    c = try c.?.nextSibling();
+                    child = c.nextSibling();
                 }
                 return false;
             },
@@ -477,16 +475,16 @@ pub const Selector = union(enum) {
                     .empty => {
                         if (!n.isElement()) return false;
 
-                        var c = try n.firstChild();
-                        while (c != null) {
-                            if (c.?.isElement()) return false;
+                        var child = n.firstChild();
+                        while (child) |c| {
+                            if (c.isElement()) return false;
 
-                            if (c.?.isText()) {
-                                if (try c.?.isEmptyText()) continue;
+                            if (c.isText()) {
+                                if (c.isEmptyText()) continue;
                                 return false;
                             }
 
-                            c = try c.?.nextSibling();
+                            child = c.nextSibling();
                         }
 
                         return true;
@@ -494,7 +492,7 @@ pub const Selector = union(enum) {
                     .root => {
                         if (!n.isElement()) return false;
 
-                        const p = try n.parent();
+                        const p = n.parent();
                         return (p != null and p.?.isDocument());
                     },
                     .link => {
@@ -564,7 +562,7 @@ pub const Selector = union(enum) {
 
                         const ntag = try n.tag();
 
-                        if (std.ascii.eqlIgnoreCase("intput", ntag)) {
+                        if (std.ascii.eqlIgnoreCase("input", ntag)) {
                             const ntype = try n.attr("type");
                             if (ntype == null) return false;
 
@@ -609,24 +607,23 @@ pub const Selector = union(enum) {
     }
 
     fn hasLegendInPreviousSiblings(n: anytype) anyerror!bool {
-        var c = try n.prevSibling();
-        while (c != null) {
-            const ctag = try c.?.tag();
+        var child = n.prevSibling();
+        while (child) |c| {
+            const ctag = try c.tag();
             if (std.ascii.eqlIgnoreCase("legend", ctag)) return true;
-            c = try c.?.prevSibling();
+            child = c.prevSibling();
         }
         return false;
     }
 
     fn inDisabledFieldset(n: anytype) anyerror!bool {
-        const p = try n.parent();
-        if (p == null) return false;
+        const p = n.parent() orelse return false;
 
         const ntag = try n.tag();
-        const ptag = try p.?.tag();
+        const ptag = try p.tag();
 
         if (std.ascii.eqlIgnoreCase("fieldset", ptag) and
-            try p.?.attr("disabled") != null and
+            try p.attr("disabled") != null and
             (!std.ascii.eqlIgnoreCase("legend", ntag) or try hasLegendInPreviousSiblings(n)))
         {
             return true;
@@ -642,7 +639,7 @@ pub const Selector = union(enum) {
         // ```
         // https://github.com/andybalholm/cascadia/blob/master/pseudo_classes.go#L434
 
-        return try inDisabledFieldset(p.?);
+        return try inDisabledFieldset(p);
     }
 
     fn langMatch(lang: []const u8, n: anytype) anyerror!bool {
@@ -656,10 +653,8 @@ pub const Selector = union(enum) {
         }
 
         // if the tag doesn't match, try the parent.
-        const p = try n.parent();
-        if (p == null) return false;
-
-        return langMatch(lang, p.?);
+        const p = n.parent() orelse return false;
+        return langMatch(lang, p);
     }
 
     // onlyChildMatch implements :only-child
@@ -667,25 +662,24 @@ pub const Selector = union(enum) {
     fn onlyChildMatch(of_type: bool, n: anytype) anyerror!bool {
         if (!n.isElement()) return false;
 
-        const p = try n.parent();
-        if (p == null) return false;
+        const p = n.parent() orelse return false;
 
         const ntag = try n.tag();
 
         var count: usize = 0;
-        var c = try p.?.firstChild();
+        var child = p.firstChild();
         // loop hover all n siblings.
-        while (c != null) {
+        while (child) |c| {
             // ignore non elements or others tags if of-type is true.
-            if (!c.?.isElement() or (of_type and !std.mem.eql(u8, ntag, try c.?.tag()))) {
-                c = try c.?.nextSibling();
+            if (!c.isElement() or (of_type and !std.mem.eql(u8, ntag, try c.tag()))) {
+                child = c.nextSibling();
                 continue;
             }
 
             count += 1;
             if (count > 1) return false;
 
-            c = try c.?.nextSibling();
+            child = c.nextSibling();
         }
 
         return count == 1;
@@ -696,27 +690,25 @@ pub const Selector = union(enum) {
     fn simpleNthLastChildMatch(b: isize, of_type: bool, n: anytype) anyerror!bool {
         if (!n.isElement()) return false;
 
-        const p = try n.parent();
-        if (p == null) return false;
-
+        const p = n.parent() orelse return false;
         const ntag = try n.tag();
 
         var count: isize = 0;
-        var c = try p.?.lastChild();
+        var child = p.lastChild();
         // loop hover all n siblings.
-        while (c != null) {
+        while (child) |c| {
             // ignore non elements or others tags if of-type is true.
-            if (!c.?.isElement() or (of_type and !std.mem.eql(u8, ntag, try c.?.tag()))) {
-                c = try c.?.prevSibling();
+            if (!c.isElement() or (of_type and !std.mem.eql(u8, ntag, try c.tag()))) {
+                child = c.prevSibling();
                 continue;
             }
 
             count += 1;
 
-            if (n.eql(c.?)) return count == b;
+            if (n.eql(c)) return count == b;
             if (count >= b) return false;
 
-            c = try c.?.prevSibling();
+            child = c.prevSibling();
         }
 
         return false;
@@ -727,27 +719,25 @@ pub const Selector = union(enum) {
     fn simpleNthChildMatch(b: isize, of_type: bool, n: anytype) anyerror!bool {
         if (!n.isElement()) return false;
 
-        const p = try n.parent();
-        if (p == null) return false;
-
+        const p = n.parent() orelse return false;
         const ntag = try n.tag();
 
         var count: isize = 0;
-        var c = try p.?.firstChild();
+        var child = p.firstChild();
         // loop hover all n siblings.
-        while (c != null) {
+        while (child) |c| {
             // ignore non elements or others tags if of-type is true.
-            if (!c.?.isElement() or (of_type and !std.mem.eql(u8, ntag, try c.?.tag()))) {
-                c = try c.?.nextSibling();
+            if (!c.isElement() or (of_type and !std.mem.eql(u8, ntag, try c.tag()))) {
+                child = c.nextSibling();
                 continue;
             }
 
             count += 1;
 
-            if (n.eql(c.?)) return count == b;
+            if (n.eql(c)) return count == b;
             if (count >= b) return false;
 
-            c = try c.?.nextSibling();
+            child = c.nextSibling();
         }
 
         return false;
@@ -759,29 +749,27 @@ pub const Selector = union(enum) {
     fn nthChildMatch(a: isize, b: isize, last: bool, of_type: bool, n: anytype) anyerror!bool {
         if (!n.isElement()) return false;
 
-        const p = try n.parent();
-        if (p == null) return false;
-
+        const p = n.parent() orelse return false;
         const ntag = try n.tag();
 
         var i: isize = -1;
         var count: isize = 0;
-        var c = try p.?.firstChild();
+        var child = p.firstChild();
         // loop hover all n siblings.
-        while (c != null) {
+        while (child) |c| {
             // ignore non elements or others tags if of-type is true.
-            if (!c.?.isElement() or (of_type and !std.mem.eql(u8, ntag, try c.?.tag()))) {
-                c = try c.?.nextSibling();
+            if (!c.isElement() or (of_type and !std.mem.eql(u8, ntag, try c.tag()))) {
+                child = c.nextSibling();
                 continue;
             }
             count += 1;
 
-            if (n.eql(c.?)) {
+            if (n.eql(c)) {
                 i = count;
                 if (!last) break;
             }
 
-            c = try c.?.nextSibling();
+            child = c.nextSibling();
         }
 
         if (i == -1) return false;
@@ -794,21 +782,21 @@ pub const Selector = union(enum) {
     }
 
     fn hasDescendantMatch(s: *const Selector, n: anytype) anyerror!bool {
-        var c = try n.firstChild();
-        while (c != null) {
-            if (try s.match(c.?)) return true;
-            if (c.?.isElement() and try hasDescendantMatch(s, c.?)) return true;
-            c = try c.?.nextSibling();
+        var child = n.firstChild();
+        while (child) |c| {
+            if (try s.match(c)) return true;
+            if (c.isElement() and try hasDescendantMatch(s, c)) return true;
+            child = c.nextSibling();
         }
 
         return false;
     }
 
     fn hasChildMatch(s: *const Selector, n: anytype) anyerror!bool {
-        var c = try n.firstChild();
-        while (c != null) {
-            if (try s.match(c.?)) return true;
-            c = try c.?.nextSibling();
+        var child = n.firstChild();
+        while (child) |c| {
+            if (try s.match(c)) return true;
+            child = c.nextSibling();
         }
 
         return false;
@@ -859,23 +847,23 @@ pub const NodeTest = struct {
     name: []const u8 = "",
     att: ?[]const u8 = null,
 
-    pub fn firstChild(n: *const NodeTest) !?*const NodeTest {
+    pub fn firstChild(n: *const NodeTest) ?*const NodeTest {
         return n.child;
     }
 
-    pub fn lastChild(n: *const NodeTest) !?*const NodeTest {
+    pub fn lastChild(n: *const NodeTest) ?*const NodeTest {
         return n.last;
     }
 
-    pub fn nextSibling(n: *const NodeTest) !?*const NodeTest {
+    pub fn nextSibling(n: *const NodeTest) ?*const NodeTest {
         return n.sibling;
     }
 
-    pub fn prevSibling(n: *const NodeTest) !?*const NodeTest {
+    pub fn prevSibling(n: *const NodeTest) ?*const NodeTest {
         return n.prev;
     }
 
-    pub fn parent(n: *const NodeTest) !?*const NodeTest {
+    pub fn parent(n: *const NodeTest) ?*const NodeTest {
         return n.par;
     }
 
@@ -891,7 +879,7 @@ pub const NodeTest = struct {
         return false;
     }
 
-    pub fn text(_: *const NodeTest) !?[]const u8 {
+    pub fn text(_: *const NodeTest) ?[]const u8 {
         return null;
     }
 
@@ -899,7 +887,7 @@ pub const NodeTest = struct {
         return false;
     }
 
-    pub fn isEmptyText(_: *const NodeTest) !bool {
+    pub fn isEmptyText(_: *const NodeTest) bool {
         return false;
     }
 
@@ -993,6 +981,11 @@ test "Browser.CSS.Selector: matchFirst" {
             .n = .{ .child = &.{ .name = "p", .sibling = &.{ .name = "p", .att = "bar" } } },
             .exp = 0,
         },
+        .{
+            .q = "[foo=1baz]",
+            .n = .{ .child = &.{ .name = "p", .sibling = &.{ .name = "p", .att = "bar" } } },
+            .exp = 0,
+        },
         .{
             .q = "[foo!=bar]",
             .n = .{ .child = &.{ .name = "p", .sibling = &.{ .name = "p", .att = "bar" } } },

src/browser/cssom/CSSRuleList.zig

@@ -19,7 +19,6 @@
 const std = @import("std");
 
 const CSSRule = @import("CSSRule.zig");
-const StyleSheet = @import("StyleSheet.zig").StyleSheet;
 
 const CSSImportRule = CSSRule.CSSImportRule;
 

src/browser/cssom/CSSStyleSheet.zig

@@ -18,7 +18,7 @@
 
 const std = @import("std");
 
-const Env = @import("../env.zig").Env;
+const js = @import("../js/js.zig");
 const Page = @import("../page.zig").Page;
 const StyleSheet = @import("StyleSheet.zig");
 const CSSRuleList = @import("CSSRuleList.zig");
@@ -73,15 +73,13 @@ pub fn _deleteRule(self: *CSSStyleSheet, index: usize) !void {
     _ = self.css_rules.list.orderedRemove(index);
 }
 
-pub fn _replace(self: *CSSStyleSheet, text: []const u8, page: *Page) !Env.Promise {
+pub fn _replace(self: *CSSStyleSheet, text: []const u8, page: *Page) !js.Promise {
     _ = self;
     _ = text;
     // TODO: clear self.css_rules
     // parse text and re-populate self.css_rules
 
-    const resolver = page.main_context.createPromiseResolver();
-    try resolver.resolve({});
-    return resolver.promise();
+    return page.js.resolvePromise({});
 }
 
 pub fn _replaceSync(self: *CSSStyleSheet, text: []const u8) !void {

src/browser/dom/Animation.zig

@@ -18,19 +18,17 @@
 
 const std = @import("std");
 
+const js = @import("../js/js.zig");
 const Page = @import("../page.zig").Page;
-const JsObject = @import("../env.zig").JsObject;
-const Promise = @import("../env.zig").Promise;
-const PromiseResolver = @import("../env.zig").PromiseResolver;
 
 const Animation = @This();
 
-effect: ?JsObject,
-timeline: ?JsObject,
-ready_resolver: ?PromiseResolver,
-finished_resolver: ?PromiseResolver,
+effect: ?js.Object,
+timeline: ?js.Object,
+ready_resolver: ?js.PromiseResolver,
+finished_resolver: ?js.PromiseResolver,
 
-pub fn constructor(effect: ?JsObject, timeline: ?JsObject) !Animation {
+pub fn constructor(effect: ?js.Object, timeline: ?js.Object) !Animation {
     return .{
         .effect = if (effect) |eo| try eo.persist() else null,
         .timeline = if (timeline) |to| try to.persist() else null,
@@ -49,37 +47,37 @@ pub fn get_pending(self: *const Animation) bool {
     return false;
 }
 
-pub fn get_finished(self: *Animation, page: *Page) !Promise {
+pub fn get_finished(self: *Animation, page: *Page) !js.Promise {
     if (self.finished_resolver == null) {
-        const resolver = page.main_context.createPromiseResolver();
+        const resolver = page.js.createPromiseResolver(.none);
         try resolver.resolve(self);
         self.finished_resolver = resolver;
     }
     return self.finished_resolver.?.promise();
 }
 
-pub fn get_ready(self: *Animation, page: *Page) !Promise {
+pub fn get_ready(self: *Animation, page: *Page) !js.Promise {
     // never resolved, because we're always "finished"
     if (self.ready_resolver == null) {
-        const resolver = page.main_context.createPromiseResolver();
+        const resolver = page.js.createPromiseResolver(.none);
         self.ready_resolver = resolver;
     }
     return self.ready_resolver.?.promise();
 }
 
-pub fn get_effect(self: *const Animation) ?JsObject {
+pub fn get_effect(self: *const Animation) ?js.Object {
     return self.effect;
 }
 
-pub fn set_effect(self: *Animation, effect: JsObject) !void {
+pub fn set_effect(self: *Animation, effect: js.Object) !void {
     self.effect = try effect.persist();
 }
 
-pub fn get_timeline(self: *const Animation) ?JsObject {
+pub fn get_timeline(self: *const Animation) ?js.Object {
     return self.timeline;
 }
 
-pub fn set_timeline(self: *Animation, timeline: JsObject) !void {
+pub fn set_timeline(self: *Animation, timeline: js.Object) !void {
     self.timeline = try timeline.persist();
 }
 

src/browser/dom/IntersectionObserver.zig

@@ -0,0 +1,329 @@
+// Copyright (C) 2023-2025  Lightpanda (Selecy SAS)
+//
+// Francis Bouvier <francis@lightpanda.io>
+// Pierre Tachoire <pierre@lightpanda.io>
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as
+// published by the Free Software Foundation, either version 3 of the
+// License, or (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+const std = @import("std");
+
+const js = @import("../js/js.zig");
+const log = @import("../../log.zig");
+const parser = @import("../netsurf.zig");
+const Page = @import("../page.zig").Page;
+const Node = @import("node.zig").Node;
+const Element = @import("element.zig").Element;
+
+pub const Interfaces = .{
+    IntersectionObserver,
+    Entry,
+};
+
+// This implementation attempts to be as less wrong as possible. Since we don't
+// render, or know how things are positioned, our best guess isn't very good.
+const IntersectionObserver = @This();
+page: *Page,
+root: *parser.Node,
+callback: js.Function,
+event_node: parser.EventNode,
+observed_entries: std.ArrayList(Entry),
+pending_elements: std.ArrayList(*parser.Element),
+ready_elements: std.ArrayList(*parser.Element),
+
+pub fn constructor(callback: js.Function, opts_: ?IntersectionObserverOptions, page: *Page) !*IntersectionObserver {
+    const opts = opts_ orelse IntersectionObserverOptions{};
+
+    const self = try page.arena.create(IntersectionObserver);
+    self.* = .{
+        .page = page,
+        .callback = callback,
+        .ready_elements = .{},
+        .observed_entries = .{},
+        .pending_elements = .{},
+        .event_node = .{ .func = mutationCallback },
+        .root = opts.root orelse parser.documentToNode(parser.documentHTMLToDocument(page.window.document)),
+    };
+
+    _ = try parser.eventTargetAddEventListener(
+        parser.toEventTarget(parser.Node, self.root),
+        "DOMNodeInserted",
+        &self.event_node,
+        false,
+    );
+
+    _ = try parser.eventTargetAddEventListener(
+        parser.toEventTarget(parser.Node, self.root),
+        "DOMNodeRemoved",
+        &self.event_node,
+        false,
+    );
+
+    return self;
+}
+
+pub fn _disconnect(self: *IntersectionObserver) !void {
+    // We don't free as it is on an arena
+    self.ready_elements = .{};
+    self.observed_entries = .{};
+    self.pending_elements = .{};
+}
+
+pub fn _observe(self: *IntersectionObserver, target_element: *parser.Element, page: *Page) !void {
+    for (self.observed_entries.items) |*observer| {
+        if (observer.target == target_element) {
+            return; // Already observed
+        }
+    }
+
+    if (self.isPending(target_element)) {
+        return; // Already pending
+    }
+
+    for (self.ready_elements.items) |element| {
+        if (element == target_element) {
+            return; // Already primed
+        }
+    }
+
+    // We can never fire callbacks synchronously. Code like React expects any
+    // callback to fire in the future (e.g. via microtasks).
+    try self.ready_elements.append(self.page.arena, target_element);
+    if (self.ready_elements.items.len == 1) {
+        // this is our first ready entry, schedule a callback
+        try page.scheduler.add(self, processReady, 0, .{
+            .name = "intersection ready",
+        });
+    }
+}
+
+pub fn _unobserve(self: *IntersectionObserver, target: *parser.Element) !void {
+    if (self.removeObserved(target)) {
+        return;
+    }
+
+    for (self.ready_elements.items, 0..) |el, index| {
+        if (el == target) {
+            _ = self.ready_elements.swapRemove(index);
+            return;
+        }
+    }
+
+    for (self.pending_elements.items, 0..) |el, index| {
+        if (el == target) {
+            _ = self.pending_elements.swapRemove(index);
+            return;
+        }
+    }
+}
+
+pub fn _takeRecords(self: *IntersectionObserver) []Entry {
+    return self.observed_entries.items;
+}
+
+fn processReady(ctx: *anyopaque) ?u32 {
+    const self: *IntersectionObserver = @ptrCast(@alignCast(ctx));
+    self._processReady() catch |err| {
+        log.err(.web_api, "intersection ready", .{ .err = err });
+    };
+    return null;
+}
+
+fn _processReady(self: *IntersectionObserver) !void {
+    defer self.ready_elements.clearRetainingCapacity();
+    for (self.ready_elements.items) |element| {
+        // IntersectionObserver probably doesn't work like what your intuition
+        // thinks. As long as a node has a parent, even if that parent isn't
+        // connected and even if the two nodes don't intersect, it'll fire the
+        // callback once.
+        if (try Node.get_parentNode(@ptrCast(element)) == null) {
+            if (!self.isPending(element)) {
+                try self.pending_elements.append(self.page.arena, element);
+            }
+            continue;
+        }
+        try self.forceObserve(element);
+    }
+}
+
+fn isPending(self: *IntersectionObserver, element: *parser.Element) bool {
+    for (self.pending_elements.items) |el| {
+        if (el == element) {
+            return true;
+        }
+    }
+    return false;
+}
+
+fn mutationCallback(en: *parser.EventNode, event: *parser.Event) void {
+    const mutation_event = parser.eventToMutationEvent(event);
+    const self: *IntersectionObserver = @fieldParentPtr("event_node", en);
+    self._mutationCallback(mutation_event) catch |err| {
+        log.err(.web_api, "mutation callback", .{ .err = err, .source = "intersection observer" });
+    };
+}
+
+fn _mutationCallback(self: *IntersectionObserver, event: *parser.MutationEvent) !void {
+    const event_type = parser.eventType(@ptrCast(event));
+
+    if (std.mem.eql(u8, event_type, "DOMNodeInserted")) {
+        const node = parser.mutationEventRelatedNode(event) catch return orelse return;
+        if (parser.nodeType(node) != .element) {
+            return;
+        }
+        const el: *parser.Element = @ptrCast(node);
+        if (self.removePending(el)) {
+            // It was pending (because it wasn't in the root), but now it is
+            // we should observe it.
+            try self.forceObserve(el);
+        }
+        return;
+    }
+
+    if (std.mem.eql(u8, event_type, "DOMNodeRemoved")) {
+        const node = parser.mutationEventRelatedNode(event) catch return orelse return;
+        if (parser.nodeType(node) != .element) {
+            return;
+        }
+
+        const el: *parser.Element = @ptrCast(node);
+        if (self.removeObserved(el)) {
+            // It _was_ observed, it no longer is in our root, but if it was
+            // to get re-added, it should be observed again (I think), so
+            // we add it to our pending list
+            try self.pending_elements.append(self.page.arena, el);
+        }
+
+        return;
+    }
+
+    // impossible event type
+    unreachable;
+}
+
+// Exists to skip the checks made _observe when called from a DOMNodeInserted
+// event. In such events, the event handler has alread done the necessary
+// checks.
+fn forceObserve(self: *IntersectionObserver, target: *parser.Element) !void {
+    try self.observed_entries.append(self.page.arena, .{
+        .page = self.page,
+        .root = self.root,
+        .target = target,
+    });
+
+    var result: js.Function.Result = undefined;
+    self.callback.tryCall(void, .{self.observed_entries.items}, &result) catch {
+        log.debug(.user_script, "callback error", .{
+            .err = result.exception,
+            .stack = result.stack,
+            .source = "intersection observer",
+        });
+    };
+}
+
+fn removeObserved(self: *IntersectionObserver, target: *parser.Element) bool {
+    for (self.observed_entries.items, 0..) |*observer, index| {
+        if (observer.target == target) {
+            _ = self.observed_entries.swapRemove(index);
+            return true;
+        }
+    }
+    return false;
+}
+
+fn removePending(self: *IntersectionObserver, target: *parser.Element) bool {
+    for (self.pending_elements.items, 0..) |el, index| {
+        if (el == target) {
+            _ = self.pending_elements.swapRemove(index);
+            return true;
+        }
+    }
+    return false;
+}
+
+const IntersectionObserverOptions = struct {
+    root: ?*parser.Node = null, // Element or Document
+    rootMargin: ?[]const u8 = "0px 0px 0px 0px",
+    threshold: ?Threshold = .{ .single = 0.0 },
+
+    const Threshold = union(enum) {
+        single: f32,
+        list: []const f32,
+    };
+};
+
+// https://developer.mozilla.org/en-US/docs/Web/API/Entry
+// https://w3c.github.io/IntersectionObserver/#intersection-observer-entry
+pub const Entry = struct {
+    page: *Page,
+    root: *parser.Node,
+    target: *parser.Element,
+
+    // Returns the bounds rectangle of the target element as a DOMRectReadOnly. The bounds are computed as described in the documentation for Element.getBoundingClientRect().
+    pub fn get_boundingClientRect(self: *const Entry) !Element.DOMRect {
+        return Element._getBoundingClientRect(self.target, self.page);
+    }
+
+    // Returns the ratio of the intersectionRect to the boundingClientRect.
+    pub fn get_intersectionRatio(_: *const Entry) f32 {
+        return 1.0;
+    }
+
+    // Returns a DOMRectReadOnly representing the target's visible area.
+    pub fn get_intersectionRect(self: *const Entry) !Element.DOMRect {
+        return Element._getBoundingClientRect(self.target, self.page);
+    }
+
+    // A Boolean value which is true if the target element intersects with the
+    // intersection observer's root. If this is true, then, the
+    // Entry describes a transition into a state of
+    // intersection; if it's false, then you know the transition is from
+    // intersecting to not-intersecting.
+    pub fn get_isIntersecting(_: *const Entry) bool {
+        return true;
+    }
+
+    // Returns a DOMRectReadOnly for the intersection observer's root.
+    pub fn get_rootBounds(self: *const Entry) !Element.DOMRect {
+        const root = self.root;
+        if (@intFromPtr(root) == @intFromPtr(self.page.window.document)) {
+            return self.page.renderer.boundingRect();
+        }
+
+        const root_type = parser.nodeType(root);
+
+        var element: *parser.Element = undefined;
+        switch (root_type) {
+            .element => element = parser.nodeToElement(root),
+            .document => {
+                const doc = parser.nodeToDocument(root);
+                element = (try parser.documentGetDocumentElement(doc)).?;
+            },
+            else => return error.InvalidState,
+        }
+
+        return Element._getBoundingClientRect(element, self.page);
+    }
+
+    // The Element whose intersection with the root changed.
+    pub fn get_target(self: *const Entry) *parser.Element {
+        return self.target;
+    }
+
+    // TODO: pub fn get_time(self: *const Entry)
+};
+
+const testing = @import("../../testing.zig");
+test "Browser: DOM.IntersectionObserver" {
+    try testing.htmlRunner("dom/intersection_observer.html");
+}

src/browser/dom/MessageChannel.zig

@@ -20,13 +20,11 @@ const std = @import("std");
 const log = @import("../../log.zig");
 const parser = @import("../netsurf.zig");
 
-const Env = @import("../env.zig").Env;
+const js = @import("../js/js.zig");
 const Page = @import("../page.zig").Page;
 const EventTarget = @import("../dom/event_target.zig").EventTarget;
 const EventHandler = @import("../events/event.zig").EventHandler;
 
-const JsObject = Env.JsObject;
-const Function = Env.Function;
 const Allocator = std.mem.Allocator;
 
 const MAX_QUEUE_SIZE = 10;
@@ -72,29 +70,28 @@ pub const MessagePort = struct {
     pair: *MessagePort,
     closed: bool = false,
     started: bool = false,
-    onmessage_cbk: ?Function = null,
-    onmessageerror_cbk: ?Function = null,
+    onmessage_cbk: ?js.Function = null,
+    onmessageerror_cbk: ?js.Function = null,
     // This is the queue of messages to dispatch to THIS MessagePort when the
     // MessagePort is started.
-    queue: std.ArrayListUnmanaged(JsObject) = .empty,
+    queue: std.ArrayListUnmanaged(js.Object) = .empty,
 
     pub const PostMessageOption = union(enum) {
-        transfer: JsObject,
+        transfer: js.Object,
         options: Opts,
 
         pub const Opts = struct {
-            transfer: JsObject,
+            transfer: js.Object,
         };
     };
 
-    pub fn _postMessage(self: *MessagePort, obj: JsObject, opts_: ?PostMessageOption, page: *Page) !void {
+    pub fn _postMessage(self: *MessagePort, obj: js.Object, opts_: ?PostMessageOption, page: *Page) !void {
         if (self.closed) {
             return;
         }
 
         if (opts_ != null) {
             log.warn(.web_api, "not implemented", .{ .feature = "MessagePort postMessage options" });
-            return error.NotImplemented;
         }
 
         try self.pair.dispatchOrQueue(obj, page.arena);
@@ -125,10 +122,10 @@ pub const MessagePort = struct {
         self.pair.closed = true;
     }
 
-    pub fn get_onmessage(self: *MessagePort) ?Function {
+    pub fn get_onmessage(self: *MessagePort) ?js.Function {
         return self.onmessage_cbk;
     }
-    pub fn get_onmessageerror(self: *MessagePort) ?Function {
+    pub fn get_onmessageerror(self: *MessagePort) ?js.Function {
         return self.onmessageerror_cbk;
     }
 
@@ -153,7 +150,7 @@ pub const MessagePort = struct {
 
     // called from our pair. If port1.postMessage("x") is called, then this
     // will be called on port2.
-    fn dispatchOrQueue(self: *MessagePort, obj: JsObject, arena: Allocator) !void {
+    fn dispatchOrQueue(self: *MessagePort, obj: js.Object, arena: Allocator) !void {
         // our pair should have checked this already
         std.debug.assert(self.closed == false);
 
@@ -168,7 +165,7 @@ pub const MessagePort = struct {
         return self.queue.append(arena, try obj.persist());
     }
 
-    fn dispatch(self: *MessagePort, obj: JsObject) !void {
+    fn dispatch(self: *MessagePort, obj: js.Object) !void {
         // obj is already persisted, don't use `MessageEvent.constructor`, but
         // go directly to `init`, which assumes persisted objects.
         var evt = try MessageEvent.init(.{ .data = obj });
@@ -183,7 +180,7 @@ pub const MessagePort = struct {
         alloc: Allocator,
         typ: []const u8,
         listener: EventHandler.Listener,
-    ) !?Function {
+    ) !?js.Function {
         const target = @as(*parser.EventTarget, @ptrCast(self));
         const eh = (try EventHandler.register(alloc, target, typ, listener, null)) orelse unreachable;
         return eh.callback;
@@ -208,12 +205,12 @@ pub const MessageEvent = struct {
     pub const union_make_copy = true;
 
     proto: parser.Event,
-    data: ?JsObject,
+    data: ?js.Object,
 
     // You would think if port1 sends to port2, the source would be port2
     // (which is how I read the documentation), but it appears to always be
     // null. It can always be set explicitly via the constructor;
-    source: ?JsObject,
+    source: ?js.Object,
 
     origin: []const u8,
 
@@ -227,8 +224,8 @@ pub const MessageEvent = struct {
     ports: []*MessagePort,
 
     const Options = struct {
-        data: ?JsObject = null,
-        source: ?JsObject = null,
+        data: ?js.Object = null,
+        source: ?js.Object = null,
         origin: []const u8 = "",
         lastEventId: []const u8 = "",
         ports: []*MessagePort = &.{},
@@ -244,7 +241,7 @@ pub const MessageEvent = struct {
         });
     }
 
-    // This is like "constructor", but it assumes JsObjects have already been
+    // This is like "constructor", but it assumes js.Objects have already been
     // persisted. Necessary because this `new MessageEvent()` can be called
     // directly from JS OR from a port.postMessage. In the latter case, data
     // may have already been persisted (as it might need to be queued);
@@ -264,7 +261,7 @@ pub const MessageEvent = struct {
         };
     }
 
-    pub fn get_data(self: *const MessageEvent) !?JsObject {
+    pub fn get_data(self: *const MessageEvent) !?js.Object {
         return self.data;
     }
 
@@ -272,7 +269,7 @@ pub const MessageEvent = struct {
         return self.origin;
     }
 
-    pub fn get_source(self: *const MessageEvent) ?JsObject {
+    pub fn get_source(self: *const MessageEvent) ?js.Object {
         return self.source;
     }
 

src/browser/dom/attribute.zig

@@ -25,24 +25,24 @@ pub const Attr = struct {
     pub const prototype = *Node;
     pub const subtype = .node;
 
-    pub fn get_namespaceURI(self: *parser.Attribute) !?[]const u8 {
-        return try parser.nodeGetNamespace(parser.attributeToNode(self));
+    pub fn get_namespaceURI(self: *parser.Attribute) ?[]const u8 {
+        return parser.nodeGetNamespace(parser.attributeToNode(self));
     }
 
-    pub fn get_prefix(self: *parser.Attribute) !?[]const u8 {
-        return try parser.nodeGetPrefix(parser.attributeToNode(self));
+    pub fn get_prefix(self: *parser.Attribute) ?[]const u8 {
+        return parser.nodeGetPrefix(parser.attributeToNode(self));
     }
 
     pub fn get_localName(self: *parser.Attribute) ![]const u8 {
-        return try parser.nodeLocalName(parser.attributeToNode(self));
+        return parser.nodeLocalName(parser.attributeToNode(self));
     }
 
     pub fn get_name(self: *parser.Attribute) ![]const u8 {
-        return try parser.attributeGetName(self);
+        return parser.attributeGetName(self);
     }
 
     pub fn get_value(self: *parser.Attribute) !?[]const u8 {
-        return try parser.attributeGetValue(self);
+        return parser.attributeGetValue(self);
     }
 
     pub fn set_value(self: *parser.Attribute, v: []const u8) !?[]const u8 {

src/browser/dom/character_data.zig

@@ -51,7 +51,7 @@ pub const CharacterData = struct {
     }
 
     pub fn get_nextElementSibling(self: *parser.CharacterData) !?ElementUnion {
-        const res = try parser.nodeNextElementSibling(parser.characterDataToNode(self));
+        const res = parser.nodeNextElementSibling(parser.characterDataToNode(self));
         if (res == null) {
             return null;
         }
@@ -59,7 +59,7 @@ pub const CharacterData = struct {
     }
 
     pub fn get_previousElementSibling(self: *parser.CharacterData) !?ElementUnion {
-        const res = try parser.nodePreviousElementSibling(parser.characterDataToNode(self));
+        const res = parser.nodePreviousElementSibling(parser.characterDataToNode(self));
         if (res == null) {
             return null;
         }
@@ -68,8 +68,8 @@ pub const CharacterData = struct {
 
     // Read/Write attributes
 
-    pub fn get_data(self: *parser.CharacterData) ![]const u8 {
-        return try parser.characterDataData(self);
+    pub fn get_data(self: *parser.CharacterData) []const u8 {
+        return parser.characterDataData(self);
     }
 
     pub fn set_data(self: *parser.CharacterData, data: []const u8) !void {
@@ -96,18 +96,18 @@ pub const CharacterData = struct {
     }
 
     pub fn _substringData(self: *parser.CharacterData, offset: u32, count: u32) ![]const u8 {
-        return try parser.characterDataSubstringData(self, offset, count);
+        return parser.characterDataSubstringData(self, offset, count);
     }
 
     // netsurf's CharacterData (text, comment) doesn't implement the
     // dom_node_get_attributes and thus will crash if we try to call nodeIsEqualNode.
-    pub fn _isEqualNode(self: *parser.CharacterData, other_node: *parser.Node) !bool {
-        if (try parser.nodeType(@ptrCast(@alignCast(self))) != try parser.nodeType(other_node)) {
+    pub fn _isEqualNode(self: *parser.CharacterData, other_node: *parser.Node) bool {
+        if (parser.nodeType(@ptrCast(@alignCast(self))) != parser.nodeType(other_node)) {
             return false;
         }
 
         const other: *parser.CharacterData = @ptrCast(other_node);
-        if (std.mem.eql(u8, try get_data(self), try get_data(other)) == false) {
+        if (std.mem.eql(u8, get_data(self), get_data(other)) == false) {
             return false;
         }
 

src/browser/dom/document.zig

@@ -17,8 +17,9 @@
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 const std = @import("std");
-
 const log = @import("../../log.zig");
+
+const js = @import("../js/js.zig");
 const parser = @import("../netsurf.zig");
 const Page = @import("../page.zig").Page;
 
@@ -38,8 +39,6 @@ const Range = @import("range.zig").Range;
 
 const CustomEvent = @import("../events/custom_event.zig").CustomEvent;
 
-const Env = @import("../env.zig").Env;
-
 const DOMImplementation = @import("implementation.zig").DOMImplementation;
 
 // WEB IDL https://dom.spec.whatwg.org/#document
@@ -156,22 +155,14 @@ pub const Document = struct {
     // the spec changed to return an HTMLCollection instead.
     // That's why we reimplemented getElementsByTagName by using an
     // HTMLCollection in zig here.
-    pub fn _getElementsByTagName(
-        self: *parser.Document,
-        tag_name: []const u8,
-        page: *Page,
-    ) !collection.HTMLCollection {
-        return try collection.HTMLCollectionByTagName(page.arena, parser.documentToNode(self), tag_name, .{
+    pub fn _getElementsByTagName(self: *parser.Document, tag_name: js.String) !collection.HTMLCollection {
+        return collection.HTMLCollectionByTagName(parser.documentToNode(self), tag_name.string, .{
             .include_root = true,
         });
     }
 
-    pub fn _getElementsByClassName(
-        self: *parser.Document,
-        classNames: []const u8,
-        page: *Page,
-    ) !collection.HTMLCollection {
-        return try collection.HTMLCollectionByClassName(page.arena, parser.documentToNode(self), classNames, .{
+    pub fn _getElementsByClassName(self: *parser.Document, class_names: js.String) !collection.HTMLCollection {
+        return collection.HTMLCollectionByClassName(parser.documentToNode(self), class_names.string, .{
             .include_root = true,
         });
     }
@@ -308,21 +299,26 @@ pub const Document = struct {
         return &.{};
     }
 
-    pub fn get_adoptedStyleSheets(self: *parser.Document, page: *Page) !Env.JsObject {
+    pub fn get_adoptedStyleSheets(self: *parser.Document, page: *Page) !js.Object {
         const state = try page.getOrCreateNodeState(@ptrCast(@alignCast(self)));
         if (state.adopted_style_sheets) |obj| {
             return obj;
         }
 
-        const obj = try page.main_context.newArray(0).persist();
+        const obj = try page.js.createArray(0).persist();
         state.adopted_style_sheets = obj;
         return obj;
     }
 
-    pub fn set_adoptedStyleSheets(self: *parser.Document, sheets: Env.JsObject, page: *Page) !void {
+    pub fn set_adoptedStyleSheets(self: *parser.Document, sheets: js.Object, page: *Page) !void {
         const state = try page.getOrCreateNodeState(@ptrCast(@alignCast(self)));
         state.adopted_style_sheets = try sheets.persist();
     }
+
+    pub fn _hasFocus(_: *parser.Document) bool {
+        log.debug(.web_api, "not implemented", .{ .feature = "Document hasFocus" });
+        return true;
+    }
 };
 
 const testing = @import("../../testing.zig");

src/browser/dom/document_fragment.zig

@@ -38,8 +38,8 @@ pub const DocumentFragment = struct {
         );
     }
 
-    pub fn _isEqualNode(self: *parser.DocumentFragment, other_node: *parser.Node) !bool {
-        const other_type = try parser.nodeType(other_node);
+    pub fn _isEqualNode(self: *parser.DocumentFragment, other_node: *parser.Node) bool {
+        const other_type = parser.nodeType(other_node);
         if (other_type != .document_fragment) {
             return false;
         }

src/browser/dom/document_type.zig

@@ -29,21 +29,21 @@ pub const DocumentType = struct {
     pub const subtype = .node;
 
     pub fn get_name(self: *parser.DocumentType) ![]const u8 {
-        return try parser.documentTypeGetName(self);
+        return parser.documentTypeGetName(self);
     }
 
-    pub fn get_publicId(self: *parser.DocumentType) ![]const u8 {
-        return try parser.documentTypeGetPublicId(self);
+    pub fn get_publicId(self: *parser.DocumentType) []const u8 {
+        return parser.documentTypeGetPublicId(self);
     }
 
-    pub fn get_systemId(self: *parser.DocumentType) ![]const u8 {
-        return try parser.documentTypeGetSystemId(self);
+    pub fn get_systemId(self: *parser.DocumentType) []const u8 {
+        return parser.documentTypeGetSystemId(self);
     }
 
     // netsurf's DocumentType doesn't implement the dom_node_get_attributes
     // and thus will crash if we try to call nodeIsEqualNode.
     pub fn _isEqualNode(self: *parser.DocumentType, other_node: *parser.Node) !bool {
-        if (try parser.nodeType(other_node) != .document_type) {
+        if (parser.nodeType(other_node) != .document_type) {
             return false;
         }
 
@@ -51,10 +51,10 @@ pub const DocumentType = struct {
         if (std.mem.eql(u8, try get_name(self), try get_name(other)) == false) {
             return false;
         }
-        if (std.mem.eql(u8, try get_publicId(self), try get_publicId(other)) == false) {
+        if (std.mem.eql(u8, get_publicId(self), get_publicId(other)) == false) {
             return false;
         }
-        if (std.mem.eql(u8, try get_systemId(self), try get_systemId(other)) == false) {
+        if (std.mem.eql(u8, get_systemId(self), get_systemId(other)) == false) {
             return false;
         }
         return true;

src/browser/dom/dom.zig

@@ -25,7 +25,6 @@ const NodeList = @import("nodelist.zig");
 const Node = @import("node.zig");
 const ResizeObserver = @import("resize_observer.zig");
 const MutationObserver = @import("mutation_observer.zig");
-const IntersectionObserver = @import("intersection_observer.zig");
 const DOMParser = @import("dom_parser.zig").DOMParser;
 const TreeWalker = @import("tree_walker.zig").TreeWalker;
 const NodeIterator = @import("node_iterator.zig").NodeIterator;
@@ -44,7 +43,6 @@ pub const Interfaces = .{
     Node.Interfaces,
     ResizeObserver.Interfaces,
     MutationObserver.Interfaces,
-    IntersectionObserver.Interfaces,
     DOMParser,
     TreeWalker,
     NodeIterator,
@@ -54,4 +52,5 @@ pub const Interfaces = .{
     @import("range.zig").Interfaces,
     @import("Animation.zig"),
     @import("MessageChannel.zig").Interfaces,
+    @import("IntersectionObserver.zig").Interfaces,
 };

src/browser/dom/element.zig

@@ -18,6 +18,7 @@
 
 const std = @import("std");
 
+const js = @import("../js/js.zig");
 const parser = @import("../netsurf.zig");
 const Page = @import("../page.zig").Page;
 
@@ -33,7 +34,6 @@ const HTMLElem = @import("../html/elements.zig");
 const ShadowRoot = @import("../dom/shadow_root.zig").ShadowRoot;
 
 const Animation = @import("Animation.zig");
-const JsObject = @import("../env.zig").JsObject;
 
 pub const Union = @import("../html/elements.zig").Union;
 
@@ -61,7 +61,7 @@ pub const Element = struct {
     pub fn toInterfaceT(comptime T: type, e: *parser.Element) !T {
         const tagname = try parser.elementGetTagName(e) orelse {
             // If the owner's document is HTML, assume we have an HTMLElement.
-            const doc = try parser.nodeOwnerDocument(parser.elementToNode(e));
+            const doc = parser.nodeOwnerDocument(parser.elementToNode(e));
             if (doc != null and !doc.?.is_html) {
                 return .{ .HTMLElement = @as(*parser.ElementHTML, @ptrCast(e)) };
             }
@@ -73,7 +73,7 @@ pub const Element = struct {
 
         const tag = parser.Tag.fromString(tagname) catch {
             // If the owner's document is HTML, assume we have an HTMLElement.
-            const doc = try parser.nodeOwnerDocument(parser.elementToNode(e));
+            const doc = parser.nodeOwnerDocument(parser.elementToNode(e));
             if (doc != null and doc.?.is_html) {
                 return .{ .HTMLElement = @as(*parser.ElementHTML, @ptrCast(e)) };
             }
@@ -87,12 +87,12 @@ pub const Element = struct {
     // JS funcs
     // --------
 
-    pub fn get_namespaceURI(self: *parser.Element) !?[]const u8 {
-        return try parser.nodeGetNamespace(parser.elementToNode(self));
+    pub fn get_namespaceURI(self: *parser.Element) ?[]const u8 {
+        return parser.nodeGetNamespace(parser.elementToNode(self));
     }
 
-    pub fn get_prefix(self: *parser.Element) !?[]const u8 {
-        return try parser.nodeGetPrefix(parser.elementToNode(self));
+    pub fn get_prefix(self: *parser.Element) ?[]const u8 {
+        return parser.nodeGetPrefix(parser.elementToNode(self));
     }
 
     pub fn get_localName(self: *parser.Element) ![]const u8 {
@@ -103,6 +103,14 @@ pub const Element = struct {
         return try parser.nodeName(parser.elementToNode(self));
     }
 
+    pub fn get_dir(self: *parser.Element) ![]const u8 {
+        return try parser.elementGetAttribute(self, "dir") orelse "";
+    }
+
+    pub fn set_dir(self: *parser.Element, dir: []const u8) !void {
+        return parser.elementSetAttribute(self, "dir", dir);
+    }
+
     pub fn get_id(self: *parser.Element) ![]const u8 {
         return try parser.elementGetAttribute(self, "id") orelse "";
     }
@@ -127,6 +135,10 @@ pub const Element = struct {
         return try parser.elementSetAttribute(self, "slot", slot);
     }
 
+    pub fn get_assignedSlot(self: *parser.Element, page: *const Page) !?*parser.Slot {
+        return @import("../SlotChangeMonitor.zig").findSlot(self, page);
+    }
+
     pub fn get_classList(self: *parser.Element) !*parser.TokenList {
         return try parser.tokenListCreate(self, "class");
     }
@@ -150,7 +162,7 @@ pub const Element = struct {
 
     pub fn set_innerHTML(self: *parser.Element, str: []const u8, page: *Page) !void {
         const node = parser.elementToNode(self);
-        const doc = try parser.nodeOwnerDocument(node) orelse return parser.DOMError.WrongDocument;
+        const doc = parser.nodeOwnerDocument(node) orelse return parser.DOMError.WrongDocument;
         // parse the fragment
         const fragment = try parser.documentParseFragmentFromStr(doc, str);
 
@@ -168,9 +180,9 @@ pub const Element = struct {
         // or an actual document. In a blank page, something like:
         //    x.innerHTML = '<script></script>';
         // does _not_ create an empty script, but in a real page, it does. Weird.
-        const html = try parser.nodeFirstChild(fragment_node) orelse return;
-        const head = try parser.nodeFirstChild(html) orelse return;
-        const body = try parser.nodeNextSibling(head) orelse return;
+        const html = parser.nodeFirstChild(fragment_node) orelse return;
+        const head = parser.nodeFirstChild(html) orelse return;
+        const body = parser.nodeNextSibling(head) orelse return;
 
         if (try parser.elementTag(self) == .template) {
             // HTMLElementTemplate is special. We don't append these as children
@@ -179,11 +191,9 @@ pub const Element = struct {
             // a new fragment
             const clean = try parser.documentCreateDocumentFragment(doc);
             const children = try parser.nodeGetChildNodes(body);
-            const ln = try parser.nodeListLength(children);
-            for (0..ln) |_| {
-                // always index 0, because nodeAppendChild moves the node out of
-                // the nodeList and into the new tree
-                const child = try parser.nodeListItem(children, 0) orelse continue;
+            // always index 0, because nodeAppendChild moves the node out of
+            // the nodeList and into the new tree
+            while (parser.nodeListItem(children, 0)) |child| {
                 _ = try parser.nodeAppendChild(@ptrCast(@alignCast(clean)), child);
             }
 
@@ -197,27 +207,102 @@ pub const Element = struct {
         {
             // First, copy some of the head element
             const children = try parser.nodeGetChildNodes(head);
-            const ln = try parser.nodeListLength(children);
-            for (0..ln) |_| {
-                // always index 0, because nodeAppendChild moves the node out of
-                // the nodeList and into the new tree
-                const child = try parser.nodeListItem(children, 0) orelse continue;
+            // always index 0, because nodeAppendChild moves the node out of
+            // the nodeList and into the new tree
+            while (parser.nodeListItem(children, 0)) |child| {
                 _ = try parser.nodeAppendChild(node, child);
             }
         }
 
         {
             const children = try parser.nodeGetChildNodes(body);
-            const ln = try parser.nodeListLength(children);
-            for (0..ln) |_| {
-                // always index 0, because nodeAppendChild moves the node out of
-                // the nodeList and into the new tree
-                const child = try parser.nodeListItem(children, 0) orelse continue;
+            // always index 0, because nodeAppendChild moves the node out of
+            // the nodeList and into the new tree
+            while (parser.nodeListItem(children, 0)) |child| {
                 _ = try parser.nodeAppendChild(node, child);
             }
         }
     }
 
+    /// Parses the given `input` string and inserts its children to an element at given `position`.
+    /// https://developer.mozilla.org/en-US/docs/Web/API/Element/insertAdjacentHTML
+    ///
+    /// TODO: Support for XML parsing and `TrustedHTML` instances.
+    pub fn _insertAdjacentHTML(self: *parser.Element, position: []const u8, input: []const u8) !void {
+        const self_node = parser.elementToNode(self);
+        const doc = parser.nodeOwnerDocument(self_node) orelse {
+            return parser.DOMError.WrongDocument;
+        };
+
+        // Parse the fragment.
+        // Should return error.Syntax on fail?
+        const fragment = try parser.documentParseFragmentFromStr(doc, input);
+        const fragment_node = parser.documentFragmentToNode(fragment);
+
+        // We always get it wrapped like so:
+        // <html><head></head><body>{ ... }</body></html>
+        // None of the following can be null.
+        const maybe_html = parser.nodeFirstChild(fragment_node);
+        std.debug.assert(maybe_html != null);
+        const html = maybe_html orelse return;
+
+        const maybe_body = parser.nodeLastChild(html);
+        std.debug.assert(maybe_body != null);
+        const body = maybe_body orelse return;
+
+        const children = try parser.nodeGetChildNodes(body);
+
+        // * `target_node` is `*Node` (where we actually insert),
+        // * `prev_node` is `?*Node`.
+        const target_node, const prev_node = blk: {
+            // Prefer case-sensitive match.
+            // "beforeend" was the most common case in my tests; we might adjust the order
+            // depending on which ones websites prefer most.
+            if (std.mem.eql(u8, position, "beforeend")) {
+                break :blk .{ self_node, null };
+            }
+
+            if (std.mem.eql(u8, position, "afterbegin")) {
+                // Get the first child; null indicates there are no children.
+                const first_child = parser.nodeFirstChild(self_node);
+                break :blk .{ self_node, first_child };
+            }
+
+            if (std.mem.eql(u8, position, "beforebegin")) {
+                // The node must have a parent node in order to use this variant.
+                const parent = parser.nodeParentNode(self_node) orelse return error.NoModificationAllowed;
+                // Parent cannot be Document.
+                // Should have checks for document_fragment and document_type?
+                if (parser.nodeType(parent) == .document) {
+                    return error.NoModificationAllowed;
+                }
+
+                break :blk .{ parent, self_node };
+            }
+
+            if (std.mem.eql(u8, position, "afterend")) {
+                // The node must have a parent node in order to use this variant.
+                const parent = parser.nodeParentNode(self_node) orelse return error.NoModificationAllowed;
+                // Parent cannot be Document.
+                if (parser.nodeType(parent) == .document) {
+                    return error.NoModificationAllowed;
+                }
+                // Get the next sibling or null; null indicates our node is the only one.
+                const sibling = parser.nodeNextSibling(self_node);
+                break :blk .{ parent, sibling };
+            }
+
+            // Thrown if:
+            // * position is not one of the four listed values.
+            // * The input is XML that is not well-formed.
+            return error.Syntax;
+        };
+
+        while (parser.nodeListItem(children, 0)) |child| {
+            _ = try parser.nodeInsertBefore(target_node, child, prev_node);
+        }
+    }
+
     // The closest() method of the Element interface traverses the element and its parents (heading toward the document root) until it finds a node that matches the specified CSS selector.
     // Returns the closest ancestor Element or itself, which matches the selectors. If there are no such element, null.
     pub fn _closest(self: *parser.Element, selector: []const u8, page: *Page) !?*parser.Element {
@@ -234,7 +319,7 @@ pub const Element = struct {
                 }
                 return parser.nodeToElement(current.node);
             }
-            current = try current.parent() orelse return null;
+            current = current.parent() orelse return null;
         }
     }
 
@@ -350,28 +435,18 @@ pub const Element = struct {
         return try parser.elementRemoveAttributeNode(self, attr);
     }
 
-    pub fn _getElementsByTagName(
-        self: *parser.Element,
-        tag_name: []const u8,
-        page: *Page,
-    ) !collection.HTMLCollection {
-        return try collection.HTMLCollectionByTagName(
-            page.arena,
+    pub fn _getElementsByTagName(self: *parser.Element, tag_name: js.String) !collection.HTMLCollection {
+        return collection.HTMLCollectionByTagName(
             parser.elementToNode(self),
-            tag_name,
+            tag_name.string,
             .{ .include_root = false },
         );
     }
 
-    pub fn _getElementsByClassName(
-        self: *parser.Element,
-        classNames: []const u8,
-        page: *Page,
-    ) !collection.HTMLCollection {
+    pub fn _getElementsByClassName(self: *parser.Element, class_names: js.String) !collection.HTMLCollection {
         return try collection.HTMLCollectionByClassName(
-            page.arena,
             parser.elementToNode(self),
-            classNames,
+            class_names.string,
             .{ .include_root = false },
         );
     }
@@ -407,13 +482,13 @@ pub const Element = struct {
     // NonDocumentTypeChildNode
     // https://dom.spec.whatwg.org/#interface-nondocumenttypechildnode
     pub fn get_previousElementSibling(self: *parser.Element) !?Union {
-        const res = try parser.nodePreviousElementSibling(parser.elementToNode(self));
+        const res = parser.nodePreviousElementSibling(parser.elementToNode(self));
         if (res == null) return null;
         return try toInterface(res.?);
     }
 
     pub fn get_nextElementSibling(self: *parser.Element) !?Union {
-        const res = try parser.nodeNextElementSibling(parser.elementToNode(self));
+        const res = parser.nodeNextElementSibling(parser.elementToNode(self));
         if (res == null) return null;
         return try toInterface(res.?);
     }
@@ -426,7 +501,7 @@ pub const Element = struct {
         while (true) {
             next = try walker.get_next(root, next) orelse return null;
             // ignore non-element nodes.
-            if (try parser.nodeType(next.?) != .element) {
+            if (parser.nodeType(next.?) != .element) {
                 continue;
             }
             const e = parser.nodeToElement(next.?);
@@ -474,7 +549,7 @@ pub const Element = struct {
     // Returns a 0 DOMRect object if the element is eventually detached from the main window
     pub fn _getBoundingClientRect(self: *parser.Element, page: *Page) !DOMRect {
         // Since we are lazy rendering we need to do this check. We could store the renderer in a viewport such that it could cache these, but it would require tracking changes.
-        if (!try page.isNodeAttached(parser.elementToNode(self))) {
+        if (!page.isNodeAttached(parser.elementToNode(self))) {
             return DOMRect{
                 .x = 0,
                 .y = 0,
@@ -493,7 +568,7 @@ pub const Element = struct {
     // We do not render so it only always return the element's bounding rect.
     // Returns an empty array if the element is eventually detached from the main window
     pub fn _getClientRects(self: *parser.Element, page: *Page) ![]DOMRect {
-        if (!try page.isNodeAttached(parser.elementToNode(self))) {
+        if (!page.isNodeAttached(parser.elementToNode(self))) {
             return &.{};
         }
         const heap_ptr = try page.call_arena.create(DOMRect);
@@ -524,6 +599,8 @@ pub const Element = struct {
         contentVisibilityAuto: bool,
         opacityProperty: bool,
         visibilityProperty: bool,
+        checkVisibilityCSS: bool,
+        checkOpacity: bool,
     };
 
     pub fn _checkVisibility(self: *parser.Element, opts: ?CheckVisibilityOpts) bool {
@@ -549,7 +626,7 @@ pub const Element = struct {
         }
 
         // Not sure what to do if there is no owner document
-        const doc = try parser.nodeOwnerDocument(@ptrCast(self)) orelse return error.InvalidArgument;
+        const doc = parser.nodeOwnerDocument(@ptrCast(self)) orelse return error.InvalidArgument;
         const fragment = try parser.documentCreateDocumentFragment(doc);
         const sr = try page.arena.create(ShadowRoot);
         sr.* = .{
@@ -583,7 +660,7 @@ pub const Element = struct {
         return sr;
     }
 
-    pub fn _animate(self: *parser.Element, effect: JsObject, opts: JsObject) !Animation {
+    pub fn _animate(self: *parser.Element, effect: js.Object, opts: js.Object) !Animation {
         _ = self;
         _ = opts;
         return Animation.constructor(effect, null);
@@ -595,7 +672,7 @@ pub const Element = struct {
         // for related elements JIT by walking the tree, but there could be
         // cases in libdom or the Zig WebAPI where this reference is kept
         const as_node: *parser.Node = @ptrCast(self);
-        const parent = try parser.nodeParentNode(as_node) orelse return;
+        const parent = parser.nodeParentNode(as_node) orelse return;
         _ = try Node._removeChild(parent, as_node);
     }
 };

src/browser/dom/event_target.zig

@@ -17,7 +17,6 @@
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 const std = @import("std");
-const Env = @import("../env.zig").Env;
 const parser = @import("../netsurf.zig");
 const Page = @import("../page.zig").Page;
 
@@ -48,7 +47,7 @@ pub const EventTarget = struct {
     pub fn toInterface(et: *parser.EventTarget, page: *Page) !Union {
         // libdom assumes that all event targets are libdom nodes. They are not.
 
-        switch (try parser.eventTargetInternalType(et)) {
+        switch (parser.eventTargetInternalType(et)) {
             .libdom_node => {
                 return .{ .node = try nod.Node.toInterface(@as(*parser.Node, @ptrCast(et))) };
             },
@@ -101,6 +100,9 @@ pub const EventTarget = struct {
         page: *Page,
     ) !void {
         _ = try EventHandler.register(page.arena, self, typ, listener, opts);
+        if (std.mem.eql(u8, typ, "slotchange")) {
+            try page.registerSlotChangeMonitor();
+        }
     }
 
     const RemoveEventListenerOpts = union(enum) {

src/browser/dom/html_collection.zig

@@ -23,7 +23,6 @@ const parser = @import("../netsurf.zig");
 
 const Element = @import("element.zig").Element;
 const Union = @import("element.zig").Union;
-const JsThis = @import("../env.zig").JsThis;
 const Walker = @import("walker.zig").Walker;
 
 const Matcher = union(enum) {
@@ -52,13 +51,13 @@ pub const MatchByTagName = struct {
     tag: []const u8,
     is_wildcard: bool,
 
-    fn init(arena: Allocator, tag_name: []const u8) !MatchByTagName {
+    fn init(tag_name: []const u8) MatchByTagName {
         if (std.mem.eql(u8, tag_name, "*")) {
             return .{ .tag = "*", .is_wildcard = true };
         }
 
         return .{
-            .tag = try arena.dupe(u8, tag_name),
+            .tag = tag_name,
             .is_wildcard = false,
         };
     }
@@ -69,15 +68,14 @@ pub const MatchByTagName = struct {
 };
 
 pub fn HTMLCollectionByTagName(
-    arena: Allocator,
     root: ?*parser.Node,
     tag_name: []const u8,
     opts: Opts,
-) !HTMLCollection {
-    return HTMLCollection{
+) HTMLCollection {
+    return .{
         .root = root,
         .walker = .{ .walkerDepthFirst = .{} },
-        .matcher = .{ .matchByTagName = try MatchByTagName.init(arena, tag_name) },
+        .matcher = .{ .matchByTagName = MatchByTagName.init(tag_name) },
         .mutable = opts.mutable,
         .include_root = opts.include_root,
     };
@@ -86,9 +84,9 @@ pub fn HTMLCollectionByTagName(
 pub const MatchByClassName = struct {
     class_names: []const u8,
 
-    fn init(arena: Allocator, class_names: []const u8) !MatchByClassName {
+    fn init(class_names: []const u8) !MatchByClassName {
         return .{
-            .class_names = try arena.dupe(u8, class_names),
+            .class_names = class_names,
         };
     }
 
@@ -107,15 +105,14 @@ pub const MatchByClassName = struct {
 };
 
 pub fn HTMLCollectionByClassName(
-    arena: Allocator,
     root: ?*parser.Node,
-    classNames: []const u8,
+    class_names: []const u8,
     opts: Opts,
 ) !HTMLCollection {
     return HTMLCollection{
         .root = root,
         .walker = .{ .walkerDepthFirst = .{} },
-        .matcher = .{ .matchByClassName = try MatchByClassName.init(arena, classNames) },
+        .matcher = .{ .matchByClassName = try MatchByClassName.init(class_names) },
         .mutable = opts.mutable,
         .include_root = opts.include_root,
     };
@@ -124,10 +121,8 @@ pub fn HTMLCollectionByClassName(
 pub const MatchByName = struct {
     name: []const u8,
 
-    fn init(arena: Allocator, name: []const u8) !MatchByName {
-        return .{
-            .name = try arena.dupe(u8, name),
-        };
+    fn init(name: []const u8) !MatchByName {
+        return .{ .name = name };
     }
 
     pub fn match(self: MatchByName, node: *parser.Node) !bool {
@@ -138,7 +133,6 @@ pub const MatchByName = struct {
 };
 
 pub fn HTMLCollectionByName(
-    arena: Allocator,
     root: ?*parser.Node,
     name: []const u8,
     opts: Opts,
@@ -146,7 +140,7 @@ pub fn HTMLCollectionByName(
     return HTMLCollection{
         .root = root,
         .walker = .{ .walkerDepthFirst = .{} },
-        .matcher = .{ .matchByName = try MatchByName.init(arena, name) },
+        .matcher = .{ .matchByName = try MatchByName.init(name) },
         .mutable = opts.mutable,
         .include_root = opts.include_root,
     };
@@ -203,8 +197,8 @@ pub fn HTMLCollectionChildren(
     };
 }
 
-pub fn HTMLCollectionEmpty() !HTMLCollection {
-    return HTMLCollection{
+pub fn HTMLCollectionEmpty() HTMLCollection {
+    return .{
         .root = null,
         .walker = .{ .walkerNone = .{} },
         .matcher = .{ .matchFalse = .{} },
@@ -226,14 +220,11 @@ pub const MatchByLinks = struct {
     }
 };
 
-pub fn HTMLCollectionByLinks(
-    root: ?*parser.Node,
-    opts: Opts,
-) !HTMLCollection {
-    return HTMLCollection{
+pub fn HTMLCollectionByLinks(root: ?*parser.Node, opts: Opts) HTMLCollection {
+    return .{
         .root = root,
         .walker = .{ .walkerDepthFirst = .{} },
-        .matcher = .{ .matchByLinks = MatchByLinks{} },
+        .matcher = .{ .matchByLinks = .{} },
         .mutable = opts.mutable,
         .include_root = opts.include_root,
     };
@@ -252,14 +243,11 @@ pub const MatchByAnchors = struct {
     }
 };
 
-pub fn HTMLCollectionByAnchors(
-    root: ?*parser.Node,
-    opts: Opts,
-) !HTMLCollection {
-    return HTMLCollection{
+pub fn HTMLCollectionByAnchors(root: ?*parser.Node, opts: Opts) HTMLCollection {
+    return .{
         .root = root,
         .walker = .{ .walkerDepthFirst = .{} },
-        .matcher = .{ .matchByAnchors = MatchByAnchors{} },
+        .matcher = .{ .matchByAnchors = .{} },
         .mutable = opts.mutable,
         .include_root = opts.include_root,
     };
@@ -298,7 +286,7 @@ const Opts = struct {
 
 // WEB IDL https://dom.spec.whatwg.org/#htmlcollection
 // HTMLCollection is re implemented in zig here because libdom
-// dom_html_collection expects a comparison function callback as arguement.
+// dom_html_collection expects a comparison function callback as argument.
 // But we wanted a dynamically comparison here, according to the match tagname.
 pub const HTMLCollection = struct {
     matcher: Matcher,
@@ -344,7 +332,7 @@ pub const HTMLCollection = struct {
         var node = try self.start() orelse return 0;
 
         while (true) {
-            if (try parser.nodeType(node) == .element) {
+            if (parser.nodeType(node) == .element) {
                 if (try self.matcher.match(node)) {
                     len += 1;
                 }
@@ -371,7 +359,7 @@ pub const HTMLCollection = struct {
         }
 
         while (true) {
-            if (try parser.nodeType(node) == .element) {
+            if (parser.nodeType(node) == .element) {
                 if (try self.matcher.match(node)) {
                     // check if we found the searched element.
                     if (i == index) {
@@ -405,7 +393,7 @@ pub const HTMLCollection = struct {
         var node = try self.start() orelse return null;
 
         while (true) {
-            if (try parser.nodeType(node) == .element) {
+            if (parser.nodeType(node) == .element) {
                 if (try self.matcher.match(node)) {
                     const elem = @as(*parser.Element, @ptrCast(node));
 
@@ -440,24 +428,23 @@ pub const HTMLCollection = struct {
         return null;
     }
 
-    pub fn postAttach(self: *HTMLCollection, js_this: JsThis) !void {
-        const len = try self.get_length();
-        for (0..len) |i| {
-            const node = try self.item(@intCast(i)) orelse unreachable;
-            const e = @as(*parser.Element, @ptrCast(node));
-            const as_interface = try Element.toInterface(e);
-            try js_this.setIndex(@intCast(i), as_interface, .{});
+    pub fn indexed_get(self: *HTMLCollection, index: u32, has_value: *bool) !?Union {
+        return (try _item(self, index)) orelse {
+            has_value.* = false;
+            return undefined;
+        };
+    }
 
-            if (try item_name(e)) |name| {
-                // Even though an entry might have an empty id, the spec says
-                // that namedItem("") should always return null
-                if (name.len > 0) {
-                    // Named fields should not be enumerable (it is defined with
-                    // the LegacyUnenumerableNamedProperties flag.)
-                    try js_this.set(name, as_interface, .{ .DONT_ENUM = true });
-                }
-            }
+    pub fn named_get(self: *const HTMLCollection, name: []const u8, has_value: *bool) !?Union {
+        // Even though an entry might have an empty id, the spec says
+        // that namedItem("") should always return null
+        if (name.len == 0) {
+            return null;
         }
+        return (try _namedItem(self, name)) orelse {
+            has_value.* = false;
+            return undefined;
+        };
     }
 };
 

src/browser/dom/intersection_observer.zig

@@ -1,186 +0,0 @@
-// Copyright (C) 2023-2025  Lightpanda (Selecy SAS)
-//
-// Francis Bouvier <francis@lightpanda.io>
-// Pierre Tachoire <pierre@lightpanda.io>
-//
-// This program is free software: you can redistribute it and/or modify
-// it under the terms of the GNU Affero General Public License as
-// published by the Free Software Foundation, either version 3 of the
-// License, or (at your option) any later version.
-//
-// This program is distributed in the hope that it will be useful,
-// but WITHOUT ANY WARRANTY; without even the implied warranty of
-// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-// GNU Affero General Public License for more details.
-//
-// You should have received a copy of the GNU Affero General Public License
-// along with this program.  If not, see <https://www.gnu.org/licenses/>.
-
-const std = @import("std");
-
-const log = @import("../../log.zig");
-const parser = @import("../netsurf.zig");
-const Page = @import("../page.zig").Page;
-
-const Env = @import("../env.zig").Env;
-const Element = @import("element.zig").Element;
-
-pub const Interfaces = .{
-    IntersectionObserver,
-    IntersectionObserverEntry,
-};
-
-// This is supposed to listen to change between the root and observation targets.
-// However, our rendered stores everything as 1 pixel sized boxes in a long row that never changes.
-// As such, there are no changes to intersections between the root and any target.
-// Instead we keep a list of all entries that are being observed.
-// The callback is called with all entries everytime a new entry is added(observed).
-// Potentially we should also call the callback at a regular interval.
-// The returned Entries are phony, they always indicate full intersection.
-// https://developer.mozilla.org/en-US/docs/Web/API/IntersectionObserver
-pub const IntersectionObserver = struct {
-    page: *Page,
-    callback: Env.Function,
-    options: IntersectionObserverOptions,
-
-    observed_entries: std.ArrayListUnmanaged(IntersectionObserverEntry),
-
-    // new IntersectionObserver(callback)
-    // new IntersectionObserver(callback, options) [not supported yet]
-    pub fn constructor(callback: Env.Function, options_: ?IntersectionObserverOptions, page: *Page) !IntersectionObserver {
-        var options = IntersectionObserverOptions{
-            .root = parser.documentToNode(parser.documentHTMLToDocument(page.window.document)),
-            .rootMargin = "0px 0px 0px 0px",
-            .threshold = .{ .single = 0.0 },
-        };
-        if (options_) |*o| {
-            if (o.root) |root| {
-                options.root = root;
-            } // Other properties are not used due to the way we render
-        }
-
-        return .{
-            .page = page,
-            .callback = callback,
-            .options = options,
-            .observed_entries = .{},
-        };
-    }
-
-    pub fn _disconnect(self: *IntersectionObserver) !void {
-        self.observed_entries = .{}; // We don't free as it is on an arena
-    }
-
-    pub fn _observe(self: *IntersectionObserver, target_element: *parser.Element) !void {
-        for (self.observed_entries.items) |*observer| {
-            if (observer.target == target_element) {
-                return; // Already observed
-            }
-        }
-
-        try self.observed_entries.append(self.page.arena, .{
-            .page = self.page,
-            .target = target_element,
-            .options = &self.options,
-        });
-
-        var result: Env.Function.Result = undefined;
-        self.callback.tryCall(void, .{self.observed_entries.items}, &result) catch {
-            log.debug(.user_script, "callback error", .{
-                .err = result.exception,
-                .stack = result.stack,
-                .source = "intersection observer",
-            });
-        };
-    }
-
-    pub fn _unobserve(self: *IntersectionObserver, target: *parser.Element) !void {
-        for (self.observed_entries.items, 0..) |*observer, index| {
-            if (observer.target == target) {
-                _ = self.observed_entries.swapRemove(index);
-                break;
-            }
-        }
-    }
-
-    pub fn _takeRecords(self: *IntersectionObserver) []IntersectionObserverEntry {
-        return self.observed_entries.items;
-    }
-};
-
-const IntersectionObserverOptions = struct {
-    root: ?*parser.Node, // Element or Document
-    rootMargin: ?[]const u8,
-    threshold: ?Threshold,
-
-    const Threshold = union(enum) {
-        single: f32,
-        list: []const f32,
-    };
-};
-
-// https://developer.mozilla.org/en-US/docs/Web/API/IntersectionObserverEntry
-// https://w3c.github.io/IntersectionObserver/#intersection-observer-entry
-pub const IntersectionObserverEntry = struct {
-    page: *Page,
-    target: *parser.Element,
-    options: *IntersectionObserverOptions,
-
-    // Returns the bounds rectangle of the target element as a DOMRectReadOnly. The bounds are computed as described in the documentation for Element.getBoundingClientRect().
-    pub fn get_boundingClientRect(self: *const IntersectionObserverEntry) !Element.DOMRect {
-        return Element._getBoundingClientRect(self.target, self.page);
-    }
-
-    // Returns the ratio of the intersectionRect to the boundingClientRect.
-    pub fn get_intersectionRatio(_: *const IntersectionObserverEntry) f32 {
-        return 1.0;
-    }
-
-    // Returns a DOMRectReadOnly representing the target's visible area.
-    pub fn get_intersectionRect(self: *const IntersectionObserverEntry) !Element.DOMRect {
-        return Element._getBoundingClientRect(self.target, self.page);
-    }
-
-    // A Boolean value which is true if the target element intersects with the
-    // intersection observer's root. If this is true, then, the
-    // IntersectionObserverEntry describes a transition into a state of
-    // intersection; if it's false, then you know the transition is from
-    // intersecting to not-intersecting.
-    pub fn get_isIntersecting(_: *const IntersectionObserverEntry) bool {
-        return true;
-    }
-
-    // Returns a DOMRectReadOnly for the intersection observer's root.
-    pub fn get_rootBounds(self: *const IntersectionObserverEntry) !Element.DOMRect {
-        const root = self.options.root.?;
-        if (@intFromPtr(root) == @intFromPtr(self.page.window.document)) {
-            return self.page.renderer.boundingRect();
-        }
-
-        const root_type = try parser.nodeType(root);
-
-        var element: *parser.Element = undefined;
-        switch (root_type) {
-            .element => element = parser.nodeToElement(root),
-            .document => {
-                const doc = parser.nodeToDocument(root);
-                element = (try parser.documentGetDocumentElement(doc)).?;
-            },
-            else => return error.InvalidState,
-        }
-
-        return Element._getBoundingClientRect(element, self.page);
-    }
-
-    // The Element whose intersection with the root changed.
-    pub fn get_target(self: *const IntersectionObserverEntry) *parser.Element {
-        return self.target;
-    }
-
-    // TODO: pub fn get_time(self: *const IntersectionObserverEntry)
-};
-
-const testing = @import("../../testing.zig");
-test "Browser: DOM.IntersectionObserver" {
-    try testing.htmlRunner("dom/intersection_observer.html");
-}

src/browser/dom/mutation_observer.zig

@@ -17,13 +17,12 @@
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 const std = @import("std");
-const Allocator = std.mem.Allocator;
 
+const js = @import("../js/js.zig");
 const log = @import("../../log.zig");
 const parser = @import("../netsurf.zig");
 const Page = @import("../page.zig").Page;
 
-const Env = @import("../env.zig").Env;
 const NodeList = @import("nodelist.zig").NodeList;
 
 pub const Interfaces = .{
@@ -36,21 +35,21 @@ const Walker = @import("../dom/walker.zig").WalkerChildren;
 // WEB IDL https://dom.spec.whatwg.org/#interface-mutationobserver
 pub const MutationObserver = struct {
     page: *Page,
-    cbk: Env.Function,
-    connected: bool,
+    cbk: js.Function,
     scheduled: bool,
+    observers: std.ArrayListUnmanaged(*Observer),
 
     // List of records which were observed. When the call scope ends, we need to
     // execute our callback with it.
     observed: std.ArrayListUnmanaged(MutationRecord),
 
-    pub fn constructor(cbk: Env.Function, page: *Page) !MutationObserver {
+    pub fn constructor(cbk: js.Function, page: *Page) !MutationObserver {
         return .{
             .cbk = cbk,
             .page = page,
             .observed = .{},
-            .connected = true,
             .scheduled = false,
+            .observers = .empty,
         };
     }
 
@@ -69,15 +68,17 @@ pub const MutationObserver = struct {
             .event_node = .{ .id = self.cbk.id, .func = Observer.handle },
         };
 
+        try self.observers.append(arena, observer);
+
         // register node's events
         if (options.childList or options.subtree) {
-            _ = try parser.eventTargetAddEventListener(
+            observer.dom_node_inserted_listener = try parser.eventTargetAddEventListener(
                 parser.toEventTarget(parser.Node, node),
                 "DOMNodeInserted",
                 &observer.event_node,
                 false,
             );
-            _ = try parser.eventTargetAddEventListener(
+            observer.dom_node_removed_listener = try parser.eventTargetAddEventListener(
                 parser.toEventTarget(parser.Node, node),
                 "DOMNodeRemoved",
                 &observer.event_node,
@@ -85,7 +86,7 @@ pub const MutationObserver = struct {
             );
         }
         if (options.attr()) {
-            _ = try parser.eventTargetAddEventListener(
+            observer.dom_node_attribute_modified_listener = try parser.eventTargetAddEventListener(
                 parser.toEventTarget(parser.Node, node),
                 "DOMAttrModified",
                 &observer.event_node,
@@ -93,7 +94,7 @@ pub const MutationObserver = struct {
             );
         }
         if (options.cdata()) {
-            _ = try parser.eventTargetAddEventListener(
+            observer.dom_cdata_modified_listener = try parser.eventTargetAddEventListener(
                 parser.toEventTarget(parser.Node, node),
                 "DOMCharacterDataModified",
                 &observer.event_node,
@@ -101,7 +102,7 @@ pub const MutationObserver = struct {
             );
         }
         if (options.subtree) {
-            _ = try parser.eventTargetAddEventListener(
+            observer.dom_subtree_modified_listener = try parser.eventTargetAddEventListener(
                 parser.toEventTarget(parser.Node, node),
                 "DOMSubtreeModified",
                 &observer.event_node,
@@ -112,10 +113,6 @@ pub const MutationObserver = struct {
 
     fn callback(ctx: *anyopaque) ?u32 {
         const self: *MutationObserver = @ptrCast(@alignCast(ctx));
-        if (self.connected == false) {
-            self.scheduled = true;
-            return null;
-        }
         self.scheduled = false;
 
         const records = self.observed.items;
@@ -125,8 +122,8 @@ pub const MutationObserver = struct {
 
         defer self.observed.clearRetainingCapacity();
 
-        var result: Env.Function.Result = undefined;
-        self.cbk.tryCall(void, .{records}, &result) catch {
+        var result: js.Function.Result = undefined;
+        self.cbk.tryCallWithThis(void, self, .{records}, &result) catch {
             log.debug(.user_script, "callback error", .{
                 .err = result.exception,
                 .stack = result.stack,
@@ -136,9 +133,55 @@ pub const MutationObserver = struct {
         return null;
     }
 
-    // TODO
     pub fn _disconnect(self: *MutationObserver) !void {
-        self.connected = false;
+        for (self.observers.items) |observer| {
+            const event_target = parser.toEventTarget(parser.Node, observer.node);
+            if (observer.dom_node_inserted_listener) |listener| {
+                try parser.eventTargetRemoveEventListener(
+                    event_target,
+                    "DOMNodeInserted",
+                    listener,
+                    false,
+                );
+            }
+
+            if (observer.dom_node_removed_listener) |listener| {
+                try parser.eventTargetRemoveEventListener(
+                    event_target,
+                    "DOMNodeRemoved",
+                    listener,
+                    false,
+                );
+            }
+
+            if (observer.dom_node_attribute_modified_listener) |listener| {
+                try parser.eventTargetRemoveEventListener(
+                    event_target,
+                    "DOMAttrModified",
+                    listener,
+                    false,
+                );
+            }
+
+            if (observer.dom_cdata_modified_listener) |listener| {
+                try parser.eventTargetRemoveEventListener(
+                    event_target,
+                    "DOMCharacterDataModified",
+                    listener,
+                    false,
+                );
+            }
+
+            if (observer.dom_subtree_modified_listener) |listener| {
+                try parser.eventTargetRemoveEventListener(
+                    event_target,
+                    "DOMSubtreeModified",
+                    listener,
+                    false,
+                );
+            }
+        }
+        self.observers.clearRetainingCapacity();
     }
 
     // TODO
@@ -223,6 +266,12 @@ const Observer = struct {
 
     event_node: parser.EventNode,
 
+    dom_node_inserted_listener: ?*parser.EventListener = null,
+    dom_node_removed_listener: ?*parser.EventListener = null,
+    dom_node_attribute_modified_listener: ?*parser.EventListener = null,
+    dom_cdata_modified_listener: ?*parser.EventListener = null,
+    dom_subtree_modified_listener: ?*parser.EventListener = null,
+
     fn appliesTo(
         self: *const Observer,
         target: *parser.Node,
@@ -284,7 +333,7 @@ const Observer = struct {
 
         const mutation_event = parser.eventToMutationEvent(event);
         const event_type = blk: {
-            const t = try parser.eventType(event);
+            const t = parser.eventType(event);
             break :blk std.meta.stringToEnum(MutationEventType, t) orelse return;
         };
 
@@ -302,12 +351,12 @@ const Observer = struct {
             .DOMAttrModified => {
                 record.attribute_name = parser.mutationEventAttributeName(mutation_event) catch null;
                 if (self.options.attributeOldValue) {
-                    record.old_value = parser.mutationEventPrevValue(mutation_event) catch null;
+                    record.old_value = parser.mutationEventPrevValue(mutation_event);
                 }
             },
             .DOMCharacterDataModified => {
                 if (self.options.characterDataOldValue) {
-                    record.old_value = parser.mutationEventPrevValue(mutation_event) catch null;
+                    record.old_value = parser.mutationEventPrevValue(mutation_event);
                 }
             },
             .DOMNodeInserted => {

src/browser/dom/node.zig

@@ -20,7 +20,7 @@ const std = @import("std");
 
 const log = @import("../../log.zig");
 const parser = @import("../netsurf.zig");
-const generate = @import("../../runtime/generate.zig");
+const generate = @import("../js/generate.zig");
 
 const Page = @import("../page.zig").Page;
 const EventTarget = @import("event_target.zig").EventTarget;
@@ -67,7 +67,7 @@ pub const Node = struct {
     pub const subtype = .node;
 
     pub fn toInterface(node: *parser.Node) !Union {
-        return switch (try parser.nodeType(node)) {
+        return switch (parser.nodeType(node)) {
             .element => try Element.toInterfaceT(
                 Union,
                 @as(*parser.Element, @ptrCast(node)),
@@ -124,7 +124,7 @@ pub const Node = struct {
     }
 
     pub fn get_firstChild(self: *parser.Node) !?Union {
-        const res = try parser.nodeFirstChild(self);
+        const res = parser.nodeFirstChild(self);
         if (res == null) {
             return null;
         }
@@ -132,7 +132,7 @@ pub const Node = struct {
     }
 
     pub fn get_lastChild(self: *parser.Node) !?Union {
-        const res = try parser.nodeLastChild(self);
+        const res = parser.nodeLastChild(self);
         if (res == null) {
             return null;
         }
@@ -140,7 +140,7 @@ pub const Node = struct {
     }
 
     pub fn get_nextSibling(self: *parser.Node) !?Union {
-        const res = try parser.nodeNextSibling(self);
+        const res = parser.nodeNextSibling(self);
         if (res == null) {
             return null;
         }
@@ -148,7 +148,7 @@ pub const Node = struct {
     }
 
     pub fn get_previousSibling(self: *parser.Node) !?Union {
-        const res = try parser.nodePreviousSibling(self);
+        const res = parser.nodePreviousSibling(self);
         if (res == null) {
             return null;
         }
@@ -156,7 +156,7 @@ pub const Node = struct {
     }
 
     pub fn get_parentNode(self: *parser.Node) !?Union {
-        const res = try parser.nodeParentNode(self);
+        const res = parser.nodeParentNode(self);
         if (res == null) {
             return null;
         }
@@ -164,7 +164,7 @@ pub const Node = struct {
     }
 
     pub fn get_parentElement(self: *parser.Node) !?ElementUnion {
-        const res = try parser.nodeParentElement(self);
+        const res = parser.nodeParentElement(self);
         if (res == null) {
             return null;
         }
@@ -176,11 +176,11 @@ pub const Node = struct {
     }
 
     pub fn get_nodeType(self: *parser.Node) !u8 {
-        return @intFromEnum(try parser.nodeType(self));
+        return @intFromEnum(parser.nodeType(self));
     }
 
     pub fn get_ownerDocument(self: *parser.Node) !?*parser.DocumentHTML {
-        const res = try parser.nodeOwnerDocument(self);
+        const res = parser.nodeOwnerDocument(self);
         if (res == null) {
             return null;
         }
@@ -190,12 +190,12 @@ pub const Node = struct {
     pub fn get_isConnected(self: *parser.Node) !bool {
         var node = self;
         while (true) {
-            const node_type = try parser.nodeType(node);
+            const node_type = parser.nodeType(node);
             if (node_type == .document) {
                 return true;
             }
 
-            if (try parser.nodeParentNode(node)) |parent| {
+            if (parser.nodeParentNode(node)) |parent| {
                 // didn't find a document, but node has a parent, let's see
                 // if it's connected;
                 node = parent;
@@ -222,15 +222,15 @@ pub const Node = struct {
     // Read/Write attributes
 
     pub fn get_nodeValue(self: *parser.Node) !?[]const u8 {
-        return try parser.nodeValue(self);
+        return parser.nodeValue(self);
     }
 
     pub fn set_nodeValue(self: *parser.Node, data: []u8) !void {
         try parser.nodeSetValue(self, data);
     }
 
-    pub fn get_textContent(self: *parser.Node) !?[]const u8 {
-        return try parser.nodeTextContent(self);
+    pub fn get_textContent(self: *parser.Node) ?[]const u8 {
+        return parser.nodeTextContent(self);
     }
 
     pub fn set_textContent(self: *parser.Node, data: []u8) !void {
@@ -240,8 +240,8 @@ pub const Node = struct {
     // Methods
 
     pub fn _appendChild(self: *parser.Node, child: *parser.Node) !Union {
-        const self_owner = try parser.nodeOwnerDocument(self);
-        const child_owner = try parser.nodeOwnerDocument(child);
+        const self_owner = parser.nodeOwnerDocument(self);
+        const child_owner = parser.nodeOwnerDocument(child);
 
         // If the node to be inserted has a different ownerDocument than the parent node,
         // modern browsers automatically adopt the node and its descendants into
@@ -272,14 +272,14 @@ pub const Node = struct {
             return 0;
         }
 
-        const docself = try parser.nodeOwnerDocument(self) orelse blk: {
-            if (try parser.nodeType(self) == .document) {
+        const docself = parser.nodeOwnerDocument(self) orelse blk: {
+            if (parser.nodeType(self) == .document) {
                 break :blk @as(*parser.Document, @ptrCast(self));
             }
             break :blk null;
         };
-        const docother = try parser.nodeOwnerDocument(other) orelse blk: {
-            if (try parser.nodeType(other) == .document) {
+        const docother = parser.nodeOwnerDocument(other) orelse blk: {
+            if (parser.nodeType(other) == .document) {
                 break :blk @as(*parser.Document, @ptrCast(other));
             }
             break :blk null;
@@ -299,8 +299,8 @@ pub const Node = struct {
                 @intFromEnum(parser.DocumentPosition.contained_by);
         }
 
-        const rootself = try parser.nodeGetRootNode(self);
-        const rootother = try parser.nodeGetRootNode(other);
+        const rootself = parser.nodeGetRootNode(self);
+        const rootother = parser.nodeGetRootNode(other);
         if (rootself != rootother) {
             return @intFromEnum(parser.DocumentPosition.disconnected) +
                 @intFromEnum(parser.DocumentPosition.implementation_specific) +
@@ -347,8 +347,8 @@ pub const Node = struct {
         return 0;
     }
 
-    pub fn _contains(self: *parser.Node, other: *parser.Node) !bool {
-        return try parser.nodeContains(self, other);
+    pub fn _contains(self: *parser.Node, other: *parser.Node) bool {
+        return parser.nodeContains(self, other);
     }
 
     // Returns itself or ancestor object inheriting from Node.
@@ -360,32 +360,44 @@ pub const Node = struct {
         node: Union,
     };
     pub fn _getRootNode(self: *parser.Node, options: ?struct { composed: bool = false }, page: *Page) !GetRootNodeResult {
-        if (options) |options_| if (options_.composed) {
-            log.warn(.web_api, "not implemented", .{ .feature = "getRootNode composed" });
-        };
+        const composed = if (options) |opts| opts.composed else false;
 
-        const root = try parser.nodeGetRootNode(self);
-        if (page.getNodeState(root)) |state| {
-            if (state.shadow_root) |sr| {
-                return .{ .shadow_root = sr };
+        var current_root = parser.nodeGetRootNode(self);
+
+        while (true) {
+            const node_type = parser.nodeType(current_root);
+
+            if (node_type == .document_fragment) {
+                if (parser.documentFragmentGetHost(@ptrCast(current_root))) |host| {
+                    if (page.getNodeState(host)) |state| {
+                        if (state.shadow_root) |sr| {
+                            if (!composed) {
+                                return .{ .shadow_root = sr };
+                            }
+                            current_root = parser.nodeGetRootNode(@ptrCast(sr.host));
+                            continue;
+                        }
+                    }
+                }
             }
+            break;
         }
 
-        return .{ .node = try Node.toInterface(root) };
+        return .{ .node = try Node.toInterface(current_root) };
     }
 
-    pub fn _hasChildNodes(self: *parser.Node) !bool {
-        return try parser.nodeHasChildNodes(self);
+    pub fn _hasChildNodes(self: *parser.Node) bool {
+        return parser.nodeHasChildNodes(self);
     }
 
     pub fn get_childNodes(self: *parser.Node, page: *Page) !NodeList {
         const allocator = page.arena;
         var list: NodeList = .{};
 
-        var n = try parser.nodeFirstChild(self) orelse return list;
+        var n = parser.nodeFirstChild(self) orelse return list;
         while (true) {
             try list.append(allocator, n);
-            n = try parser.nodeNextSibling(n) orelse return list;
+            n = parser.nodeNextSibling(n) orelse return list;
         }
     }
 
@@ -394,8 +406,8 @@ pub const Node = struct {
             return _appendChild(self, new_node);
         }
 
-        const self_owner = try parser.nodeOwnerDocument(self);
-        const new_node_owner = try parser.nodeOwnerDocument(new_node);
+        const self_owner = parser.nodeOwnerDocument(self);
+        const new_node_owner = parser.nodeOwnerDocument(new_node);
 
         // If the node to be inserted has a different ownerDocument than the parent node,
         // modern browsers automatically adopt the node and its descendants into
@@ -415,7 +427,7 @@ pub const Node = struct {
     }
 
     pub fn _isDefaultNamespace(self: *parser.Node, namespace: ?[]const u8) !bool {
-        return try parser.nodeIsDefaultNamespace(self, namespace);
+        return parser.nodeIsDefaultNamespace(self, namespace);
     }
 
     pub fn _isEqualNode(self: *parser.Node, other: *parser.Node) !bool {
@@ -423,10 +435,10 @@ pub const Node = struct {
         return try parser.nodeIsEqualNode(self, other);
     }
 
-    pub fn _isSameNode(self: *parser.Node, other: *parser.Node) !bool {
+    pub fn _isSameNode(self: *parser.Node, other: *parser.Node) bool {
         // TODO: other is not an optional parameter, but can be null.
         // NOTE: there is no need to use isSameNode(); instead use the === strict equality operator
-        return try parser.nodeIsSameNode(self, other);
+        return parser.nodeIsSameNode(self, other);
     }
 
     pub fn _lookupPrefix(self: *parser.Node, namespace: ?[]const u8) !?[]const u8 {
@@ -461,7 +473,7 @@ pub const Node = struct {
 
     // Check if the hierarchy node tree constraints are respected.
     // For now, it checks only if new nodes are not self.
-    // TODO implements the others contraints.
+    // TODO implements the others constraints.
     // see https://dom.spec.whatwg.org/#concept-node-tree
     pub fn hierarchy(self: *parser.Node, nodes: []const NodeOrText) bool {
         for (nodes) |n| {
@@ -482,9 +494,9 @@ pub const Node = struct {
             return parser.DOMError.HierarchyRequest;
         }
 
-        const doc = (try parser.nodeOwnerDocument(self)) orelse return;
+        const doc = (parser.nodeOwnerDocument(self)) orelse return;
 
-        if (try parser.nodeFirstChild(self)) |first| {
+        if (parser.nodeFirstChild(self)) |first| {
             for (nodes) |node| {
                 _ = try parser.nodeInsertBefore(self, try node.toNode(doc), first);
             }
@@ -506,7 +518,7 @@ pub const Node = struct {
             return parser.DOMError.HierarchyRequest;
         }
 
-        const doc = (try parser.nodeOwnerDocument(self)) orelse return;
+        const doc = (parser.nodeOwnerDocument(self)) orelse return;
         for (nodes) |node| {
             _ = try parser.nodeAppendChild(self, try node.toNode(doc));
         }
@@ -525,7 +537,7 @@ pub const Node = struct {
         // remove existing children
         try removeChildren(self);
 
-        const doc = (try parser.nodeOwnerDocument(self)) orelse return;
+        const doc = (parser.nodeOwnerDocument(self)) orelse return;
         // add new children
         for (nodes) |node| {
             _ = try parser.nodeAppendChild(self, try node.toNode(doc));
@@ -533,30 +545,30 @@ pub const Node = struct {
     }
 
     pub fn removeChildren(self: *parser.Node) !void {
-        if (!try parser.nodeHasChildNodes(self)) return;
+        if (!parser.nodeHasChildNodes(self)) return;
 
         const children = try parser.nodeGetChildNodes(self);
-        const ln = try parser.nodeListLength(children);
+        const ln = parser.nodeListLength(children);
         var i: u32 = 0;
         while (i < ln) {
             defer i += 1;
             // we always retrieve the 0 index child on purpose: libdom nodelist
             // are dynamic. So the next child to remove is always as pos 0.
-            const child = try parser.nodeListItem(children, 0) orelse continue;
+            const child = parser.nodeListItem(children, 0) orelse continue;
             _ = try parser.nodeRemoveChild(self, child);
         }
     }
 
     pub fn before(self: *parser.Node, nodes: []const NodeOrText) !void {
-        const parent = try parser.nodeParentNode(self) orelse return;
-        const doc = (try parser.nodeOwnerDocument(parent)) orelse return;
+        const parent = parser.nodeParentNode(self) orelse return;
+        const doc = (parser.nodeOwnerDocument(parent)) orelse return;
 
         var sibling: ?*parser.Node = self;
         // have to find the first sibling that isn't in nodes
         CHECK: while (sibling) |s| {
             for (nodes) |n| {
                 if (n.is(s)) {
-                    sibling = try parser.nodePreviousSibling(s);
+                    sibling = parser.nodePreviousSibling(s);
                     continue :CHECK;
                 }
             }
@@ -564,7 +576,7 @@ pub const Node = struct {
         }
 
         if (sibling == null) {
-            sibling = try parser.nodeFirstChild(parent);
+            sibling = parser.nodeFirstChild(parent);
         }
 
         if (sibling) |ref_node| {
@@ -578,15 +590,15 @@ pub const Node = struct {
     }
 
     pub fn after(self: *parser.Node, nodes: []const NodeOrText) !void {
-        const parent = try parser.nodeParentNode(self) orelse return;
-        const doc = (try parser.nodeOwnerDocument(parent)) orelse return;
+        const parent = parser.nodeParentNode(self) orelse return;
+        const doc = (parser.nodeOwnerDocument(parent)) orelse return;
 
         // have to find the first sibling that isn't in nodes
-        var sibling = try parser.nodeNextSibling(self);
+        var sibling = parser.nodeNextSibling(self);
         CHECK: while (sibling) |s| {
             for (nodes) |n| {
                 if (n.is(s)) {
-                    sibling = try parser.nodeNextSibling(s);
+                    sibling = parser.nodeNextSibling(s);
                     continue :CHECK;
                 }
             }

src/browser/dom/node_filter.zig

@@ -17,8 +17,8 @@
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 const std = @import("std");
+const js = @import("../js/js.zig");
 const parser = @import("../netsurf.zig");
-const Env = @import("../env.zig").Env;
 const Node = @import("node.zig").Node;
 
 pub const NodeFilter = struct {
@@ -43,10 +43,13 @@ pub const NodeFilter = struct {
 
 const VerifyResult = enum { accept, skip, reject };
 
-pub fn verify(what_to_show: u32, filter: ?Env.Function, node: *parser.Node) !VerifyResult {
-    const node_type = try parser.nodeType(node);
+pub fn verify(what_to_show: u32, filter: ?js.Function, node: *parser.Node) !VerifyResult {
+    const node_type = parser.nodeType(node);
 
     // Verify that we can show this node type.
+    // Per the DOM spec, what_to_show filters which nodes to return, but should
+    // still traverse children. So we return .skip (not .reject) when the node
+    // type doesn't match.
     if (!switch (node_type) {
         .attribute => what_to_show & NodeFilter._SHOW_ATTRIBUTE != 0,
         .cdata_section => what_to_show & NodeFilter._SHOW_CDATA_SECTION != 0,
@@ -60,7 +63,7 @@ pub fn verify(what_to_show: u32, filter: ?Env.Function, node: *parser.Node) !Ver
         .notation => what_to_show & NodeFilter._SHOW_NOTATION != 0,
         .processing_instruction => what_to_show & NodeFilter._SHOW_PROCESSING_INSTRUCTION != 0,
         .text => what_to_show & NodeFilter._SHOW_TEXT != 0,
-    }) return .reject;
+    }) return .skip;
 
     // Verify that we aren't filtering it out.
     if (filter) |f| {

src/browser/dom/node_iterator.zig

@@ -18,8 +18,8 @@
 
 const std = @import("std");
 
+const js = @import("../js/js.zig");
 const parser = @import("../netsurf.zig");
-const Env = @import("../env.zig").Env;
 const NodeFilter = @import("node_filter.zig");
 const Node = @import("node.zig").Node;
 const NodeUnion = @import("node.zig").Union;
@@ -37,7 +37,7 @@ pub const NodeIterator = struct {
     reference_node: *parser.Node,
     what_to_show: u32,
     filter: ?NodeIteratorOpts,
-    filter_func: ?Env.Function,
+    filter_func: ?js.Function,
     pointer_before_current: bool = true,
     // used to track / block recursive filters
     is_in_callback: bool = false,
@@ -45,15 +45,15 @@ pub const NodeIterator = struct {
     // One of the few cases where null and undefined resolve to different default.
     // We need the raw JsObject so that we can probe the tri state:
     // null, undefined or i32.
-    pub const WhatToShow = Env.JsObject;
+    pub const WhatToShow = js.Object;
 
     pub const NodeIteratorOpts = union(enum) {
-        function: Env.Function,
-        object: struct { acceptNode: Env.Function },
+        function: js.Function,
+        object: struct { acceptNode: js.Function },
     };
 
     pub fn init(node: *parser.Node, what_to_show_: ?WhatToShow, filter: ?NodeIteratorOpts) !NodeIterator {
-        var filter_func: ?Env.Function = null;
+        var filter_func: ?js.Function = null;
         if (filter) |f| {
             filter_func = switch (f) {
                 .function => |func| func,
@@ -74,10 +74,10 @@ pub const NodeIterator = struct {
 
         return .{
             .root = node,
-            .reference_node = node,
-            .what_to_show = what_to_show,
             .filter = filter,
+            .reference_node = node,
             .filter_func = filter_func,
+            .what_to_show = what_to_show,
         };
     }
 
@@ -115,17 +115,30 @@ pub const NodeIterator = struct {
 
         if (try self.firstChild(self.reference_node)) |child| {
             self.reference_node = child;
+            self.pointer_before_current = false;
             return try Node.toInterface(child);
         }
 
         var current = self.reference_node;
         while (current != self.root) {
-            if (try self.nextSibling(current)) |sibling| {
-                self.reference_node = sibling;
-                return try Node.toInterface(sibling);
+            // Try to get next sibling (including .skip/.reject nodes we need to descend into)
+            if (try self.nextSiblingOrSkipReject(current)) |result| {
+                if (result.should_descend) {
+                    // This is a .skip/.reject node - try to find acceptable children within it
+                    if (try self.firstChild(result.node)) |child| {
+                        self.reference_node = child;
+                        return try Node.toInterface(child);
+                    }
+                    // No acceptable children, continue looking at this node's siblings
+                    current = result.node;
+                    continue;
+                }
+                // This is an .accept node - return it
+                self.reference_node = result.node;
+                return try Node.toInterface(result.node);
             }
 
-            current = (try parser.nodeParentNode(current)) orelse break;
+            current = (parser.nodeParentNode(current)) orelse break;
         }
 
         return null;
@@ -147,7 +160,7 @@ pub const NodeIterator = struct {
         }
 
         var current = self.reference_node;
-        while (try parser.nodePreviousSibling(current)) |previous| {
+        while (parser.nodePreviousSibling(current)) |previous| {
             current = previous;
 
             switch (try NodeFilter.verify(self.what_to_show, self.filter_func, current)) {
@@ -189,11 +202,11 @@ pub const NodeIterator = struct {
 
     fn firstChild(self: *const NodeIterator, node: *parser.Node) !?*parser.Node {
         const children = try parser.nodeGetChildNodes(node);
-        const child_count = try parser.nodeListLength(children);
+        const child_count = parser.nodeListLength(children);
 
         for (0..child_count) |i| {
             const index: u32 = @intCast(i);
-            const child = (try parser.nodeListItem(children, index)) orelse return null;
+            const child = (parser.nodeListItem(children, index)) orelse return null;
 
             switch (try NodeFilter.verify(self.what_to_show, self.filter_func, child)) {
                 .accept => return child, // NOTE: Skip and reject are equivalent for NodeIterator, this is different from TreeWalker
@@ -206,12 +219,12 @@ pub const NodeIterator = struct {
 
     fn lastChild(self: *const NodeIterator, node: *parser.Node) !?*parser.Node {
         const children = try parser.nodeGetChildNodes(node);
-        const child_count = try parser.nodeListLength(children);
+        const child_count = parser.nodeListLength(children);
 
         var index: u32 = child_count;
         while (index > 0) {
             index -= 1;
-            const child = (try parser.nodeListItem(children, index)) orelse return null;
+            const child = (parser.nodeListItem(children, index)) orelse return null;
 
             switch (try NodeFilter.verify(self.what_to_show, self.filter_func, child)) {
                 .accept => return child, // NOTE: Skip and reject are equivalent for NodeIterator, this is different from TreeWalker
@@ -229,7 +242,7 @@ pub const NodeIterator = struct {
         var current = node;
         while (true) {
             if (current == self.root) return null;
-            current = (try parser.nodeParentNode(current)) orelse return null;
+            current = (parser.nodeParentNode(current)) orelse return null;
 
             switch (try NodeFilter.verify(self.what_to_show, self.filter_func, current)) {
                 .accept => return current,
@@ -243,7 +256,7 @@ pub const NodeIterator = struct {
         var current = node;
 
         while (true) {
-            current = (try parser.nodeNextSibling(current)) orelse return null;
+            current = (parser.nodeNextSibling(current)) orelse return null;
 
             switch (try NodeFilter.verify(self.what_to_show, self.filter_func, current)) {
                 .accept => return current,
@@ -254,6 +267,22 @@ pub const NodeIterator = struct {
         return null;
     }
 
+    // Get the next sibling that is either acceptable or should be descended into (skip/reject)
+    fn nextSiblingOrSkipReject(self: *const NodeIterator, node: *parser.Node) !?struct { node: *parser.Node, should_descend: bool } {
+        var current = node;
+
+        while (true) {
+            current = (parser.nodeNextSibling(current)) orelse return null;
+
+            switch (try NodeFilter.verify(self.what_to_show, self.filter_func, current)) {
+                .accept => return .{ .node = current, .should_descend = false },
+                .skip, .reject => return .{ .node = current, .should_descend = true },
+            }
+        }
+
+        return null;
+    }
+
     fn callbackStart(self: *NodeIterator) !void {
         if (self.is_in_callback) {
             // this is the correct DOMExeption

src/browser/dom/nodelist.zig

@@ -17,13 +17,12 @@
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 const std = @import("std");
+const Allocator = std.mem.Allocator;
 
+const js = @import("../js/js.zig");
 const log = @import("../../log.zig");
 const parser = @import("../netsurf.zig");
 
-const JsThis = @import("../env.zig").JsThis;
-const Function = @import("../env.zig").Function;
-
 const NodeUnion = @import("node.zig").Union;
 const Node = @import("node.zig").Node;
 
@@ -101,13 +100,20 @@ pub const NodeList = struct {
 
     nodes: NodesArrayList = .{},
 
-    pub fn deinit(self: *NodeList, alloc: std.mem.Allocator) void {
-        // TODO unref all nodes
-        self.nodes.deinit(alloc);
+    pub fn deinit(self: *NodeList, allocator: Allocator) void {
+        self.nodes.deinit(allocator);
     }
 
-    pub fn append(self: *NodeList, alloc: std.mem.Allocator, node: *parser.Node) !void {
-        try self.nodes.append(alloc, node);
+    pub fn ensureTotalCapacity(self: *NodeList, allocator: Allocator, n: usize) !void {
+        return self.nodes.ensureTotalCapacity(allocator, n);
+    }
+
+    pub fn append(self: *NodeList, allocator: Allocator, node: *parser.Node) !void {
+        try self.nodes.append(allocator, node);
+    }
+
+    pub fn appendAssumeCapacity(self: *NodeList, node: *parser.Node) void {
+        self.nodes.appendAssumeCapacity(node);
     }
 
     pub fn get_length(self: *const NodeList) u32 {
@@ -140,10 +146,10 @@ pub const NodeList = struct {
     //     };
     // }
 
-    pub fn _forEach(self: *NodeList, cbk: Function) !void { // TODO handle thisArg
+    pub fn _forEach(self: *NodeList, cbk: js.Function) !void { // TODO handle thisArg
         for (self.nodes.items, 0..) |n, i| {
             const ii: u32 = @intCast(i);
-            var result: Function.Result = undefined;
+            var result: js.Function.Result = undefined;
             cbk.tryCall(void, .{ n, ii, self }, &result) catch {
                 log.debug(.user_script, "forEach callback", .{ .err = result.exception, .stack = result.stack });
             };
@@ -167,7 +173,7 @@ pub const NodeList = struct {
     }
 
     // TODO entries() https://developer.mozilla.org/en-US/docs/Web/API/NodeList/entries
-    pub fn postAttach(self: *NodeList, js_this: JsThis) !void {
+    pub fn postAttach(self: *NodeList, js_this: js.This) !void {
         const len = self.get_length();
         for (0..len) |i| {
             const node = try self._item(@intCast(i)) orelse unreachable;

src/browser/dom/performance.zig

@@ -18,9 +18,9 @@
 
 const std = @import("std");
 
+const js = @import("../js/js.zig");
 const parser = @import("../netsurf.zig");
 const EventTarget = @import("../dom/event_target.zig").EventTarget;
-const Env = @import("../env.zig").Env;
 const Page = @import("../page.zig").Page;
 
 const milliTimestamp = @import("../../datetime.zig").milliTimestamp;
@@ -61,7 +61,7 @@ pub const Performance = struct {
         return milliTimestamp() - self.time_origin;
     }
 
-    pub fn _mark(_: *Performance, name: []const u8, _options: ?PerformanceMark.Options, page: *Page) !PerformanceMark {
+    pub fn _mark(_: *Performance, name: js.String, _options: ?PerformanceMark.Options, page: *Page) !PerformanceMark {
         const mark: PerformanceMark = try .constructor(name, _options, page);
         // TODO: Should store this in an entries list
         return mark;
@@ -148,14 +148,14 @@ pub const PerformanceMark = struct {
     pub const prototype = *PerformanceEntry;
 
     proto: PerformanceEntry,
-    detail: ?Env.JsObject,
+    detail: ?js.Object,
 
     const Options = struct {
-        detail: ?Env.JsObject = null,
+        detail: ?js.Object = null,
         startTime: ?f64 = null,
     };
 
-    pub fn constructor(name: []const u8, _options: ?Options, page: *Page) !PerformanceMark {
+    pub fn constructor(name: js.String, _options: ?Options, page: *Page) !PerformanceMark {
         const perf = &page.window.performance;
 
         const options = _options orelse Options{};
@@ -166,14 +166,12 @@ pub const PerformanceMark = struct {
         }
 
         const detail = if (options.detail) |d| try d.persist() else null;
-
-        const duped_name = try page.arena.dupe(u8, name);
-        const proto = PerformanceEntry{ .name = duped_name, .entry_type = .mark, .start_time = start_time };
+        const proto = PerformanceEntry{ .name = name.string, .entry_type = .mark, .start_time = start_time };
 
         return .{ .proto = proto, .detail = detail };
     }
 
-    pub fn get_detail(self: *const PerformanceMark) ?Env.JsObject {
+    pub fn get_detail(self: *const PerformanceMark) ?js.Object {
         return self.detail;
     }
 };
@@ -197,7 +195,7 @@ test "Performance: now" {
     }
 
     var after = perf._now();
-    while (after <= now) { // Loop untill after > now
+    while (after <= now) { // Loop until after > now
         try testing.expectEqual(after, now);
         after = perf._now();
     }

src/browser/dom/performance_observer.zig

@@ -17,7 +17,7 @@
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 const std = @import("std");
-const Env = @import("../env.zig").Env;
+const js = @import("../js/js.zig");
 
 const PerformanceEntry = @import("performance.zig").PerformanceEntry;
 
@@ -25,7 +25,7 @@ const PerformanceEntry = @import("performance.zig").PerformanceEntry;
 pub const PerformanceObserver = struct {
     pub const _supportedEntryTypes = [0][]const u8{};
 
-    pub fn constructor(cbk: Env.Function) PerformanceObserver {
+    pub fn constructor(cbk: js.Function) PerformanceObserver {
         _ = cbk;
         return .{};
     }

src/browser/dom/processing_instruction.zig

@@ -48,7 +48,7 @@ pub const ProcessingInstruction = struct {
     }
 
     pub fn get_data(self: *parser.ProcessingInstruction) !?[]const u8 {
-        return try parser.nodeValue(parser.processingInstructionToNode(self));
+        return parser.nodeValue(parser.processingInstructionToNode(self));
     }
 
     pub fn set_data(self: *parser.ProcessingInstruction, data: []u8) !void {
@@ -58,7 +58,7 @@ pub const ProcessingInstruction = struct {
     // netsurf's ProcessInstruction doesn't implement the dom_node_get_attributes
     // and thus will crash if we try to call nodeIsEqualNode.
     pub fn _isEqualNode(self: *parser.ProcessingInstruction, other_node: *parser.Node) !bool {
-        if (try parser.nodeType(other_node) != .processing_instruction) {
+        if (parser.nodeType(other_node) != .processing_instruction) {
             return false;
         }
 

src/browser/dom/range.zig

@@ -92,7 +92,7 @@ pub const Range = struct {
     pub fn _setStart(self: *Range, node: *parser.Node, offset_: i32) !void {
         try ensureValidOffset(node, offset_);
         const offset: u32 = @intCast(offset_);
-        const position = compare(node, offset, self.proto.start_node, self.proto.start_offset) catch |err| switch (err) {
+        const position = compare(node, offset, self.proto.end_node, self.proto.end_offset) catch |err| switch (err) {
             error.WrongDocument => blk: {
                 // allow a node with a different root than the current, or
                 // a disconnected one. Treat it as if it's "after", so that
@@ -103,7 +103,7 @@ pub const Range = struct {
         };
 
         if (position == 1) {
-            // if we're setting the node after the current start, the end must
+            // if we're setting the node after the current end, the end must
             // be set too.
             self.proto.end_offset = offset;
             self.proto.end_node = node;
@@ -176,10 +176,10 @@ pub const Range = struct {
         self.proto.end_node = node;
 
         // Set end_offset
-        switch (try parser.nodeType(node)) {
+        switch (parser.nodeType(node)) {
             .text, .cdata_section, .comment, .processing_instruction => {
                 // For text-like nodes, end_offset should be the length of the text data
-                if (try parser.nodeValue(node)) |text_data| {
+                if (parser.nodeValue(node)) |text_data| {
                     self.proto.end_offset = @intCast(text_data.len);
                 } else {
                     self.proto.end_offset = 0;
@@ -188,7 +188,7 @@ pub const Range = struct {
             else => {
                 // For element and other nodes, end_offset is the number of children
                 const child_nodes = try parser.nodeGetChildNodes(node);
-                const child_count = try parser.nodeListLength(child_nodes);
+                const child_count = parser.nodeListLength(child_nodes);
                 self.proto.end_offset = @intCast(child_count);
             },
         }
@@ -211,7 +211,7 @@ pub const Range = struct {
 
     pub fn _comparePoint(self: *const Range, node: *parser.Node, offset_: i32) !i32 {
         const start = self.proto.start_node;
-        if (try parser.nodeGetRootNode(start) != try parser.nodeGetRootNode(node)) {
+        if (parser.nodeGetRootNode(start) != parser.nodeGetRootNode(node)) {
             // WPT really wants this error to be first. Later, when we check
             // if the relative position is 'disconnected', it'll also catch this
             // case, but WPT will complain because it sometimes also sends
@@ -219,7 +219,7 @@ pub const Range = struct {
             return error.WrongDocument;
         }
 
-        if (try parser.nodeType(node) == .document_type) {
+        if (parser.nodeType(node) == .document_type) {
             return error.InvalidNodeType;
         }
 
@@ -245,8 +245,8 @@ pub const Range = struct {
     }
 
     pub fn _intersectsNode(self: *const Range, node: *parser.Node) !bool {
-        const start_root = try parser.nodeGetRootNode(self.proto.start_node);
-        const node_root = try parser.nodeGetRootNode(node);
+        const start_root = parser.nodeGetRootNode(self.proto.start_node);
+        const node_root = parser.nodeGetRootNode(node);
         if (start_root != node_root) {
             return false;
         }
@@ -299,29 +299,29 @@ fn ensureValidOffset(node: *parser.Node, offset: i32) !void {
 
 fn nodeLength(node: *parser.Node) !usize {
     switch (try isTextual(node)) {
-        true => return ((try parser.nodeTextContent(node)) orelse "").len,
+        true => return ((parser.nodeTextContent(node)) orelse "").len,
         false => {
             const children = try parser.nodeGetChildNodes(node);
-            return @intCast(try parser.nodeListLength(children));
+            return @intCast(parser.nodeListLength(children));
         },
     }
 }
 
 fn isTextual(node: *parser.Node) !bool {
-    return switch (try parser.nodeType(node)) {
+    return switch (parser.nodeType(node)) {
         .text, .comment, .cdata_section => true,
         else => false,
     };
 }
 
 fn getParentAndIndex(child: *parser.Node) !struct { *parser.Node, u32 } {
-    const parent = (try parser.nodeParentNode(child)) orelse return error.InvalidNodeType;
+    const parent = (parser.nodeParentNode(child)) orelse return error.InvalidNodeType;
     const children = try parser.nodeGetChildNodes(parent);
-    const ln = try parser.nodeListLength(children);
+    const ln = parser.nodeListLength(children);
     var i: u32 = 0;
     while (i < ln) {
         defer i += 1;
-        const c = try parser.nodeListItem(children, i) orelse continue;
+        const c = parser.nodeListItem(children, i) orelse continue;
         if (c == child) {
             return .{ parent, i };
         }
@@ -363,7 +363,7 @@ fn compare(node_a: *parser.Node, offset_a: u32, node_b: *parser.Node, offset_b:
     if (position & @intFromEnum(parser.DocumentPosition.contains) == @intFromEnum(parser.DocumentPosition.contains)) {
         // node_a contains node_b
         var child = node_b;
-        while (try parser.nodeParentNode(child)) |parent| {
+        while (parser.nodeParentNode(child)) |parent| {
             if (parent == node_a) {
                 // child.parentNode == node_a
                 break;
@@ -378,7 +378,7 @@ fn compare(node_a: *parser.Node, offset_a: u32, node_b: *parser.Node, offset_b:
 
         const child_parent, const child_index = try getParentAndIndex(child);
         std.debug.assert(node_a == child_parent);
-        return if (child_index < offset_a) -1 else 1;
+        return if (offset_a <= child_index) -1 else 1;
     }
 
     return -1;

src/browser/dom/resize_observer.zig

@@ -16,7 +16,7 @@
 // You should have received a copy of the GNU Affero General Public License
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
-const Env = @import("../env.zig").Env;
+const js = @import("../js/js.zig");
 const parser = @import("../netsurf.zig");
 
 pub const Interfaces = .{
@@ -25,7 +25,7 @@ pub const Interfaces = .{
 
 // WEB IDL https://drafts.csswg.org/resize-observer/#resize-observer-interface
 pub const ResizeObserver = struct {
-    pub fn constructor(cbk: Env.Function) ResizeObserver {
+    pub fn constructor(cbk: js.Function) ResizeObserver {
         _ = cbk;
         return .{};
     }

src/browser/dom/shadow_root.zig

@@ -20,7 +20,7 @@ const std = @import("std");
 const dump = @import("../dump.zig");
 const parser = @import("../netsurf.zig");
 
-const Env = @import("../env.zig").Env;
+const js = @import(".././js/js.zig");
 const Page = @import("../page.zig").Page;
 const Node = @import("node.zig").Node;
 const Element = @import("element.zig").Element;
@@ -34,7 +34,7 @@ pub const ShadowRoot = struct {
     mode: Mode,
     host: *parser.Element,
     proto: *parser.DocumentFragment,
-    adopted_style_sheets: ?Env.JsObject = null,
+    adopted_style_sheets: ?js.Object = null,
 
     pub const Mode = enum {
         open,
@@ -45,17 +45,17 @@ pub const ShadowRoot = struct {
         return Element.toInterface(self.host);
     }
 
-    pub fn get_adoptedStyleSheets(self: *ShadowRoot, page: *Page) !Env.JsObject {
+    pub fn get_adoptedStyleSheets(self: *ShadowRoot, page: *Page) !js.Object {
         if (self.adopted_style_sheets) |obj| {
             return obj;
         }
 
-        const obj = try page.main_context.newArray(0).persist();
+        const obj = try page.js.createArray(0).persist();
         self.adopted_style_sheets = obj;
         return obj;
     }
 
-    pub fn set_adoptedStyleSheets(self: *ShadowRoot, sheets: Env.JsObject) !void {
+    pub fn set_adoptedStyleSheets(self: *ShadowRoot, sheets: js.Object) !void {
         self.adopted_style_sheets = try sheets.persist();
     }
 
@@ -67,7 +67,7 @@ pub const ShadowRoot = struct {
 
     pub fn set_innerHTML(self: *ShadowRoot, str_: ?[]const u8) !void {
         const sr_doc = parser.documentFragmentToNode(self.proto);
-        const doc = try parser.nodeOwnerDocument(sr_doc) orelse return parser.DOMError.WrongDocument;
+        const doc = parser.nodeOwnerDocument(sr_doc) orelse return parser.DOMError.WrongDocument;
         try Node.removeChildren(sr_doc);
         const str = str_ orelse return;
 
@@ -80,16 +80,16 @@ pub const ShadowRoot = struct {
         // element.
         // For ShadowRoot, it appears the only the children within the body should
         // be set.
-        const html = try parser.nodeFirstChild(fragment_node) orelse return;
-        const head = try parser.nodeFirstChild(html) orelse return;
-        const body = try parser.nodeNextSibling(head) orelse return;
+        const html = parser.nodeFirstChild(fragment_node) orelse return;
+        const head = parser.nodeFirstChild(html) orelse return;
+        const body = parser.nodeNextSibling(head) orelse return;
 
         const children = try parser.nodeGetChildNodes(body);
-        const ln = try parser.nodeListLength(children);
+        const ln = parser.nodeListLength(children);
         for (0..ln) |_| {
             // always index 0, because nodeAppendChild moves the node out of
             // the nodeList and into the new tree
-            const child = try parser.nodeListItem(children, 0) orelse continue;
+            const child = parser.nodeListItem(children, 0) orelse continue;
             _ = try parser.nodeAppendChild(sr_doc, child);
         }
     }

src/browser/dom/token_list.zig

@@ -18,12 +18,11 @@
 
 const std = @import("std");
 
+const js = @import("../js/js.zig");
 const log = @import("../../log.zig");
 const parser = @import("../netsurf.zig");
 const iterator = @import("../iterator/iterator.zig");
 
-const Function = @import("../env.zig").Function;
-const JsObject = @import("../env.zig").JsObject;
 const DOMException = @import("exceptions.zig").DOMException;
 
 pub const Interfaces = .{
@@ -137,10 +136,10 @@ pub const DOMTokenList = struct {
     }
 
     // TODO handle thisArg
-    pub fn _forEach(self: *parser.TokenList, cbk: Function, this_arg: JsObject) !void {
+    pub fn _forEach(self: *parser.TokenList, cbk: js.Function, this_arg: js.Object) !void {
         var entries = _entries(self);
         while (try entries._next()) |entry| {
-            var result: Function.Result = undefined;
+            var result: js.Function.Result = undefined;
             cbk.tryCallWithThis(void, this_arg, .{ entry.@"1", entry.@"0", self }, &result) catch {
                 log.debug(.user_script, "callback error", .{
                     .err = result.exception,

src/browser/dom/tree_walker.zig

@@ -17,11 +17,10 @@
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 const std = @import("std");
+const js = @import("../js/js.zig");
 const parser = @import("../netsurf.zig");
 
 const NodeFilter = @import("node_filter.zig");
-const Env = @import("../env.zig").Env;
-const Page = @import("../page.zig").Page;
 const Node = @import("node.zig").Node;
 const NodeUnion = @import("node.zig").Union;
 
@@ -31,20 +30,20 @@ pub const TreeWalker = struct {
     current_node: *parser.Node,
     what_to_show: u32,
     filter: ?TreeWalkerOpts,
-    filter_func: ?Env.Function,
+    filter_func: ?js.Function,
 
     // One of the few cases where null and undefined resolve to different default.
     // We need the raw JsObject so that we can probe the tri state:
     // null, undefined or i32.
-    pub const WhatToShow = Env.JsObject;
+    pub const WhatToShow = js.Object;
 
     pub const TreeWalkerOpts = union(enum) {
-        function: Env.Function,
-        object: struct { acceptNode: Env.Function },
+        function: js.Function,
+        object: struct { acceptNode: js.Function },
     };
 
     pub fn init(node: *parser.Node, what_to_show_: ?WhatToShow, filter: ?TreeWalkerOpts) !TreeWalker {
-        var filter_func: ?Env.Function = null;
+        var filter_func: ?js.Function = null;
 
         if (filter) |f| {
             filter_func = switch (f) {
@@ -95,11 +94,11 @@ pub const TreeWalker = struct {
 
     fn firstChild(self: *const TreeWalker, node: *parser.Node) !?*parser.Node {
         const children = try parser.nodeGetChildNodes(node);
-        const child_count = try parser.nodeListLength(children);
+        const child_count = parser.nodeListLength(children);
 
         for (0..child_count) |i| {
             const index: u32 = @intCast(i);
-            const child = (try parser.nodeListItem(children, index)) orelse return null;
+            const child = (parser.nodeListItem(children, index)) orelse return null;
 
             switch (try NodeFilter.verify(self.what_to_show, self.filter_func, child)) {
                 .accept => return child,
@@ -113,12 +112,12 @@ pub const TreeWalker = struct {
 
     fn lastChild(self: *const TreeWalker, node: *parser.Node) !?*parser.Node {
         const children = try parser.nodeGetChildNodes(node);
-        const child_count = try parser.nodeListLength(children);
+        const child_count = parser.nodeListLength(children);
 
         var index: u32 = child_count;
         while (index > 0) {
             index -= 1;
-            const child = (try parser.nodeListItem(children, index)) orelse return null;
+            const child = (parser.nodeListItem(children, index)) orelse return null;
 
             switch (try NodeFilter.verify(self.what_to_show, self.filter_func, child)) {
                 .accept => return child,
@@ -134,7 +133,7 @@ pub const TreeWalker = struct {
         var current = node;
 
         while (true) {
-            current = (try parser.nodeNextSibling(current)) orelse return null;
+            current = (parser.nodeNextSibling(current)) orelse return null;
 
             switch (try NodeFilter.verify(self.what_to_show, self.filter_func, current)) {
                 .accept => return current,
@@ -145,11 +144,28 @@ pub const TreeWalker = struct {
         return null;
     }
 
+    // Get the next sibling that is either acceptable or should be descended into (skip)
+    fn nextSiblingOrSkip(self: *const TreeWalker, node: *parser.Node) !?struct { node: *parser.Node, should_descend: bool } {
+        var current = node;
+
+        while (true) {
+            current = (parser.nodeNextSibling(current)) orelse return null;
+
+            switch (try NodeFilter.verify(self.what_to_show, self.filter_func, current)) {
+                .accept => return .{ .node = current, .should_descend = false },
+                .skip => return .{ .node = current, .should_descend = true },
+                .reject => continue,
+            }
+        }
+
+        return null;
+    }
+
     fn previousSibling(self: *const TreeWalker, node: *parser.Node) !?*parser.Node {
         var current = node;
 
         while (true) {
-            current = (try parser.nodePreviousSibling(current)) orelse return null;
+            current = (parser.nodePreviousSibling(current)) orelse return null;
 
             switch (try NodeFilter.verify(self.what_to_show, self.filter_func, current)) {
                 .accept => return current,
@@ -166,7 +182,7 @@ pub const TreeWalker = struct {
         var current = node;
         while (true) {
             if (current == self.root) return null;
-            current = (try parser.nodeParentNode(current)) orelse return null;
+            current = (parser.nodeParentNode(current)) orelse return null;
 
             switch (try NodeFilter.verify(self.what_to_show, self.filter_func, current)) {
                 .accept => return current,
@@ -194,19 +210,36 @@ pub const TreeWalker = struct {
     }
 
     pub fn _nextNode(self: *TreeWalker) !?NodeUnion {
-        if (try self.firstChild(self.current_node)) |child| {
+        var current = self.current_node;
+
+        // First, try to go to first child of current node
+        if (try self.firstChild(current)) |child| {
             self.current_node = child;
             return try Node.toInterface(child);
         }
 
-        var current = self.current_node;
+        // No acceptable children, move to next node in tree
         while (current != self.root) {
-            if (try self.nextSibling(current)) |sibling| {
-                self.current_node = sibling;
-                return try Node.toInterface(sibling);
+            const result = try self.nextSiblingOrSkip(current) orelse {
+                // No next sibling, go up to parent and continue
+                // or, if there is no parent, we're done
+                current = (parser.nodeParentNode(current)) orelse break;
+                continue;
+            };
+
+            if (!result.should_descend) {
+                // This is an .accept node - return it
+                self.current_node = result.node;
+                return try Node.toInterface(result.node);
             }
 
-            current = (try parser.nodeParentNode(current)) orelse break;
+            // This is a .skip node - try to find acceptable children within it
+            if (try self.firstChild(result.node)) |child| {
+                self.current_node = child;
+                return try Node.toInterface(child);
+            }
+            // No acceptable children, continue looking at this node's siblings
+            current = result.node;
         }
 
         return null;
@@ -234,7 +267,7 @@ pub const TreeWalker = struct {
         if (self.current_node == self.root) return null;
 
         var current = self.current_node;
-        while (try parser.nodePreviousSibling(current)) |previous| {
+        while (parser.nodePreviousSibling(current)) |previous| {
             current = previous;
 
             switch (try NodeFilter.verify(self.what_to_show, self.filter_func, current)) {

src/browser/dom/walker.zig

@@ -44,39 +44,39 @@ pub const WalkerDepthFirst = struct {
         var n = cur orelse root;
 
         // TODO deinit next
-        if (try parser.nodeFirstChild(n)) |next| {
+        if (parser.nodeFirstChild(n)) |next| {
             return next;
         }
 
         // TODO deinit next
-        if (try parser.nodeNextSibling(n)) |next| {
+        if (parser.nodeNextSibling(n)) |next| {
             return next;
         }
 
         // TODO deinit parent
         // Back to the parent of cur.
         // If cur has no parent, then the iteration is over.
-        var parent = try parser.nodeParentNode(n) orelse return null;
+        var parent = parser.nodeParentNode(n) orelse return null;
 
         // TODO deinit lastchild
-        var lastchild = try parser.nodeLastChild(parent);
+        var lastchild = parser.nodeLastChild(parent);
         while (n != root and n == lastchild) {
             n = parent;
 
             // TODO deinit parent
             // Back to the prev's parent.
             // If prev has no parent, then the loop must stop.
-            parent = try parser.nodeParentNode(n) orelse break;
+            parent = parser.nodeParentNode(n) orelse break;
 
             // TODO deinit lastchild
-            lastchild = try parser.nodeLastChild(parent);
+            lastchild = parser.nodeLastChild(parent);
         }
 
         if (n == root) {
             return null;
         }
 
-        return try parser.nodeNextSibling(n);
+        return parser.nodeNextSibling(n);
     }
 };
 
@@ -84,14 +84,14 @@ pub const WalkerDepthFirst = struct {
 pub const WalkerChildren = struct {
     pub fn get_next(_: WalkerChildren, root: *parser.Node, cur: ?*parser.Node) !?*parser.Node {
         // On walk start, we return the first root's child.
-        if (cur == null) return try parser.nodeFirstChild(root);
+        if (cur == null) return parser.nodeFirstChild(root);
 
         // If cur is root, then return null.
         // This is a special case, if the root is included in the walk, we
         // don't want to go further to find children.
         if (root == cur.?) return null;
 
-        return try parser.nodeNextSibling(cur.?);
+        return parser.nodeNextSibling(cur.?);
     }
 };
 

src/browser/dump.zig

@@ -26,7 +26,13 @@ pub const Opts = struct {
     // set to include element shadowroots in the dump
     page: ?*const Page = null,
 
-    exclude_scripts: bool = false,
+    strip_mode: StripMode = .{},
+
+    pub const StripMode = struct {
+        js: bool = false,
+        ui: bool = false,
+        css: bool = false,
+    };
 };
 
 // writer must be a std.io.Writer
@@ -41,8 +47,8 @@ pub fn writeDocType(doc_type: *parser.DocumentType, writer: *std.Io.Writer) !voi
     try writer.writeAll("<!DOCTYPE ");
     try writer.writeAll(try parser.documentTypeGetName(doc_type));
 
-    const public_id = try parser.documentTypeGetPublicId(doc_type);
-    const system_id = try parser.documentTypeGetSystemId(doc_type);
+    const public_id = parser.documentTypeGetPublicId(doc_type);
+    const system_id = parser.documentTypeGetSystemId(doc_type);
     if (public_id.len != 0 and system_id.len != 0) {
         try writer.writeAll(" PUBLIC \"");
         try writeEscapedAttributeValue(writer, public_id);
@@ -63,11 +69,11 @@ pub fn writeDocType(doc_type: *parser.DocumentType, writer: *std.Io.Writer) !voi
 }
 
 pub fn writeNode(node: *parser.Node, opts: Opts, writer: *std.Io.Writer) anyerror!void {
-    switch (try parser.nodeType(node)) {
+    switch (parser.nodeType(node)) {
         .element => {
             // open the tag
             const tag_type = try parser.nodeHTMLGetTagType(node) orelse .undef;
-            if (opts.exclude_scripts and try isScriptOrRelated(tag_type, node)) {
+            if (try isStripped(tag_type, node, opts.strip_mode)) {
                 return;
             }
 
@@ -104,7 +110,7 @@ pub fn writeNode(node: *parser.Node, opts: Opts, writer: *std.Io.Writer) anyerro
             if (try isVoid(parser.nodeToElement(node))) return;
 
             if (tag_type == .script) {
-                try writer.writeAll(try parser.nodeTextContent(node) orelse "");
+                try writer.writeAll(parser.nodeTextContent(node) orelse "");
             } else {
                 // write the children
                 // TODO avoid recursion
@@ -117,17 +123,17 @@ pub fn writeNode(node: *parser.Node, opts: Opts, writer: *std.Io.Writer) anyerro
             try writer.writeAll(">");
         },
         .text => {
-            const v = try parser.nodeValue(node) orelse return;
+            const v = parser.nodeValue(node) orelse return;
             try writeEscapedTextNode(writer, v);
         },
         .cdata_section => {
-            const v = try parser.nodeValue(node) orelse return;
+            const v = parser.nodeValue(node) orelse return;
             try writer.writeAll("<![CDATA[");
             try writer.writeAll(v);
             try writer.writeAll("]]>");
         },
         .comment => {
-            const v = try parser.nodeValue(node) orelse return;
+            const v = parser.nodeValue(node) orelse return;
             try writer.writeAll("<!--");
             try writer.writeAll(v);
             try writer.writeAll("-->");
@@ -159,9 +165,22 @@ pub fn writeChildren(root: *parser.Node, opts: Opts, writer: *std.Io.Writer) !vo
     }
 }
 
-// When `exclude_scripts` is passed to dump, we don't include <script> tags.
-// We also want to omit <link rel=preload as=ascript>
-fn isScriptOrRelated(tag_type: parser.Tag, node: *parser.Node) !bool {
+fn isStripped(tag_type: parser.Tag, node: *parser.Node, strip_mode: Opts.StripMode) !bool {
+    if (strip_mode.js and try isJsRelated(tag_type, node)) {
+        return true;
+    }
+
+    if (strip_mode.css and try isCssRelated(tag_type, node)) {
+        return true;
+    }
+
+    if (strip_mode.ui and try isUIRelated(tag_type, node)) {
+        return true;
+    }
+    return false;
+}
+
+fn isJsRelated(tag_type: parser.Tag, node: *parser.Node) !bool {
     if (tag_type == .script) {
         return true;
     }
@@ -178,6 +197,34 @@ fn isScriptOrRelated(tag_type: parser.Tag, node: *parser.Node) !bool {
     return false;
 }
 
+fn isCssRelated(tag_type: parser.Tag, node: *parser.Node) !bool {
+    if (tag_type == .style) {
+        return true;
+    }
+    if (tag_type == .link) {
+        const el = parser.nodeToElement(node);
+        const rel = try parser.elementGetAttribute(el, "rel") orelse return false;
+        return std.ascii.eqlIgnoreCase(rel, "stylesheet");
+    }
+    return false;
+}
+
+fn isUIRelated(tag_type: parser.Tag, node: *parser.Node) !bool {
+    if (try isCssRelated(tag_type, node)) {
+        return true;
+    }
+    if (tag_type == .img or tag_type == .picture or tag_type == .video) {
+        return true;
+    }
+    if (tag_type == .undef) {
+        const name = try parser.nodeLocalName(node);
+        if (std.mem.eql(u8, name, "svg")) {
+            return true;
+        }
+    }
+    return false;
+}
+
 // area, base, br, col, embed, hr, img, input, link, meta, source, track, wbr
 // https://html.spec.whatwg.org/#void-elements
 fn isVoid(elem: *parser.Element) !bool {
@@ -189,10 +236,10 @@ fn isVoid(elem: *parser.Element) !bool {
     };
 }
 
-fn writeEscapedTextNode(writer: anytype, value: []const u8) !void {
+fn writeEscapedTextNode(writer: *std.Io.Writer, value: []const u8) !void {
     var v = value;
     while (v.len > 0) {
-        const index = std.mem.indexOfAnyPos(u8, v, 0, &.{ '&', '<', '>' }) orelse {
+        const index = std.mem.indexOfAnyPos(u8, v, 0, &.{ '&', '<', '>', 194 }) orelse {
             return writer.writeAll(v);
         };
         try writer.writeAll(v[0..index]);
@@ -200,13 +247,22 @@ fn writeEscapedTextNode(writer: anytype, value: []const u8) !void {
             '&' => try writer.writeAll("&amp;"),
             '<' => try writer.writeAll("&lt;"),
             '>' => try writer.writeAll("&gt;"),
+            194 => {
+                // non breaking space
+                if (v.len > index + 1 and v[index + 1] == 160) {
+                    try writer.writeAll("&nbsp;");
+                    v = v[index + 2 ..];
+                    continue;
+                }
+                try writer.writeByte(194);
+            },
             else => unreachable,
         }
         v = v[index + 1 ..];
     }
 }
 
-fn writeEscapedAttributeValue(writer: anytype, value: []const u8) !void {
+fn writeEscapedAttributeValue(writer: *std.Io.Writer, value: []const u8) !void {
     var v = value;
     while (v.len > 0) {
         const index = std.mem.indexOfAnyPos(u8, v, 0, &.{ '&', '<', '>', '"' }) orelse {
@@ -226,7 +282,7 @@ fn writeEscapedAttributeValue(writer: anytype, value: []const u8) !void {
 
 const testing = std.testing;
 test "dump.writeHTML" {
-    try parser.init();
+    parser.init();
     defer parser.deinit();
 
     try testWriteHTML(

src/browser/encoding/TextDecoder.zig

@@ -19,7 +19,6 @@
 const std = @import("std");
 const log = @import("../../log.zig");
 
-const Env = @import("../env.zig").Env;
 const Page = @import("../page.zig").Page;
 
 // https://encoding.spec.whatwg.org/#interface-textdecoder
@@ -70,8 +69,8 @@ pub fn get_fatal(self: *const TextDecoder) bool {
 const DecodeOptions = struct {
     stream: bool = false,
 };
-pub fn _decode(self: *TextDecoder, input_: ?[]const u8, opts_: ?DecodeOptions, page: *Page) ![]const u8 {
-    var str = input_ orelse return "";
+pub fn _decode(self: *TextDecoder, str_: ?[]const u8, opts_: ?DecodeOptions, page: *Page) ![]const u8 {
+    var str = str_ orelse return "";
     const opts: DecodeOptions = opts_ orelse .{};
 
     if (self.stream.items.len > 0) {

src/browser/encoding/TextEncoder.zig

@@ -18,7 +18,7 @@
 
 const std = @import("std");
 
-const Env = @import("../env.zig").Env;
+const js = @import("../js/js.zig");
 
 // https://encoding.spec.whatwg.org/#interface-textencoder
 const TextEncoder = @This();
@@ -31,7 +31,7 @@ pub fn get_encoding(_: *const TextEncoder) []const u8 {
     return "utf-8";
 }
 
-pub fn _encode(_: *const TextEncoder, v: []const u8) !Env.TypedArray(u8) {
+pub fn _encode(_: *const TextEncoder, v: []const u8) !js.TypedArray(u8) {
     // Ensure the input is a valid utf-8
     // It seems chrome accepts invalid utf-8 sequence.
     //

src/browser/env.zig

@@ -1,49 +0,0 @@
-const std = @import("std");
-
-const Page = @import("page.zig").Page;
-const js = @import("../runtime/js.zig");
-const generate = @import("../runtime/generate.zig");
-
-const WebApis = struct {
-    // Wrapped like this for debug ergonomics.
-    // When we create our Env, a few lines down, we define it as:
-    //   pub const Env = js.Env(*Page, WebApis);
-    //
-    // If there's a compile time error witht he Env, it's type will be readable,
-    // i.e.: runtime.js.Env(*browser.env.Page, browser.env.WebApis)
-    //
-    // But if we didn't wrap it in the struct, like we once didn't, and defined
-    // env as:
-    //   pub const Env = js.Env(*Page, Interfaces);
-    //
-    // Because Interfaces is an anynoumous type, it doesn't have a friendly name
-    // and errors would be something like:
-    //   runtime.js.Env(*browser.Page, .{...A HUNDRED TYPES...})
-    pub const Interfaces = generate.Tuple(.{
-        @import("crypto/crypto.zig").Crypto,
-        @import("console/console.zig").Console,
-        @import("css/css.zig").Interfaces,
-        @import("cssom/cssom.zig").Interfaces,
-        @import("dom/dom.zig").Interfaces,
-        @import("dom/shadow_root.zig").ShadowRoot,
-        @import("encoding/encoding.zig").Interfaces,
-        @import("events/event.zig").Interfaces,
-        @import("html/html.zig").Interfaces,
-        @import("iterator/iterator.zig").Interfaces,
-        @import("storage/storage.zig").Interfaces,
-        @import("url/url.zig").Interfaces,
-        @import("xhr/xhr.zig").Interfaces,
-        @import("xhr/form_data.zig").Interfaces,
-        @import("xhr/File.zig"),
-        @import("xmlserializer/xmlserializer.zig").Interfaces,
-    });
-};
-
-pub const JsThis = Env.JsThis;
-pub const JsObject = Env.JsObject;
-pub const Function = Env.Function;
-pub const Promise = Env.Promise;
-pub const PromiseResolver = Env.PromiseResolver;
-
-pub const Env = js.Env(*Page, WebApis);
-pub const Global = @import("html/window.zig").Window;

src/browser/events/composition_event.zig

@@ -0,0 +1,57 @@
+// Copyright (C) 2023-2025  Lightpanda (Selecy SAS)
+//
+// Francis Bouvier <francis@lightpanda.io>
+// Pierre Tachoire <pierre@lightpanda.io>
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as
+// published by the Free Software Foundation, either version 3 of the
+// License, or (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+const std = @import("std");
+
+const parser = @import("../netsurf.zig");
+
+// https://developer.mozilla.org/en-US/docs/Web/API/CompositionEvent
+pub const CompositionEvent = struct {
+    data: []const u8,
+    proto: parser.Event,
+
+    pub const union_make_copy = true;
+    pub const prototype = *parser.Event;
+
+    pub const ConstructorOptions = struct {
+        data: []const u8 = "",
+    };
+
+    pub fn constructor(event_type: []const u8, options_: ?ConstructorOptions) !CompositionEvent {
+        const options: ConstructorOptions = options_ orelse .{};
+
+        const event = try parser.eventCreate();
+        defer parser.eventDestroy(event);
+        try parser.eventInit(event, event_type, .{});
+        parser.eventSetInternalType(event, .composition_event);
+
+        return .{
+            .proto = event.*,
+            .data = options.data,
+        };
+    }
+
+    pub fn get_data(self: *const CompositionEvent) []const u8 {
+        return self.data;
+    }
+};
+
+const testing = @import("../../testing.zig");
+test "Browser: Events.Composition" {
+    try testing.htmlRunner("events/composition.html");
+}

src/browser/events/custom_event.zig

@@ -16,9 +16,10 @@
 // You should have received a copy of the GNU Affero General Public License
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
+const js = @import("../js/js.zig");
 const parser = @import("../netsurf.zig");
 const Event = @import("event.zig").Event;
-const JsObject = @import("../env.zig").JsObject;
+
 const netsurf = @import("../netsurf.zig");
 
 // https://dom.spec.whatwg.org/#interface-customevent
@@ -27,13 +28,13 @@ pub const CustomEvent = struct {
     pub const union_make_copy = true;
 
     proto: parser.Event,
-    detail: ?JsObject,
+    detail: ?js.Object,
 
     const CustomEventInit = struct {
         bubbles: bool = false,
         cancelable: bool = false,
         composed: bool = false,
-        detail: ?JsObject = null,
+        detail: ?js.Object = null,
     };
 
     pub fn constructor(event_type: []const u8, opts_: ?CustomEventInit) !CustomEvent {
@@ -53,7 +54,7 @@ pub const CustomEvent = struct {
         };
     }
 
-    pub fn get_detail(self: *CustomEvent) ?JsObject {
+    pub fn get_detail(self: *CustomEvent) ?js.Object {
         return self.detail;
     }
 
@@ -64,7 +65,7 @@ pub const CustomEvent = struct {
         event_type: []const u8,
         can_bubble: bool,
         cancelable: bool,
-        maybe_detail: ?JsObject,
+        maybe_detail: ?js.Object,
     ) !void {
         // This function can only be called after the constructor has called.
         // So we assume proto is initialized already by constructor.

src/browser/events/event.zig

@@ -21,7 +21,7 @@ const Allocator = std.mem.Allocator;
 
 const log = @import("../../log.zig");
 const parser = @import("../netsurf.zig");
-const generate = @import("../../runtime/generate.zig");
+const generate = @import("../js/generate.zig");
 
 const Page = @import("../page.zig").Page;
 const Node = @import("../dom/node.zig").Node;
@@ -36,6 +36,8 @@ const MouseEvent = @import("mouse_event.zig").MouseEvent;
 const KeyboardEvent = @import("keyboard_event.zig").KeyboardEvent;
 const ErrorEvent = @import("../html/error_event.zig").ErrorEvent;
 const MessageEvent = @import("../dom/MessageChannel.zig").MessageEvent;
+const PopStateEvent = @import("../html/History.zig").PopStateEvent;
+const CompositionEvent = @import("composition_event.zig").CompositionEvent;
 
 // Event interfaces
 pub const Interfaces = .{
@@ -46,6 +48,8 @@ pub const Interfaces = .{
     KeyboardEvent,
     ErrorEvent,
     MessageEvent,
+    PopStateEvent,
+    CompositionEvent,
 };
 
 pub const Union = generate.Union(Interfaces);
@@ -70,9 +74,11 @@ pub const Event = struct {
             .custom_event => .{ .CustomEvent = @as(*CustomEvent, @ptrCast(evt)).* },
             .progress_event => .{ .ProgressEvent = @as(*ProgressEvent, @ptrCast(evt)).* },
             .mouse_event => .{ .MouseEvent = @as(*parser.MouseEvent, @ptrCast(evt)) },
-            .error_event => .{ .ErrorEvent = @as(*ErrorEvent, @ptrCast(evt)).* },
+            .error_event => .{ .ErrorEvent = (@as(*ErrorEvent, @fieldParentPtr("proto", evt))).* },
             .message_event => .{ .MessageEvent = @as(*MessageEvent, @ptrCast(evt)).* },
             .keyboard_event => .{ .KeyboardEvent = @as(*parser.KeyboardEvent, @ptrCast(evt)) },
+            .pop_state => .{ .PopStateEvent = @as(*PopStateEvent, @ptrCast(evt)).* },
+            .composition_event => .{ .CompositionEvent = (@as(*CompositionEvent, @fieldParentPtr("proto", evt))).* },
         };
     }
 
@@ -84,8 +90,8 @@ pub const Event = struct {
 
     // Getters
 
-    pub fn get_type(self: *parser.Event) ![]const u8 {
-        return try parser.eventType(self);
+    pub fn get_type(self: *parser.Event) []const u8 {
+        return parser.eventType(self);
     }
 
     pub fn get_target(self: *parser.Event, page: *Page) !?EventTargetUnion {
@@ -158,7 +164,7 @@ pub const Event = struct {
         const et_ = parser.eventTarget(self);
         const et = et_ orelse return &.{};
 
-        var node: ?*parser.Node = switch (try parser.eventTargetInternalType(et)) {
+        var node: ?*parser.Node = switch (parser.eventTargetInternalType(et)) {
             .libdom_node => @as(*parser.Node, @ptrCast(et)),
             .plain => parser.eventTargetToNode(et),
             else => {
@@ -174,8 +180,8 @@ pub const Event = struct {
                 .node = try Node.toInterface(n),
             });
 
-            node = try parser.nodeParentNode(n);
-            if (node == null and try parser.nodeType(n) == .document_fragment) {
+            node = parser.nodeParentNode(n);
+            if (node == null and parser.nodeType(n) == .document_fragment) {
                 // we have a non-continuous hook from a shadowroot to its host (
                 // it's parent element). libdom doesn't really support ShdowRoots
                 // and, for the most part, that works out well since it naturally
@@ -216,18 +222,17 @@ pub const Event = struct {
 pub const EventHandler = struct {
     once: bool,
     capture: bool,
-    callback: Function,
+    callback: js.Function,
     node: parser.EventNode,
     listener: *parser.EventListener,
 
-    const Env = @import("../env.zig").Env;
-    const Function = Env.Function;
+    const js = @import("../js/js.zig");
 
     pub const Listener = union(enum) {
-        function: Function,
-        object: Env.JsObject,
+        function: js.Function,
+        object: js.Object,
 
-        pub fn callback(self: Listener, target: *parser.EventTarget) !?Function {
+        pub fn callback(self: Listener, target: *parser.EventTarget) !?js.Function {
             return switch (self) {
                 .function => |func| try func.withThis(target),
                 .object => |obj| blk: {
@@ -328,7 +333,7 @@ pub const EventHandler = struct {
     fn handle(node: *parser.EventNode, event: *parser.Event) void {
         const ievent = Event.toInterface(event);
         const self: *EventHandler = @fieldParentPtr("node", node);
-        var result: Function.Result = undefined;
+        var result: js.Function.Result = undefined;
         self.callback.tryCall(void, .{ievent}, &result) catch {
             log.debug(.user_script, "callback error", .{
                 .err = result.exception,
@@ -339,7 +344,7 @@ pub const EventHandler = struct {
 
         if (self.once) {
             const target = parser.eventTarget(event).?;
-            const typ = parser.eventType(event) catch return;
+            const typ = parser.eventType(event);
             parser.eventTargetRemoveEventListener(
                 target,
                 typ,

src/browser/events/keyboard_event.zig

@@ -22,7 +22,6 @@ const builtin = @import("builtin");
 
 const parser = @import("../netsurf.zig");
 const Event = @import("event.zig").Event;
-const JsObject = @import("../env.zig").JsObject;
 
 // TODO: We currently don't have a UIEvent interface so we skip it in the prototype chain.
 // https://developer.mozilla.org/en-US/docs/Web/API/UIEvent
@@ -54,8 +53,8 @@ pub const KeyboardEvent = struct {
     pub fn constructor(event_type: []const u8, maybe_options: ?ConstructorOptions) !*parser.KeyboardEvent {
         const options: ConstructorOptions = maybe_options orelse .{};
 
-        var event = try parser.keyboardEventCreate();
-        parser.eventSetInternalType(@ptrCast(&event), .keyboard_event);
+        const event = try parser.keyboardEventCreate();
+        parser.eventSetInternalType(@ptrCast(event), .keyboard_event);
 
         try parser.keyboardEventInit(
             event,

src/browser/events/mouse_event.zig

@@ -21,7 +21,6 @@ const log = @import("../../log.zig");
 
 const parser = @import("../netsurf.zig");
 const Event = @import("event.zig").Event;
-const JsObject = @import("../env.zig").JsObject;
 
 // TODO: We currently don't have a UIEvent interface so we skip it in the prototype chain.
 // https://developer.mozilla.org/en-US/docs/Web/API/UIEvent
@@ -55,8 +54,8 @@ pub const MouseEvent = struct {
     pub fn constructor(event_type: []const u8, opts_: ?MouseEventInit) !*parser.MouseEvent {
         const opts = opts_ orelse MouseEventInit{};
 
-        var mouse_event = try parser.mouseEventCreate();
-        parser.eventSetInternalType(@ptrCast(&mouse_event), .mouse_event);
+        const mouse_event = try parser.mouseEventCreate();
+        parser.eventSetInternalType(@ptrCast(mouse_event), .mouse_event);
 
         try parser.mouseEventInit(mouse_event, event_type, .{
             .x = opts.clientX,
@@ -69,7 +68,7 @@ pub const MouseEvent = struct {
         });
 
         if (!std.mem.eql(u8, event_type, "click")) {
-            log.warn(.mouse_event, "unsupported mouse event", .{ .event = event_type });
+            log.warn(.browser, "unsupported mouse event", .{ .event = event_type });
         }
 
         return mouse_event;

src/browser/fetch/Headers.zig

@@ -0,0 +1,225 @@
+// Copyright (C) 2023-2024  Lightpanda (Selecy SAS)
+//
+// Francis Bouvier <francis@lightpanda.io>
+// Pierre Tachoire <pierre@lightpanda.io>
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as
+// published by the Free Software Foundation, either version 3 of the
+// License, or (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+const std = @import("std");
+const js = @import("../js/js.zig");
+const log = @import("../../log.zig");
+const URL = @import("../../url.zig").URL;
+const Page = @import("../page.zig").Page;
+
+const iterator = @import("../iterator/iterator.zig");
+
+// https://developer.mozilla.org/en-US/docs/Web/API/Headers
+const Headers = @This();
+
+// Case-Insensitive String HashMap.
+// This allows us to avoid having to allocate lowercase keys all the time.
+const HeaderHashMap = std.HashMapUnmanaged([]const u8, []const u8, struct {
+    pub fn hash(_: @This(), s: []const u8) u64 {
+        var buf: [64]u8 = undefined;
+        var hasher = std.hash.Wyhash.init(s.len);
+
+        var key = s;
+        while (key.len >= 64) {
+            const lower = std.ascii.lowerString(buf[0..], key[0..64]);
+            hasher.update(lower);
+            key = key[64..];
+        }
+
+        if (key.len > 0) {
+            const lower = std.ascii.lowerString(buf[0..key.len], key);
+            hasher.update(lower);
+        }
+
+        return hasher.final();
+    }
+
+    pub fn eql(_: @This(), a: []const u8, b: []const u8) bool {
+        return std.ascii.eqlIgnoreCase(a, b);
+    }
+}, 80);
+
+headers: HeaderHashMap = .empty,
+
+// They can either be:
+//
+// 1. An array of string pairs.
+// 2. An object with string keys to string values.
+// 3. Another Headers object.
+pub const HeadersInit = union(enum) {
+    // List of Pairs of []const u8
+    strings: []const [2][]const u8,
+    // Headers
+    headers: *Headers,
+    // Mappings
+    object: js.Object,
+};
+
+pub fn constructor(_init: ?HeadersInit, page: *Page) !Headers {
+    const arena = page.arena;
+    var headers: HeaderHashMap = .empty;
+
+    if (_init) |init| {
+        switch (init) {
+            .strings => |kvs| {
+                for (kvs) |pair| {
+                    const key = try arena.dupe(u8, pair[0]);
+                    const value = try arena.dupe(u8, pair[1]);
+
+                    try headers.put(arena, key, value);
+                }
+            },
+            .headers => |hdrs| {
+                var iter = hdrs.headers.iterator();
+                while (iter.next()) |entry| {
+                    try headers.put(arena, entry.key_ptr.*, entry.value_ptr.*);
+                }
+            },
+            .object => |obj| {
+                var iter = obj.nameIterator();
+                while (try iter.next()) |name_value| {
+                    const name = try name_value.toString(arena);
+                    const value = try obj.get(name);
+                    const value_string = try value.toString(arena);
+
+                    try headers.put(arena, name, value_string);
+                }
+            },
+        }
+    }
+
+    return .{
+        .headers = headers,
+    };
+}
+
+pub fn append(self: *Headers, name: []const u8, value: []const u8, allocator: std.mem.Allocator) !void {
+    const key = try allocator.dupe(u8, name);
+    const gop = try self.headers.getOrPut(allocator, key);
+
+    if (gop.found_existing) {
+        // If we found it, append the value.
+        const new_value = try std.fmt.allocPrint(allocator, "{s}, {s}", .{ gop.value_ptr.*, value });
+        gop.value_ptr.* = new_value;
+    } else {
+        // Otherwise, we should just put it in.
+        gop.value_ptr.* = try allocator.dupe(u8, value);
+    }
+}
+
+pub fn _append(self: *Headers, name: []const u8, value: []const u8, page: *Page) !void {
+    const arena = page.arena;
+    try self.append(name, value, arena);
+}
+
+pub fn _delete(self: *Headers, name: []const u8) void {
+    _ = self.headers.remove(name);
+}
+
+pub const HeadersEntryIterator = struct {
+    slot: [2][]const u8,
+    iter: HeaderHashMap.Iterator,
+
+    // TODO: these SHOULD be in lexigraphical order but I'm not sure how actually
+    // important that is.
+    pub fn _next(self: *HeadersEntryIterator) ?[2][]const u8 {
+        if (self.iter.next()) |entry| {
+            self.slot[0] = entry.key_ptr.*;
+            self.slot[1] = entry.value_ptr.*;
+            return self.slot;
+        } else {
+            return null;
+        }
+    }
+};
+
+pub fn _entries(self: *const Headers) HeadersEntryIterable {
+    return .{
+        .inner = .{
+            .slot = undefined,
+            .iter = self.headers.iterator(),
+        },
+    };
+}
+
+pub fn _forEach(self: *Headers, callback_fn: js.Function, this_arg: ?js.Object) !void {
+    var iter = self.headers.iterator();
+
+    const cb = if (this_arg) |this| try callback_fn.withThis(this) else callback_fn;
+
+    while (iter.next()) |entry| {
+        try cb.call(void, .{ entry.key_ptr.*, entry.value_ptr.*, self });
+    }
+}
+
+pub fn _get(self: *const Headers, name: []const u8) ?[]const u8 {
+    return self.headers.get(name);
+}
+
+pub fn _has(self: *const Headers, name: []const u8) bool {
+    return self.headers.contains(name);
+}
+
+pub const HeadersKeyIterator = struct {
+    iter: HeaderHashMap.KeyIterator,
+
+    pub fn _next(self: *HeadersKeyIterator) ?[]const u8 {
+        if (self.iter.next()) |key| {
+            return key.*;
+        } else {
+            return null;
+        }
+    }
+};
+
+pub fn _keys(self: *const Headers) HeadersKeyIterable {
+    return .{ .inner = .{ .iter = self.headers.keyIterator() } };
+}
+
+pub fn _set(self: *Headers, name: []const u8, value: []const u8, page: *Page) !void {
+    const arena = page.arena;
+
+    const key = try arena.dupe(u8, name);
+    const gop = try self.headers.getOrPut(arena, key);
+    gop.value_ptr.* = try arena.dupe(u8, value);
+}
+
+pub const HeadersValueIterator = struct {
+    iter: HeaderHashMap.ValueIterator,
+
+    pub fn _next(self: *HeadersValueIterator) ?[]const u8 {
+        if (self.iter.next()) |value| {
+            return value.*;
+        } else {
+            return null;
+        }
+    }
+};
+
+pub fn _values(self: *const Headers) HeadersValueIterable {
+    return .{ .inner = .{ .iter = self.headers.valueIterator() } };
+}
+
+pub const HeadersKeyIterable = iterator.Iterable(HeadersKeyIterator, "HeadersKeyIterator");
+pub const HeadersValueIterable = iterator.Iterable(HeadersValueIterator, "HeadersValueIterator");
+pub const HeadersEntryIterable = iterator.Iterable(HeadersEntryIterator, "HeadersEntryIterator");
+
+const testing = @import("../../testing.zig");
+test "fetch: Headers" {
+    try testing.htmlRunner("fetch/headers.html");
+}

src/browser/fetch/Request.zig

@@ -0,0 +1,283 @@
+// Copyright (C) 2023-2024  Lightpanda (Selecy SAS)
+//
+// Francis Bouvier <francis@lightpanda.io>
+// Pierre Tachoire <pierre@lightpanda.io>
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as
+// published by the Free Software Foundation, either version 3 of the
+// License, or (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+const std = @import("std");
+const js = @import("../js/js.zig");
+const log = @import("../../log.zig");
+
+const URL = @import("../../url.zig").URL;
+const Page = @import("../page.zig").Page;
+
+const Response = @import("./Response.zig");
+const Http = @import("../../http/Http.zig");
+const ReadableStream = @import("../streams/ReadableStream.zig");
+
+const Headers = @import("Headers.zig");
+const HeadersInit = @import("Headers.zig").HeadersInit;
+
+pub const RequestInput = union(enum) {
+    string: []const u8,
+    request: *Request,
+};
+
+pub const RequestCache = enum {
+    default,
+    @"no-store",
+    reload,
+    @"no-cache",
+    @"force-cache",
+    @"only-if-cached",
+
+    pub fn fromString(str: []const u8) ?RequestCache {
+        for (std.enums.values(RequestCache)) |cache| {
+            if (std.ascii.eqlIgnoreCase(str, @tagName(cache))) {
+                return cache;
+            }
+        } else {
+            return null;
+        }
+    }
+
+    pub fn toString(self: RequestCache) []const u8 {
+        return @tagName(self);
+    }
+};
+
+pub const RequestCredentials = enum {
+    omit,
+    @"same-origin",
+    include,
+
+    pub fn fromString(str: []const u8) ?RequestCredentials {
+        for (std.enums.values(RequestCredentials)) |cache| {
+            if (std.ascii.eqlIgnoreCase(str, @tagName(cache))) {
+                return cache;
+            }
+        } else {
+            return null;
+        }
+    }
+
+    pub fn toString(self: RequestCredentials) []const u8 {
+        return @tagName(self);
+    }
+};
+
+pub const RequestMode = enum {
+    cors,
+    @"no-cors",
+    @"same-origin",
+    navigate,
+
+    pub fn fromString(str: []const u8) ?RequestMode {
+        for (std.enums.values(RequestMode)) |cache| {
+            if (std.ascii.eqlIgnoreCase(str, @tagName(cache))) {
+                return cache;
+            }
+        } else {
+            return null;
+        }
+    }
+
+    pub fn toString(self: RequestMode) []const u8 {
+        return @tagName(self);
+    }
+};
+
+// https://developer.mozilla.org/en-US/docs/Web/API/RequestInit
+pub const RequestInit = struct {
+    body: ?[]const u8 = null,
+    cache: ?[]const u8 = null,
+    credentials: ?[]const u8 = null,
+    headers: ?HeadersInit = null,
+    integrity: ?[]const u8 = null,
+    method: ?[]const u8 = null,
+    mode: ?[]const u8 = null,
+};
+
+// https://developer.mozilla.org/en-US/docs/Web/API/Request/Request
+const Request = @This();
+
+method: Http.Method,
+url: [:0]const u8,
+cache: RequestCache,
+credentials: RequestCredentials,
+// no-cors is default is not built with constructor.
+mode: RequestMode = .@"no-cors",
+headers: Headers,
+body: ?[]const u8,
+body_used: bool = false,
+integrity: []const u8,
+
+pub fn constructor(input: RequestInput, _options: ?RequestInit, page: *Page) !Request {
+    const arena = page.arena;
+    const options: RequestInit = _options orelse .{};
+
+    const url: [:0]const u8 = blk: switch (input) {
+        .string => |str| {
+            break :blk try URL.stitch(arena, str, page.url.raw, .{ .null_terminated = true });
+        },
+        .request => |req| {
+            break :blk try arena.dupeZ(u8, req.url);
+        },
+    };
+
+    const cache = (if (options.cache) |cache| RequestCache.fromString(cache) else null) orelse RequestCache.default;
+    const credentials = (if (options.credentials) |creds| RequestCredentials.fromString(creds) else null) orelse RequestCredentials.@"same-origin";
+    const integrity = if (options.integrity) |integ| try arena.dupe(u8, integ) else "";
+    const headers: Headers = if (options.headers) |hdrs| try Headers.constructor(hdrs, page) else .{};
+    const mode = (if (options.mode) |mode| RequestMode.fromString(mode) else null) orelse RequestMode.cors;
+
+    const method: Http.Method = blk: {
+        if (options.method) |given_method| {
+            for (std.enums.values(Http.Method)) |method| {
+                if (std.ascii.eqlIgnoreCase(given_method, @tagName(method))) {
+                    break :blk method;
+                }
+            } else {
+                return error.TypeError;
+            }
+        } else {
+            break :blk Http.Method.GET;
+        }
+    };
+
+    // Can't have a body on .GET or .HEAD.
+    const body: ?[]const u8 = blk: {
+        if (method == .GET or method == .HEAD) {
+            break :blk null;
+        } else break :blk if (options.body) |body| try arena.dupe(u8, body) else null;
+    };
+
+    return .{
+        .method = method,
+        .url = url,
+        .cache = cache,
+        .credentials = credentials,
+        .mode = mode,
+        .headers = headers,
+        .body = body,
+        .integrity = integrity,
+    };
+}
+
+pub fn get_body(self: *const Request, page: *Page) !?*ReadableStream {
+    if (self.body) |body| {
+        const stream = try ReadableStream.constructor(null, null, page);
+        try stream.queue.append(page.arena, .{ .string = body });
+        return stream;
+    } else return null;
+}
+
+pub fn get_bodyUsed(self: *const Request) bool {
+    return self.body_used;
+}
+
+pub fn get_cache(self: *const Request) RequestCache {
+    return self.cache;
+}
+
+pub fn get_credentials(self: *const Request) RequestCredentials {
+    return self.credentials;
+}
+
+pub fn get_headers(self: *Request) *Headers {
+    return &self.headers;
+}
+
+pub fn get_integrity(self: *const Request) []const u8 {
+    return self.integrity;
+}
+
+// TODO: If we ever support the Navigation API, we need isHistoryNavigation
+// https://developer.mozilla.org/en-US/docs/Web/API/Request/isHistoryNavigation
+
+pub fn get_method(self: *const Request) []const u8 {
+    return @tagName(self.method);
+}
+
+pub fn get_mode(self: *const Request) RequestMode {
+    return self.mode;
+}
+
+pub fn get_url(self: *const Request) []const u8 {
+    return self.url;
+}
+
+pub fn _clone(self: *Request) !Request {
+    // Not allowed to clone if the body was used.
+    if (self.body_used) {
+        return error.TypeError;
+    }
+
+    // OK to just return the same fields BECAUSE
+    // all of these fields are read-only and can't be modified.
+    return Request{
+        .body = self.body,
+        .body_used = self.body_used,
+        .cache = self.cache,
+        .credentials = self.credentials,
+        .headers = self.headers,
+        .method = self.method,
+        .integrity = self.integrity,
+        .url = self.url,
+    };
+}
+
+pub fn _bytes(self: *Response, page: *Page) !js.Promise {
+    if (self.body_used) {
+        return error.TypeError;
+    }
+    self.body_used = true;
+    return page.js.resolvePromise(self.body);
+}
+
+pub fn _json(self: *Response, page: *Page) !js.Promise {
+    if (self.body_used) {
+        return error.TypeError;
+    }
+    self.body_used = true;
+
+    if (self.body) |body| {
+        const p = std.json.parseFromSliceLeaky(
+            std.json.Value,
+            page.call_arena,
+            body,
+            .{},
+        ) catch |e| {
+            log.info(.browser, "invalid json", .{ .err = e, .source = "Request" });
+            return error.SyntaxError;
+        };
+
+        return page.js.resolvePromise(p);
+    }
+    return page.js.resolvePromise(null);
+}
+
+pub fn _text(self: *Response, page: *Page) !js.Promise {
+    if (self.body_used) {
+        return error.TypeError;
+    }
+    self.body_used = true;
+    return page.js.resolvePromise(self.body);
+}
+
+const testing = @import("../../testing.zig");
+test "fetch: Request" {
+    try testing.htmlRunner("fetch/request.html");
+}

src/browser/fetch/Response.zig

@@ -0,0 +1,209 @@
+// Copyright (C) 2023-2024  Lightpanda (Selecy SAS)
+//
+// Francis Bouvier <francis@lightpanda.io>
+// Pierre Tachoire <pierre@lightpanda.io>
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as
+// published by the Free Software Foundation, either version 3 of the
+// License, or (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+const std = @import("std");
+const js = @import("../js/js.zig");
+const log = @import("../../log.zig");
+
+const HttpClient = @import("../../http/Client.zig");
+const Http = @import("../../http/Http.zig");
+const URL = @import("../../url.zig").URL;
+
+const ReadableStream = @import("../streams/ReadableStream.zig");
+const Headers = @import("Headers.zig");
+const HeadersInit = @import("Headers.zig").HeadersInit;
+
+const Mime = @import("../mime.zig").Mime;
+const Page = @import("../page.zig").Page;
+
+// https://developer.mozilla.org/en-US/docs/Web/API/Response
+const Response = @This();
+
+status: u16 = 200,
+status_text: []const u8 = "",
+headers: Headers,
+mime: ?Mime = null,
+url: []const u8 = "",
+body: ?[]const u8 = null,
+body_used: bool = false,
+redirected: bool = false,
+type: ResponseType = .basic,
+
+const ResponseBody = union(enum) {
+    string: []const u8,
+};
+
+const ResponseOptions = struct {
+    status: u16 = 200,
+    statusText: ?[]const u8 = null,
+    headers: ?HeadersInit = null,
+};
+
+pub const ResponseType = enum {
+    basic,
+    cors,
+    @"error",
+    @"opaque",
+    opaqueredirect,
+
+    pub fn fromString(str: []const u8) ?ResponseType {
+        for (std.enums.values(ResponseType)) |cache| {
+            if (std.ascii.eqlIgnoreCase(str, @tagName(cache))) {
+                return cache;
+            }
+        } else {
+            return null;
+        }
+    }
+
+    pub fn toString(self: ResponseType) []const u8 {
+        return @tagName(self);
+    }
+};
+
+pub fn constructor(_input: ?ResponseBody, _options: ?ResponseOptions, page: *Page) !Response {
+    const arena = page.arena;
+
+    const options: ResponseOptions = _options orelse .{};
+
+    const body = blk: {
+        if (_input) |input| {
+            switch (input) {
+                .string => |str| {
+                    break :blk try arena.dupe(u8, str);
+                },
+            }
+        } else {
+            break :blk null;
+        }
+    };
+
+    const headers: Headers = if (options.headers) |hdrs| try Headers.constructor(hdrs, page) else .{};
+    const status_text = if (options.statusText) |st| try arena.dupe(u8, st) else "";
+
+    return .{
+        .body = body,
+        .headers = headers,
+        .status = options.status,
+        .status_text = status_text,
+    };
+}
+
+pub fn get_body(self: *const Response, page: *Page) !*ReadableStream {
+    const stream = try ReadableStream.constructor(null, null, page);
+    if (self.body) |body| {
+        try stream.queue.append(page.arena, .{ .string = body });
+    }
+    return stream;
+}
+
+pub fn get_bodyUsed(self: *const Response) bool {
+    return self.body_used;
+}
+
+pub fn get_headers(self: *Response) *Headers {
+    return &self.headers;
+}
+
+pub fn get_ok(self: *const Response) bool {
+    return self.status >= 200 and self.status <= 299;
+}
+
+pub fn get_redirected(self: *const Response) bool {
+    return self.redirected;
+}
+
+pub fn get_status(self: *const Response) u16 {
+    return self.status;
+}
+
+pub fn get_statusText(self: *const Response) []const u8 {
+    return self.status_text;
+}
+
+pub fn get_type(self: *const Response) ResponseType {
+    return self.type;
+}
+
+pub fn get_url(self: *const Response) []const u8 {
+    return self.url;
+}
+
+pub fn _clone(self: *const Response) !Response {
+    if (self.body_used) {
+        return error.TypeError;
+    }
+
+    // OK to just return the same fields BECAUSE
+    // all of these fields are read-only and can't be modified.
+    return Response{
+        .body = self.body,
+        .body_used = self.body_used,
+        .mime = self.mime,
+        .headers = self.headers,
+        .redirected = self.redirected,
+        .status = self.status,
+        .url = self.url,
+        .type = self.type,
+    };
+}
+
+pub fn _bytes(self: *Response, page: *Page) !js.Promise {
+    if (self.body_used) {
+        return error.TypeError;
+    }
+
+    self.body_used = true;
+    return page.js.resolvePromise(self.body);
+}
+
+pub fn _json(self: *Response, page: *Page) !js.Promise {
+    if (self.body_used) {
+        return error.TypeError;
+    }
+
+    if (self.body) |body| {
+        self.body_used = true;
+        const p = std.json.parseFromSliceLeaky(
+            std.json.Value,
+            page.call_arena,
+            body,
+            .{},
+        ) catch |e| {
+            log.info(.browser, "invalid json", .{ .err = e, .source = "Response" });
+            return error.SyntaxError;
+        };
+
+        return page.js.resolvePromise(p);
+    }
+    return page.js.resolvePromise(null);
+}
+
+pub fn _text(self: *Response, page: *Page) !js.Promise {
+    if (self.body_used) {
+        return error.TypeError;
+    }
+    self.body_used = true;
+
+    return page.js.resolvePromise(self.body);
+}
+
+const testing = @import("../../testing.zig");
+test "fetch: Response" {
+    try testing.htmlRunner("fetch/response.html");
+}

src/browser/fetch/fetch.zig

@@ -0,0 +1,243 @@
+// Copyright (C) 2023-2024  Lightpanda (Selecy SAS)
+//
+// Francis Bouvier <francis@lightpanda.io>
+// Pierre Tachoire <pierre@lightpanda.io>
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as
+// published by the Free Software Foundation, either version 3 of the
+// License, or (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+const std = @import("std");
+const log = @import("../../log.zig");
+
+const js = @import("../js/js.zig");
+const Page = @import("../page.zig").Page;
+
+const Http = @import("../../http/Http.zig");
+const HttpClient = @import("../../http/Client.zig");
+const Mime = @import("../mime.zig").Mime;
+
+const Headers = @import("Headers.zig");
+
+const RequestInput = @import("Request.zig").RequestInput;
+const RequestInit = @import("Request.zig").RequestInit;
+const Request = @import("Request.zig");
+const Response = @import("Response.zig");
+
+pub const Interfaces = .{
+    @import("Headers.zig"),
+    @import("Headers.zig").HeadersEntryIterable,
+    @import("Headers.zig").HeadersKeyIterable,
+    @import("Headers.zig").HeadersValueIterable,
+    @import("Request.zig"),
+    @import("Response.zig"),
+};
+
+pub const FetchContext = struct {
+    page: *Page,
+    arena: std.mem.Allocator,
+    promise_resolver: js.PersistentPromiseResolver,
+
+    method: Http.Method,
+    url: []const u8,
+    body: std.ArrayListUnmanaged(u8) = .empty,
+    headers: std.ArrayListUnmanaged([]const u8) = .empty,
+    status: u16 = 0,
+    mime: ?Mime = null,
+    mode: Request.RequestMode,
+    transfer: ?*HttpClient.Transfer = null,
+
+    /// This effectively takes ownership of the FetchContext.
+    ///
+    /// We just return the underlying slices used for `headers`
+    /// and for `body` here to avoid an allocation.
+    pub fn toResponse(self: *const FetchContext) !Response {
+        var headers: Headers = .{};
+
+        // seems to be the highest priority
+        const same_origin = try self.page.isSameOrigin(self.url);
+
+        // If the mode is "no-cors", we need to return this opaque/stripped Response.
+        // https://developer.mozilla.org/en-US/docs/Web/API/Response/type
+        if (!same_origin and self.mode == .@"no-cors") {
+            return Response{
+                .status = 0,
+                .headers = headers,
+                .mime = self.mime,
+                .body = null,
+                .url = self.url,
+                .type = .@"opaque",
+            };
+        }
+
+        // convert into Headers
+        for (self.headers.items) |hdr| {
+            var iter = std.mem.splitScalar(u8, hdr, ':');
+            const name = iter.next() orelse "";
+            const value = iter.next() orelse "";
+            try headers.append(name, value, self.arena);
+        }
+
+        const resp_type: Response.ResponseType = blk: {
+            if (same_origin or std.mem.startsWith(u8, self.url, "data:")) {
+                break :blk .basic;
+            }
+
+            break :blk switch (self.mode) {
+                .cors => .cors,
+                .@"same-origin", .navigate => .basic,
+                .@"no-cors" => unreachable,
+            };
+        };
+
+        return Response{
+            .status = self.status,
+            .headers = headers,
+            .mime = self.mime,
+            .body = self.body.items,
+            .url = self.url,
+            .type = resp_type,
+        };
+    }
+};
+
+// https://developer.mozilla.org/en-US/docs/Web/API/Window/fetch
+pub fn fetch(input: RequestInput, options: ?RequestInit, page: *Page) !js.Promise {
+    const arena = page.arena;
+
+    const req = try Request.constructor(input, options, page);
+    var headers = try page.http_client.newHeaders();
+
+    // Copy our headers into the HTTP headers.
+    var header_iter = req.headers.headers.iterator();
+    while (header_iter.next()) |entry| {
+        const combined = try std.fmt.allocPrintSentinel(
+            page.arena,
+            "{s}: {s}",
+            .{ entry.key_ptr.*, entry.value_ptr.* },
+            0,
+        );
+        try headers.add(combined.ptr);
+    }
+
+    try page.requestCookie(.{}).headersForRequest(arena, req.url, &headers);
+
+    const resolver = try page.js.createPromiseResolver(.page);
+
+    const fetch_ctx = try arena.create(FetchContext);
+    fetch_ctx.* = .{
+        .page = page,
+        .arena = arena,
+        .promise_resolver = resolver,
+        .method = req.method,
+        .url = req.url,
+        .mode = req.mode,
+    };
+
+    try page.http_client.request(.{
+        .ctx = @ptrCast(fetch_ctx),
+        .url = req.url,
+        .method = req.method,
+        .headers = headers,
+        .body = req.body,
+        .cookie_jar = page.cookie_jar,
+        .resource_type = .fetch,
+
+        .start_callback = struct {
+            fn startCallback(transfer: *HttpClient.Transfer) !void {
+                const self: *FetchContext = @ptrCast(@alignCast(transfer.ctx));
+                log.debug(.fetch, "request start", .{ .method = self.method, .url = self.url, .source = "fetch" });
+
+                self.transfer = transfer;
+            }
+        }.startCallback,
+        .header_callback = struct {
+            fn headerCallback(transfer: *HttpClient.Transfer) !void {
+                const self: *FetchContext = @ptrCast(@alignCast(transfer.ctx));
+
+                const header = &transfer.response_header.?;
+
+                log.debug(.fetch, "request header", .{
+                    .source = "fetch",
+                    .method = self.method,
+                    .url = self.url,
+                    .status = header.status,
+                });
+
+                if (header.contentType()) |ct| {
+                    self.mime = Mime.parse(ct) catch {
+                        return error.MimeParsing;
+                    };
+                }
+
+                if (transfer.getContentLength()) |cl| {
+                    try self.body.ensureTotalCapacity(self.arena, cl);
+                }
+
+                var it = transfer.responseHeaderIterator();
+                while (it.next()) |hdr| {
+                    const joined = try std.fmt.allocPrint(self.arena, "{s}: {s}", .{ hdr.name, hdr.value });
+                    try self.headers.append(self.arena, joined);
+                }
+
+                self.status = header.status;
+            }
+        }.headerCallback,
+        .data_callback = struct {
+            fn dataCallback(transfer: *HttpClient.Transfer, data: []const u8) !void {
+                const self: *FetchContext = @ptrCast(@alignCast(transfer.ctx));
+                try self.body.appendSlice(self.arena, data);
+            }
+        }.dataCallback,
+        .done_callback = struct {
+            fn doneCallback(ctx: *anyopaque) !void {
+                const self: *FetchContext = @ptrCast(@alignCast(ctx));
+                self.transfer = null;
+
+                log.info(.fetch, "request complete", .{
+                    .source = "fetch",
+                    .method = self.method,
+                    .url = self.url,
+                    .status = self.status,
+                });
+
+                const response = try self.toResponse();
+                try self.promise_resolver.resolve(response);
+            }
+        }.doneCallback,
+        .error_callback = struct {
+            fn errorCallback(ctx: *anyopaque, err: anyerror) void {
+                const self: *FetchContext = @ptrCast(@alignCast(ctx));
+                self.transfer = null;
+
+                log.err(.fetch, "error", .{
+                    .url = self.url,
+                    .err = err,
+                    .source = "fetch error",
+                });
+
+                // We throw an Abort error when the page is getting closed so,
+                // in this case, we don't need to reject the promise.
+                if (err != error.Abort) {
+                    self.promise_resolver.reject(@errorName(err)) catch unreachable;
+                }
+            }
+        }.errorCallback,
+    });
+
+    return resolver.promise();
+}
+
+const testing = @import("../../testing.zig");
+test "fetch: fetch" {
+    try testing.htmlRunner("fetch/fetch.html");
+}

src/browser/html/AbortController.zig

@@ -17,9 +17,9 @@
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 const std = @import("std");
+const js = @import("../js/js.zig");
 const log = @import("../../log.zig");
 const parser = @import("../netsurf.zig");
-const Env = @import("../env.zig").Env;
 const Page = @import("../page.zig").Page;
 const EventTarget = @import("../dom/event_target.zig").EventTarget;
 
@@ -113,12 +113,12 @@ pub const AbortSignal = struct {
     }
 
     const ThrowIfAborted = union(enum) {
-        exception: Env.Exception,
+        exception: js.Exception,
         undefined: void,
     };
     pub fn _throwIfAborted(self: *const AbortSignal, page: *Page) ThrowIfAborted {
         if (self.aborted) {
-            const ex = page.main_context.throw(self.reason orelse DEFAULT_REASON);
+            const ex = page.js.throw(self.reason orelse DEFAULT_REASON);
             return .{ .exception = ex };
         }
         return .{ .undefined = {} };

src/browser/html/DataSet.zig

@@ -17,7 +17,8 @@
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.
 const std = @import("std");
 const parser = @import("../netsurf.zig");
-const Env = @import("../env.zig").Env;
+const js = @import("../js/js.zig");
+
 const Page = @import("../page.zig").Page;
 
 const Allocator = std.mem.Allocator;
@@ -26,7 +27,7 @@ const DataSet = @This();
 
 element: *parser.Element,
 
-pub fn named_get(self: *const DataSet, name: []const u8, _: *bool, page: *Page) !Env.UndefinedOr([]const u8) {
+pub fn named_get(self: *const DataSet, name: []const u8, _: *bool, page: *Page) !js.UndefinedOr([]const u8) {
     const normalized_name = try normalize(page.call_arena, name);
     if (try parser.elementGetAttribute(self.element, normalized_name)) |value| {
         return .{ .value = value };

src/browser/html/History.zig

@@ -0,0 +1,215 @@
+// Copyright (C) 2023-2024  Lightpanda (Selecy SAS)
+//
+// Francis Bouvier <francis@lightpanda.io>
+// Pierre Tachoire <pierre@lightpanda.io>
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as
+// published by the Free Software Foundation, either version 3 of the
+// License, or (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+const std = @import("std");
+const log = @import("../../log.zig");
+
+const js = @import("../js/js.zig");
+const Page = @import("../page.zig").Page;
+
+// https://html.spec.whatwg.org/multipage/nav-history-apis.html#the-history-interface
+const History = @This();
+
+const HistoryEntry = struct {
+    url: []const u8,
+    // This is serialized as JSON because
+    // History must survive a JsContext.
+    state: ?[]u8,
+};
+
+const ScrollRestorationMode = enum {
+    auto,
+    manual,
+
+    pub fn fromString(str: []const u8) ?ScrollRestorationMode {
+        for (std.enums.values(ScrollRestorationMode)) |mode| {
+            if (std.ascii.eqlIgnoreCase(str, @tagName(mode))) {
+                return mode;
+            }
+        } else {
+            return null;
+        }
+    }
+
+    pub fn toString(self: ScrollRestorationMode) []const u8 {
+        return @tagName(self);
+    }
+};
+
+scroll_restoration: ScrollRestorationMode = .auto,
+stack: std.ArrayListUnmanaged(HistoryEntry) = .empty,
+current: ?usize = null,
+
+pub fn get_length(self: *History) u32 {
+    return @intCast(self.stack.items.len);
+}
+
+pub fn get_scrollRestoration(self: *History) ScrollRestorationMode {
+    return self.scroll_restoration;
+}
+
+pub fn set_scrollRestoration(self: *History, mode: []const u8) void {
+    self.scroll_restoration = ScrollRestorationMode.fromString(mode) orelse self.scroll_restoration;
+}
+
+pub fn get_state(self: *History, page: *Page) !?js.Value {
+    if (self.current) |curr| {
+        const entry = self.stack.items[curr];
+        if (entry.state) |state| {
+            const value = try js.Value.fromJson(page.js, state);
+            return value;
+        } else {
+            return null;
+        }
+    } else {
+        return null;
+    }
+}
+
+pub fn pushNavigation(self: *History, _url: []const u8, page: *Page) !void {
+    const arena = page.session.arena;
+    const url = try arena.dupe(u8, _url);
+
+    const entry = HistoryEntry{ .state = null, .url = url };
+    try self.stack.append(arena, entry);
+    self.current = self.stack.items.len - 1;
+}
+
+pub fn dispatchPopStateEvent(state: ?[]const u8, page: *Page) void {
+    log.debug(.script_event, "dispatch popstate event", .{
+        .type = "popstate",
+        .source = "history",
+    });
+    History._dispatchPopStateEvent(state, page) catch |err| {
+        log.err(.app, "dispatch popstate event error", .{
+            .err = err,
+            .type = "popstate",
+            .source = "history",
+        });
+    };
+}
+
+fn _dispatchPopStateEvent(state: ?[]const u8, page: *Page) !void {
+    var evt = try PopStateEvent.constructor("popstate", .{ .state = state });
+
+    _ = try parser.eventTargetDispatchEvent(
+        @as(*parser.EventTarget, @ptrCast(&page.window)),
+        &evt.proto,
+    );
+}
+
+pub fn _pushState(self: *History, state: js.Object, _: ?[]const u8, _url: ?[]const u8, page: *Page) !void {
+    const arena = page.session.arena;
+
+    const json = try state.toJson(arena);
+    const url = if (_url) |u| try arena.dupe(u8, u) else try arena.dupe(u8, page.url.raw);
+    const entry = HistoryEntry{ .state = json, .url = url };
+    try self.stack.append(arena, entry);
+    self.current = self.stack.items.len - 1;
+}
+
+pub fn _replaceState(self: *History, state: js.Object, _: ?[]const u8, _url: ?[]const u8, page: *Page) !void {
+    const arena = page.session.arena;
+
+    if (self.current) |curr| {
+        const entry = &self.stack.items[curr];
+        const json = try state.toJson(arena);
+        const url = if (_url) |u| try arena.dupe(u8, u) else try arena.dupe(u8, page.url.raw);
+        entry.* = HistoryEntry{ .state = json, .url = url };
+    } else {
+        try self._pushState(state, "", _url, page);
+    }
+}
+
+pub fn go(self: *History, delta: i32, page: *Page) !void {
+    // 0 behaves the same as no argument, both reloading the page.
+    // If this is getting called, there SHOULD be an entry, atleast from pushNavigation.
+    const current = self.current.?;
+
+    const index_s: i64 = @intCast(@as(i64, @intCast(current)) + @as(i64, @intCast(delta)));
+    if (index_s < 0 or index_s > self.stack.items.len - 1) {
+        return;
+    }
+
+    const index = @as(usize, @intCast(index_s));
+    const entry = self.stack.items[index];
+    self.current = index;
+
+    if (try page.isSameOrigin(entry.url)) {
+        History.dispatchPopStateEvent(entry.state, page);
+    }
+
+    try page.navigateFromWebAPI(entry.url, .{ .reason = .history });
+}
+
+pub fn _go(self: *History, _delta: ?i32, page: *Page) !void {
+    try self.go(_delta orelse 0, page);
+}
+
+pub fn _back(self: *History, page: *Page) !void {
+    try self.go(-1, page);
+}
+
+pub fn _forward(self: *History, page: *Page) !void {
+    try self.go(1, page);
+}
+
+const parser = @import("../netsurf.zig");
+const Event = @import("../events/event.zig").Event;
+
+pub const PopStateEvent = struct {
+    pub const prototype = *Event;
+    pub const union_make_copy = true;
+
+    pub const EventInit = struct {
+        state: ?[]const u8 = null,
+    };
+
+    proto: parser.Event,
+    state: ?[]const u8,
+
+    pub fn constructor(event_type: []const u8, opts: ?EventInit) !PopStateEvent {
+        const event = try parser.eventCreate();
+        defer parser.eventDestroy(event);
+        try parser.eventInit(event, event_type, .{});
+        parser.eventSetInternalType(event, .pop_state);
+
+        const o = opts orelse EventInit{};
+
+        return .{
+            .proto = event.*,
+            .state = o.state,
+        };
+    }
+
+    // `hasUAVisualTransition` is not implemented. It isn't baseline so this is okay.
+
+    pub fn get_state(self: *const PopStateEvent, page: *Page) !?js.Value {
+        if (self.state) |state| {
+            const value = try js.Value.fromJson(page.js, state);
+            return value;
+        } else {
+            return null;
+        }
+    }
+};
+
+const testing = @import("../../testing.zig");
+test "Browser: HTML.History" {
+    try testing.htmlRunner("html/history.html");
+}

src/browser/html/document.zig

@@ -42,12 +42,12 @@ pub const HTMLDocument = struct {
     // JS funcs
     // --------
 
-    pub fn get_domain(self: *parser.DocumentHTML, page: *Page) ![]const u8 {
+    pub fn get_domain(self: *parser.DocumentHTML) ![]const u8 {
         // libdom's document_html get_domain always returns null, this is
         // the way MDN recommends getting the domain anyways, since document.domain
         // is deprecated.
         const location = try parser.documentHTMLGetLocation(Location, self) orelse return "";
-        return location.get_host(page);
+        return location.get_host();
     }
 
     pub fn set_domain(_: *parser.DocumentHTML, _: []const u8) ![]const u8 {
@@ -115,67 +115,69 @@ pub const HTMLDocument = struct {
     }
 
     pub fn _getElementsByName(self: *parser.DocumentHTML, name: []const u8, page: *Page) !NodeList {
-        const arena = page.arena;
         var list: NodeList = .{};
 
-        if (name.len == 0) return list;
+        if (name.len == 0) {
+            return list;
+        }
 
         const root = parser.documentHTMLToNode(self);
-        var c = try collection.HTMLCollectionByName(arena, root, name, .{
+        var c = try collection.HTMLCollectionByName(root, name, .{
             .include_root = false,
         });
 
         const ln = try c.get_length();
+        try list.ensureTotalCapacity(page.arena, ln);
+
         var i: u32 = 0;
-        while (i < ln) {
+        while (i < ln) : (i += 1) {
             const n = try c.item(i) orelse break;
-            try list.append(arena, n);
-            i += 1;
+            list.appendAssumeCapacity(n);
         }
 
         return list;
     }
 
-    pub fn get_images(self: *parser.DocumentHTML, page: *Page) !collection.HTMLCollection {
-        return try collection.HTMLCollectionByTagName(page.arena, parser.documentHTMLToNode(self), "img", .{
+    pub fn get_images(self: *parser.DocumentHTML) collection.HTMLCollection {
+        return collection.HTMLCollectionByTagName(parser.documentHTMLToNode(self), "img", .{
             .include_root = false,
         });
     }
 
-    pub fn get_embeds(self: *parser.DocumentHTML, page: *Page) !collection.HTMLCollection {
-        return try collection.HTMLCollectionByTagName(page.arena, parser.documentHTMLToNode(self), "embed", .{
+    pub fn get_embeds(self: *parser.DocumentHTML) collection.HTMLCollection {
+        return collection.HTMLCollectionByTagName(parser.documentHTMLToNode(self), "embed", .{
             .include_root = false,
         });
     }
 
-    pub fn get_plugins(self: *parser.DocumentHTML, page: *Page) !collection.HTMLCollection {
-        return get_embeds(self, page);
+    pub fn get_plugins(self: *parser.DocumentHTML) collection.HTMLCollection {
+        return get_embeds(self);
     }
 
-    pub fn get_forms(self: *parser.DocumentHTML, page: *Page) !collection.HTMLCollection {
-        return try collection.HTMLCollectionByTagName(page.arena, parser.documentHTMLToNode(self), "form", .{
+    pub fn get_forms(self: *parser.DocumentHTML) collection.HTMLCollection {
+        return collection.HTMLCollectionByTagName(parser.documentHTMLToNode(self), "form", .{
             .include_root = false,
         });
     }
 
-    pub fn get_scripts(self: *parser.DocumentHTML, page: *Page) !collection.HTMLCollection {
-        return try collection.HTMLCollectionByTagName(page.arena, parser.documentHTMLToNode(self), "script", .{
+    pub fn get_scripts(self: *parser.DocumentHTML) collection.HTMLCollection {
+        return collection.HTMLCollectionByTagName(parser.documentHTMLToNode(self), "script", .{
             .include_root = false,
         });
     }
 
-    pub fn get_applets(_: *parser.DocumentHTML) !collection.HTMLCollection {
-        return try collection.HTMLCollectionEmpty();
+    pub fn get_applets(_: *parser.DocumentHTML) collection.HTMLCollection {
+        return collection.HTMLCollectionEmpty();
     }
 
-    pub fn get_links(self: *parser.DocumentHTML) !collection.HTMLCollection {
-        return try collection.HTMLCollectionByLinks(parser.documentHTMLToNode(self), .{
+    pub fn get_links(self: *parser.DocumentHTML) collection.HTMLCollection {
+        return collection.HTMLCollectionByLinks(parser.documentHTMLToNode(self), .{
             .include_root = false,
         });
     }
 
-    pub fn get_anchors(self: *parser.DocumentHTML) !collection.HTMLCollection {
-        return try collection.HTMLCollectionByAnchors(parser.documentHTMLToNode(self), .{
+    pub fn get_anchors(self: *parser.DocumentHTML) collection.HTMLCollection {
+        return collection.HTMLCollectionByAnchors(parser.documentHTMLToNode(self), .{
             .include_root = false,
         });
     }

src/browser/html/elements.zig

@@ -18,9 +18,9 @@
 const std = @import("std");
 const log = @import("../../log.zig");
 
+const js = @import("../js/js.zig");
 const parser = @import("../netsurf.zig");
-const generate = @import("../../runtime/generate.zig");
-const Env = @import("../env.zig").Env;
+const generate = @import("../js/generate.zig");
 const Page = @import("../page.zig").Page;
 
 const urlStitch = @import("../../url.zig").URL.stitch;
@@ -133,14 +133,14 @@ pub const HTMLElement = struct {
 
     pub fn get_innerText(e: *parser.ElementHTML) ![]const u8 {
         const n = @as(*parser.Node, @ptrCast(e));
-        return try parser.nodeTextContent(n) orelse "";
+        return parser.nodeTextContent(n) orelse "";
     }
 
     pub fn set_innerText(e: *parser.ElementHTML, s: []const u8) !void {
         const n = @as(*parser.Node, @ptrCast(e));
 
         // create text node.
-        const doc = try parser.nodeOwnerDocument(n) orelse return error.NoDocument;
+        const doc = parser.nodeOwnerDocument(n) orelse return error.NoDocument;
         const t = try parser.documentCreateTextNode(doc, s);
 
         // remove existing children.
@@ -167,12 +167,12 @@ pub const HTMLElement = struct {
         focusVisible: bool,
     };
     pub fn _focus(e: *parser.ElementHTML, _: ?FocusOpts, page: *Page) !void {
-        if (!try page.isNodeAttached(@ptrCast(e))) {
+        if (!page.isNodeAttached(@ptrCast(e))) {
             return;
         }
 
         const Document = @import("../dom/document.zig").Document;
-        const root_node = try parser.nodeGetRootNode(@ptrCast(e));
+        const root_node = parser.nodeGetRootNode(@ptrCast(e));
         try Document.setFocus(@ptrCast(root_node), e, page);
     }
 };
@@ -218,40 +218,40 @@ pub const HTMLAnchorElement = struct {
     }
 
     pub fn get_href(self: *parser.Anchor) ![]const u8 {
-        return try parser.anchorGetHref(self);
+        return parser.anchorGetHref(self);
     }
 
     pub fn set_href(self: *parser.Anchor, href: []const u8, page: *const Page) !void {
         const full = try urlStitch(page.call_arena, href, page.url.raw, .{});
-        return try parser.anchorSetHref(self, full);
+        return parser.anchorSetHref(self, full);
     }
 
     pub fn get_hreflang(self: *parser.Anchor) ![]const u8 {
-        return try parser.anchorGetHrefLang(self);
+        return parser.anchorGetHrefLang(self);
     }
 
     pub fn set_hreflang(self: *parser.Anchor, href: []const u8) !void {
-        return try parser.anchorSetHrefLang(self, href);
+        return parser.anchorSetHrefLang(self, href);
     }
 
     pub fn get_type(self: *parser.Anchor) ![]const u8 {
-        return try parser.anchorGetType(self);
+        return parser.anchorGetType(self);
     }
 
     pub fn set_type(self: *parser.Anchor, t: []const u8) !void {
-        return try parser.anchorSetType(self, t);
+        return parser.anchorSetType(self, t);
     }
 
     pub fn get_rel(self: *parser.Anchor) ![]const u8 {
-        return try parser.anchorGetRel(self);
+        return parser.anchorGetRel(self);
     }
 
     pub fn set_rel(self: *parser.Anchor, t: []const u8) !void {
-        return try parser.anchorSetRel(self, t);
+        return parser.anchorSetRel(self, t);
     }
 
     pub fn get_text(self: *parser.Anchor) !?[]const u8 {
-        return try parser.nodeTextContent(parser.anchorToNode(self));
+        return parser.nodeTextContent(parser.anchorToNode(self));
     }
 
     pub fn set_text(self: *parser.Anchor, v: []const u8) !void {
@@ -269,182 +269,175 @@ pub const HTMLAnchorElement = struct {
         if (try parser.elementGetAttribute(@ptrCast(@alignCast(self)), "href")) |href| {
             return URL.constructor(.{ .string = href }, null, page); // TODO inject base url
         }
-        return .empty;
+        return error.NotProvided;
     }
 
-    // TODO return a disposable string
     pub fn get_origin(self: *parser.Anchor, page: *Page) ![]const u8 {
         var u = try url(self, page);
-        return try u.get_origin(page);
+        defer u.destructor();
+        return u.get_origin(page);
     }
 
-    // TODO return a disposable string
     pub fn get_protocol(self: *parser.Anchor, page: *Page) ![]const u8 {
         var u = try url(self, page);
-        return u.get_protocol(page);
+        defer u.destructor();
+
+        return page.call_arena.dupe(u8, u.get_protocol());
     }
 
-    pub fn set_protocol(self: *parser.Anchor, v: []const u8, page: *Page) !void {
-        const arena = page.arena;
+    pub fn set_protocol(self: *parser.Anchor, protocol: []const u8, page: *Page) !void {
         var u = try url(self, page);
+        defer u.destructor();
+        try u.set_protocol(protocol);
 
-        u.uri.scheme = v;
-        const href = try u.toString(arena);
-        try parser.anchorSetHref(self, href);
+        const href = try u._toString(page);
+        return parser.anchorSetHref(self, href);
     }
 
-    // TODO return a disposable string
     pub fn get_host(self: *parser.Anchor, page: *Page) ![]const u8 {
-        var u = try url(self, page);
-        return try u.get_host(page);
+        var u = url(self, page) catch return "";
+        defer u.destructor();
+
+        return page.call_arena.dupe(u8, u.get_host());
     }
 
-    pub fn set_host(self: *parser.Anchor, v: []const u8, page: *Page) !void {
-        // search : separator
-        var p: ?u16 = null;
-        var h: []const u8 = undefined;
-        for (v, 0..) |c, i| {
-            if (c == ':') {
-                h = v[0..i];
-                p = try std.fmt.parseInt(u16, v[i + 1 ..], 10);
-                break;
-            }
-        }
-
-        const arena = page.arena;
+    pub fn set_host(self: *parser.Anchor, host: []const u8, page: *Page) !void {
         var u = try url(self, page);
+        defer u.destructor();
+        try u.set_host(host);
 
-        if (p) |pp| {
-            u.uri.host = .{ .raw = h };
-            u.uri.port = pp;
-        } else {
-            u.uri.host = .{ .raw = v };
-            u.uri.port = null;
-        }
-
-        const href = try u.toString(arena);
-        try parser.anchorSetHref(self, href);
+        const href = try u._toString(page);
+        return parser.anchorSetHref(self, href);
     }
 
     pub fn get_hostname(self: *parser.Anchor, page: *Page) ![]const u8 {
-        var u = try url(self, page);
-        return u.get_hostname();
+        var u = url(self, page) catch return "";
+        defer u.destructor();
+        return page.call_arena.dupe(u8, u.get_hostname());
     }
 
-    pub fn set_hostname(self: *parser.Anchor, v: []const u8, page: *Page) !void {
-        const arena = page.arena;
+    pub fn set_hostname(self: *parser.Anchor, hostname: []const u8, page: *Page) !void {
         var u = try url(self, page);
-        u.uri.host = .{ .raw = v };
-        const href = try u.toString(arena);
-        try parser.anchorSetHref(self, href);
+        defer u.destructor();
+        try u.set_hostname(hostname);
+
+        const href = try u._toString(page);
+        return parser.anchorSetHref(self, href);
     }
 
-    // TODO return a disposable string
     pub fn get_port(self: *parser.Anchor, page: *Page) ![]const u8 {
-        var u = try url(self, page);
-        return try u.get_port(page);
+        var u = url(self, page) catch return "";
+        defer u.destructor();
+        return page.call_arena.dupe(u8, u.get_port());
     }
 
-    pub fn set_port(self: *parser.Anchor, v: ?[]const u8, page: *Page) !void {
-        const arena = page.arena;
+    pub fn set_port(self: *parser.Anchor, maybe_port: ?[]const u8, page: *Page) !void {
         var u = try url(self, page);
+        defer u.destructor();
 
-        if (v != null and v.?.len > 0) {
-            u.uri.port = try std.fmt.parseInt(u16, v.?, 10);
+        if (maybe_port) |port| {
+            try u.set_port(port);
         } else {
-            u.uri.port = null;
+            u.clearPort();
         }
 
-        const href = try u.toString(arena);
-        try parser.anchorSetHref(self, href);
+        const href = try u._toString(page);
+        return parser.anchorSetHref(self, href);
     }
 
-    // TODO return a disposable string
     pub fn get_username(self: *parser.Anchor, page: *Page) ![]const u8 {
-        var u = try url(self, page);
-        return u.get_username();
-    }
+        var u = url(self, page) catch return "";
+        defer u.destructor();
 
-    pub fn set_username(self: *parser.Anchor, v: ?[]const u8, page: *Page) !void {
-        const arena = page.arena;
-        var u = try url(self, page);
-
-        if (v) |vv| {
-            u.uri.user = .{ .raw = vv };
-        } else {
-            u.uri.user = null;
+        const username = u.get_username();
+        if (username.len == 0) {
+            return "";
         }
-        const href = try u.toString(arena);
 
-        try parser.anchorSetHref(self, href);
+        return page.call_arena.dupe(u8, username);
+    }
+
+    pub fn set_username(self: *parser.Anchor, maybe_username: ?[]const u8, page: *Page) !void {
+        var u = try url(self, page);
+        defer u.destructor();
+
+        const username = if (maybe_username) |username| username else "";
+        try u.set_username(username);
+
+        const href = try u._toString(page);
+        return parser.anchorSetHref(self, href);
     }
 
-    // TODO return a disposable string
     pub fn get_password(self: *parser.Anchor, page: *Page) ![]const u8 {
-        var u = try url(self, page);
-        return try page.arena.dupe(u8, u.get_password());
+        var u = url(self, page) catch return "";
+        defer u.destructor();
+
+        return page.call_arena.dupe(u8, u.get_password());
     }
 
-    pub fn set_password(self: *parser.Anchor, v: ?[]const u8, page: *Page) !void {
-        const arena = page.arena;
+    pub fn set_password(self: *parser.Anchor, maybe_password: ?[]const u8, page: *Page) !void {
         var u = try url(self, page);
+        defer u.destructor();
 
-        if (v) |vv| {
-            u.uri.password = .{ .raw = vv };
-        } else {
-            u.uri.password = null;
-        }
-        const href = try u.toString(arena);
+        const password = if (maybe_password) |password| password else "";
+        try u.set_password(password);
 
-        try parser.anchorSetHref(self, href);
+        const href = try u._toString(page);
+        return parser.anchorSetHref(self, href);
     }
 
-    // TODO return a disposable string
     pub fn get_pathname(self: *parser.Anchor, page: *Page) ![]const u8 {
-        var u = try url(self, page);
-        return u.get_pathname();
+        var u = url(self, page) catch return "";
+        defer u.destructor();
+
+        return page.call_arena.dupe(u8, u.get_pathname());
     }
 
-    pub fn set_pathname(self: *parser.Anchor, v: []const u8, page: *Page) !void {
-        const arena = page.arena;
+    pub fn set_pathname(self: *parser.Anchor, pathname: []const u8, page: *Page) !void {
         var u = try url(self, page);
-        u.uri.path = .{ .raw = v };
-        const href = try u.toString(arena);
+        defer u.destructor();
 
-        try parser.anchorSetHref(self, href);
+        try u.set_pathname(pathname);
+
+        const href = try u._toString(page);
+        return parser.anchorSetHref(self, href);
     }
 
     pub fn get_search(self: *parser.Anchor, page: *Page) ![]const u8 {
-        var u = try url(self, page);
-        return try u.get_search(page);
+        var u = url(self, page) catch return "";
+        defer u.destructor();
+        // This allocates in page arena so no need to dupe.
+        return u.get_search(page);
     }
 
     pub fn set_search(self: *parser.Anchor, v: ?[]const u8, page: *Page) !void {
         var u = try url(self, page);
+        defer u.destructor();
         try u.set_search(v, page);
 
-        const href = try u.toString(page.call_arena);
-        try parser.anchorSetHref(self, href);
+        const href = try u._toString(page);
+        return parser.anchorSetHref(self, href);
     }
 
-    // TODO return a disposable string
     pub fn get_hash(self: *parser.Anchor, page: *Page) ![]const u8 {
-        var u = try url(self, page);
-        return try u.get_hash(page);
+        var u = url(self, page) catch return "";
+        defer u.destructor();
+
+        return page.call_arena.dupe(u8, u.get_hash());
     }
 
-    pub fn set_hash(self: *parser.Anchor, v: ?[]const u8, page: *Page) !void {
-        const arena = page.arena;
+    pub fn set_hash(self: *parser.Anchor, maybe_hash: ?[]const u8, page: *Page) !void {
         var u = try url(self, page);
+        defer u.destructor();
 
-        if (v) |vv| {
-            u.uri.fragment = .{ .raw = vv };
+        if (maybe_hash) |hash| {
+            try u.set_hash(hash);
         } else {
-            u.uri.fragment = null;
+            u.clearHash();
         }
-        const href = try u.toString(arena);
 
-        try parser.anchorSetHref(self, href);
+        const href = try u._toString(page);
+        return parser.anchorSetHref(self, href);
     }
 };
 
@@ -732,6 +725,9 @@ pub const HTMLInputElement = struct {
     pub fn set_value(self: *parser.Input, value: []const u8) !void {
         try parser.inputSetValue(self, value);
     }
+    pub fn _select(_: *parser.Input) void {
+        log.debug(.web_api, "not implemented", .{ .feature = "HTMLInputElement select" });
+    }
 };
 
 pub const HTMLLIElement = struct {
@@ -757,13 +753,21 @@ pub const HTMLLinkElement = struct {
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
 
+    pub fn get_rel(self: *parser.Link) ![]const u8 {
+        return parser.linkGetRel(self);
+    }
+
+    pub fn set_rel(self: *parser.Link, rel: []const u8) !void {
+        return parser.linkSetRel(self, rel);
+    }
+
     pub fn get_href(self: *parser.Link) ![]const u8 {
-        return try parser.linkGetHref(self);
+        return parser.linkGetHref(self);
     }
 
     pub fn set_href(self: *parser.Link, href: []const u8, page: *const Page) !void {
         const full = try urlStitch(page.call_arena, href, page.url.raw, .{});
-        return try parser.linkSetHref(self, full);
+        return parser.linkSetHref(self, full);
     }
 };
 
@@ -879,7 +883,7 @@ pub const HTMLScriptElement = struct {
             //    s.src = '...';
             // This should load the script.
             // addFromElement protects against double execution.
-            try page.script_manager.addFromElement(@ptrCast(@alignCast(self)));
+            try page.script_manager.addFromElement(@ptrCast(@alignCast(self)), "dynamic");
         }
     }
 
@@ -992,22 +996,22 @@ pub const HTMLScriptElement = struct {
         );
     }
 
-    pub fn get_onload(self: *parser.Script, page: *Page) !?Env.Function {
+    pub fn get_onload(self: *parser.Script, page: *Page) !?js.Function {
         const state = page.getNodeState(@ptrCast(@alignCast(self))) orelse return null;
         return state.onload;
     }
 
-    pub fn set_onload(self: *parser.Script, function: ?Env.Function, page: *Page) !void {
+    pub fn set_onload(self: *parser.Script, function: ?js.Function, page: *Page) !void {
         const state = try page.getOrCreateNodeState(@ptrCast(@alignCast(self)));
         state.onload = function;
     }
 
-    pub fn get_onerror(self: *parser.Script, page: *Page) !?Env.Function {
+    pub fn get_onerror(self: *parser.Script, page: *Page) !?js.Function {
         const state = page.getNodeState(@ptrCast(@alignCast(self))) orelse return null;
         return state.onerror;
     }
 
-    pub fn set_onerror(self: *parser.Script, function: ?Env.Function, page: *Page) !void {
+    pub fn set_onerror(self: *parser.Script, function: ?js.Function, page: *Page) !void {
         const state = try page.getOrCreateNodeState(@ptrCast(@alignCast(self)));
         state.onerror = function;
     }
@@ -1064,7 +1068,7 @@ pub const HTMLSlotElement = struct {
         // First we look for any explicitly assigned nodes (via the slot attribute)
         {
             const slot_name = try parser.elementGetAttribute(@ptrCast(@alignCast(self)), "name");
-            var root = try parser.nodeGetRootNode(node);
+            var root = parser.nodeGetRootNode(node);
             if (page.getNodeState(root)) |state| {
                 if (state.shadow_root) |sr| {
                     root = @ptrCast(@alignCast(sr.host));
@@ -1076,7 +1080,7 @@ pub const HTMLSlotElement = struct {
             var next: ?*parser.Node = null;
             while (true) {
                 next = try w.get_next(root, next) orelse break;
-                if (try parser.nodeType(next.?) != .element) {
+                if (parser.nodeType(next.?) != .element) {
                     if (slot_name == null and !element_only) {
                         // default slot (with no name), takes everything
                         try arr.append(page.call_arena, try Node.toInterface(next.?));
@@ -1105,7 +1109,7 @@ pub const HTMLSlotElement = struct {
         // we'll collect the children of the slot - the defaults.
         {
             const nl = try parser.nodeGetChildNodes(node);
-            const len = try parser.nodeListLength(nl);
+            const len = parser.nodeListLength(nl);
             if (len == 0) {
                 return &.{};
             }
@@ -1113,8 +1117,8 @@ pub const HTMLSlotElement = struct {
             var assigned = try page.call_arena.alloc(NodeUnion, len);
             var i: usize = 0;
             while (true) : (i += 1) {
-                const child = try parser.nodeListItem(nl, @intCast(i)) orelse break;
-                if (!element_only or try parser.nodeType(child) == .element) {
+                const child = parser.nodeListItem(nl, @intCast(i)) orelse break;
+                if (!element_only or parser.nodeType(child) == .element) {
                     assigned[i] = try Node.toInterface(child);
                 }
             }
@@ -1343,6 +1347,9 @@ test "Browser: HTML.HtmlStyleElement" {
 test "Browser: HTML.HtmlScriptElement" {
     try testing.htmlRunner("html/script/script.html");
     try testing.htmlRunner("html/script/inline_defer.html");
+    try testing.htmlRunner("html/script/import.html");
+    try testing.htmlRunner("html/script/dynamic_import.html");
+    try testing.htmlRunner("html/script/importmap.html");
 }
 
 test "Browser: HTML.HtmlSlotElement" {

src/browser/html/error_event.zig

@@ -15,7 +15,7 @@
 //
 // You should have received a copy of the GNU Affero General Public License
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.
-const Env = @import("../env.zig").Env;
+const js = @import("../js/js.zig");
 const parser = @import("../netsurf.zig");
 
 // https://developer.mozilla.org/en-US/docs/Web/API/ErrorEvent
@@ -28,21 +28,21 @@ pub const ErrorEvent = struct {
     filename: []const u8,
     lineno: i32,
     colno: i32,
-    @"error": ?Env.JsObject,
+    @"error": ?js.Object,
 
     const ErrorEventInit = struct {
         message: []const u8 = "",
         filename: []const u8 = "",
         lineno: i32 = 0,
         colno: i32 = 0,
-        @"error": ?Env.JsObject = null,
+        @"error": ?js.Object = null,
     };
 
     pub fn constructor(event_type: []const u8, opts: ?ErrorEventInit) !ErrorEvent {
         const event = try parser.eventCreate();
         defer parser.eventDestroy(event);
         try parser.eventInit(event, event_type, .{});
-        parser.eventSetInternalType(event, .event);
+        parser.eventSetInternalType(event, .error_event);
 
         const o = opts orelse ErrorEventInit{};
 
@@ -72,7 +72,7 @@ pub const ErrorEvent = struct {
         return self.colno;
     }
 
-    pub fn get_error(self: *const ErrorEvent) Env.UndefinedOr(Env.JsObject) {
+    pub fn get_error(self: *const ErrorEvent) js.UndefinedOr(js.Object) {
         if (self.@"error") |e| {
             return .{ .value = e };
         }

src/browser/html/form.zig

@@ -21,7 +21,6 @@ const Allocator = std.mem.Allocator;
 const parser = @import("../netsurf.zig");
 const Page = @import("../page.zig").Page;
 const HTMLElement = @import("elements.zig").HTMLElement;
-const FormData = @import("../xhr/form_data.zig").FormData;
 
 pub const HTMLFormElement = struct {
     pub const Self = parser.Form;

src/browser/html/history.zig

@@ -1,93 +0,0 @@
-// Copyright (C) 2023-2024  Lightpanda (Selecy SAS)
-//
-// Francis Bouvier <francis@lightpanda.io>
-// Pierre Tachoire <pierre@lightpanda.io>
-//
-// This program is free software: you can redistribute it and/or modify
-// it under the terms of the GNU Affero General Public License as
-// published by the Free Software Foundation, either version 3 of the
-// License, or (at your option) any later version.
-//
-// This program is distributed in the hope that it will be useful,
-// but WITHOUT ANY WARRANTY; without even the implied warranty of
-// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-// GNU Affero General Public License for more details.
-//
-// You should have received a copy of the GNU Affero General Public License
-// along with this program.  If not, see <https://www.gnu.org/licenses/>.
-
-const std = @import("std");
-
-// https://html.spec.whatwg.org/multipage/nav-history-apis.html#the-history-interface
-pub const History = struct {
-    const ScrollRestorationMode = enum {
-        auto,
-        manual,
-    };
-
-    scrollRestoration: ScrollRestorationMode = .auto,
-    state: std.json.Value = .null,
-
-    // count tracks the history length until we implement correctly pushstate.
-    count: u32 = 0,
-
-    pub fn get_length(self: *History) u32 {
-        // TODO return the real history length value.
-        return self.count;
-    }
-
-    pub fn get_scrollRestoration(self: *History) []const u8 {
-        return switch (self.scrollRestoration) {
-            .auto => "auto",
-            .manual => "manual",
-        };
-    }
-
-    pub fn set_scrollRestoration(self: *History, mode: []const u8) void {
-        if (std.mem.eql(u8, "manual", mode)) self.scrollRestoration = .manual;
-        if (std.mem.eql(u8, "auto", mode)) self.scrollRestoration = .auto;
-    }
-
-    pub fn get_state(self: *History) std.json.Value {
-        return self.state;
-    }
-
-    // TODO implement the function
-    // data must handle any argument. We could expect a std.json.Value but
-    // https://github.com/lightpanda-io/zig-js-runtime/issues/267 is missing.
-    pub fn _pushState(self: *History, data: []const u8, _: ?[]const u8, url: ?[]const u8) void {
-        self.count += 1;
-        _ = url;
-        _ = data;
-    }
-
-    // TODO implement the function
-    // data must handle any argument. We could expect a std.json.Value but
-    // https://github.com/lightpanda-io/zig-js-runtime/issues/267 is missing.
-    pub fn _replaceState(self: *History, data: []const u8, _: ?[]const u8, url: ?[]const u8) void {
-        _ = self;
-        _ = url;
-        _ = data;
-    }
-
-    // TODO implement the function
-    pub fn _go(self: *History, delta: ?i32) void {
-        _ = self;
-        _ = delta;
-    }
-
-    // TODO implement the function
-    pub fn _back(self: *History) void {
-        _ = self;
-    }
-
-    // TODO implement the function
-    pub fn _forward(self: *History) void {
-        _ = self;
-    }
-};
-
-const testing = @import("../../testing.zig");
-test "Browser: HTML.History" {
-    try testing.htmlRunner("html/history.html");
-}

src/browser/html/html.zig

@@ -21,7 +21,7 @@ const HTMLElem = @import("elements.zig");
 const SVGElem = @import("svg_elements.zig");
 const Window = @import("window.zig").Window;
 const Navigator = @import("navigator.zig").Navigator;
-const History = @import("history.zig").History;
+const History = @import("History.zig");
 const Location = @import("location.zig").Location;
 const MediaQueryList = @import("media_query_list.zig").MediaQueryList;
 

src/browser/html/iframe.zig

@@ -16,10 +16,8 @@
 // You should have received a copy of the GNU Affero General Public License
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.
 const std = @import("std");
-const Allocator = std.mem.Allocator;
 
 const parser = @import("../netsurf.zig");
-const Page = @import("../page.zig").Page;
 const HTMLElement = @import("elements.zig").HTMLElement;
 
 // https://html.spec.whatwg.org/multipage/iframe-embed-object.html#htmliframeelement

src/browser/html/location.zig

@@ -16,57 +16,62 @@
 // You should have received a copy of the GNU Affero General Public License
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
-const Page = @import("../page.zig").Page;
+const Uri = @import("std").Uri;
 
+const Page = @import("../page.zig").Page;
 const URL = @import("../url/url.zig").URL;
 
 // https://html.spec.whatwg.org/multipage/nav-history-apis.html#the-location-interface
 pub const Location = struct {
-    url: ?URL = null,
+    url: URL,
+
+    /// Initializes the `Location` to be used in `Window`.
+    /// Browsers give such initial values when user not navigated yet:
+    /// Chrome  -> chrome://new-tab-page/
+    /// Firefox -> about:newtab
+    /// Safari  -> favorites://
+    pub fn init(url: []const u8) !Location {
+        return .{ .url = try .initForLocation(url) };
+    }
 
     pub fn get_href(self: *Location, page: *Page) ![]const u8 {
-        if (self.url) |*u| return u.get_href(page);
-        return "";
+        return self.url.get_href(page);
     }
 
-    pub fn get_protocol(self: *Location, page: *Page) ![]const u8 {
-        if (self.url) |*u| return u.get_protocol(page);
-        return "";
+    pub fn set_href(_: *const Location, href: []const u8, page: *Page) !void {
+        return page.navigateFromWebAPI(href, .{ .reason = .script });
     }
 
-    pub fn get_host(self: *Location, page: *Page) ![]const u8 {
-        if (self.url) |*u| return u.get_host(page);
-        return "";
+    pub fn get_protocol(self: *Location) []const u8 {
+        return self.url.get_protocol();
+    }
+
+    pub fn get_host(self: *Location) []const u8 {
+        return self.url.get_host();
     }
 
     pub fn get_hostname(self: *Location) []const u8 {
-        if (self.url) |*u| return u.get_hostname();
-        return "";
+        return self.url.get_hostname();
     }
 
-    pub fn get_port(self: *Location, page: *Page) ![]const u8 {
-        if (self.url) |*u| return u.get_port(page);
-        return "";
+    pub fn get_port(self: *Location) []const u8 {
+        return self.url.get_port();
     }
 
     pub fn get_pathname(self: *Location) []const u8 {
-        if (self.url) |*u| return u.get_pathname();
-        return "";
+        return self.url.get_pathname();
     }
 
     pub fn get_search(self: *Location, page: *Page) ![]const u8 {
-        if (self.url) |*u| return u.get_search(page);
-        return "";
+        return self.url.get_search(page);
     }
 
-    pub fn get_hash(self: *Location, page: *Page) ![]const u8 {
-        if (self.url) |*u| return u.get_hash(page);
-        return "";
+    pub fn get_hash(self: *Location) []const u8 {
+        return self.url.get_hash();
     }
 
     pub fn get_origin(self: *Location, page: *Page) ![]const u8 {
-        if (self.url) |*u| return u.get_origin(page);
-        return "";
+        return self.url.get_origin(page);
     }
 
     pub fn _assign(_: *const Location, url: []const u8, page: *Page) !void {
@@ -82,7 +87,7 @@ pub const Location = struct {
     }
 
     pub fn _toString(self: *Location, page: *Page) ![]const u8 {
-        return try self.get_href(page);
+        return self.get_href(page);
     }
 };
 

src/browser/html/media_query_list.zig

@@ -16,8 +16,8 @@
 // You should have received a copy of the GNU Affero General Public License
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
+const js = @import("../js/js.zig");
 const parser = @import("../netsurf.zig");
-const Function = @import("../env.zig").Function;
 const EventTarget = @import("../dom/event_target.zig").EventTarget;
 
 // https://drafts.csswg.org/cssom-view/#the-mediaquerylist-interface
@@ -39,7 +39,7 @@ pub const MediaQueryList = struct {
         return self.media;
     }
 
-    pub fn _addListener(_: *const MediaQueryList, _: Function) void {}
+    pub fn _addListener(_: *const MediaQueryList, _: js.Function) void {}
 
-    pub fn _removeListener(_: *const MediaQueryList, _: Function) void {}
+    pub fn _removeListener(_: *const MediaQueryList, _: js.Function) void {}
 };

src/browser/html/svg_elements.zig

@@ -25,7 +25,7 @@ pub const SVGElement = struct {
     // Currently the prototype chain is not implemented (will not be returned by toInterface())
     // For that we need parser.SvgElement and the derived types with tags in the v-table.
     pub const prototype = *Element;
-    // While this is a Node, could consider not exposing the subtype untill we have
+    // While this is a Node, could consider not exposing the subtype until we have
     // a Self type to cast to.
     pub const subtype = .node;
 };

src/browser/html/window.zig

@@ -18,13 +18,13 @@
 
 const std = @import("std");
 
+const js = @import("../js/js.zig");
 const log = @import("../../log.zig");
 const parser = @import("../netsurf.zig");
-const Env = @import("../env.zig").Env;
 const Page = @import("../page.zig").Page;
 
 const Navigator = @import("navigator.zig").Navigator;
-const History = @import("history.zig").History;
+const History = @import("History.zig");
 const Location = @import("location.zig").Location;
 const Crypto = @import("../crypto/crypto.zig").Crypto;
 const Console = @import("../console/console.zig").Console;
@@ -35,11 +35,13 @@ const CSSStyleDeclaration = @import("../cssom/CSSStyleDeclaration.zig");
 const Screen = @import("screen.zig").Screen;
 const domcss = @import("../dom/css.zig");
 const Css = @import("../css/css.zig").Css;
+const EventHandler = @import("../events/event.zig").EventHandler;
 
-const Function = Env.Function;
-const JsObject = Env.JsObject;
+const Request = @import("../fetch/Request.zig");
+const fetchFn = @import("../fetch/fetch.zig").fetch;
 
 const storage = @import("../storage/storage.zig");
+const ErrorEvent = @import("error_event.zig").ErrorEvent;
 
 // https://dom.spec.whatwg.org/#interface-window-extensions
 // https://html.spec.whatwg.org/multipage/nav-history-apis.html#window
@@ -51,8 +53,7 @@ pub const Window = struct {
 
     document: *parser.DocumentHTML,
     target: []const u8 = "",
-    history: History = .{},
-    location: Location = .{},
+    location: Location,
     storage_shelf: ?*storage.Shelf = null,
 
     // counter for having unique timer ids
@@ -65,6 +66,9 @@ pub const Window = struct {
     performance: Performance,
     screen: Screen = .{},
     css: Css = .{},
+    scroll_x: u32 = 0,
+    scroll_y: u32 = 0,
+    onload_callback: ?js.Function = null,
 
     pub fn create(target: ?[]const u8, navigator: ?Navigator) !Window {
         var fbs = std.io.fixedBufferStream("");
@@ -75,6 +79,7 @@ pub const Window = struct {
         return .{
             .document = html_doc,
             .target = target orelse "",
+            .location = try .init("about:blank"),
             .navigator = navigator orelse .{},
             .performance = Performance.init(),
         };
@@ -85,6 +90,10 @@ pub const Window = struct {
         try parser.documentHTMLSetLocation(Location, self.document, &self.location);
     }
 
+    pub fn changeLocation(self: *Window, new_url: []const u8, page: *Page) !void {
+        return self.location.url.reinit(new_url, page);
+    }
+
     pub fn replaceDocument(self: *Window, doc: *parser.DocumentHTML) !void {
         self.performance.reset(); // When to reset see: https://developer.mozilla.org/en-US/docs/Web/API/Performance/timeOrigin
         self.document = doc;
@@ -95,12 +104,42 @@ pub const Window = struct {
         self.storage_shelf = shelf;
     }
 
-    pub fn get_window(self: *Window) *Window {
-        return self;
+    pub fn _fetch(_: *Window, input: Request.RequestInput, options: ?Request.RequestInit, page: *Page) !js.Promise {
+        return fetchFn(input, options, page);
     }
 
-    pub fn get_navigator(self: *Window) *Navigator {
-        return &self.navigator;
+    /// Returns `onload_callback`.
+    pub fn get_onload(self: *const Window) ?js.Function {
+        return self.onload_callback;
+    }
+
+    /// Sets `onload_callback`.
+    pub fn set_onload(self: *Window, maybe_listener: ?EventHandler.Listener, page: *Page) !void {
+        const event_target = parser.toEventTarget(Window, self);
+        const event_type = "load";
+
+        // Check if we have a listener set.
+        if (self.onload_callback) |callback| {
+            const listener = try parser.eventTargetHasListener(event_target, event_type, false, callback.id);
+            std.debug.assert(listener != null);
+            try parser.eventTargetRemoveEventListener(event_target, event_type, listener.?, false);
+        }
+
+        if (maybe_listener) |listener| {
+            switch (listener) {
+                // If an object is given as listener, do nothing.
+                .object => {},
+                .function => |callback| {
+                    _ = try EventHandler.register(page.arena, event_target, event_type, listener, null) orelse unreachable;
+                    self.onload_callback = callback;
+
+                    return;
+                },
+            }
+        }
+
+        // Just unset the listener.
+        self.onload_callback = null;
     }
 
     pub fn get_location(self: *Window) *Location {
@@ -111,22 +150,6 @@ pub const Window = struct {
         return page.navigateFromWebAPI(url, .{ .reason = .script });
     }
 
-    pub fn get_console(self: *Window) *Console {
-        return &self.console;
-    }
-
-    pub fn get_crypto(self: *Window) *Crypto {
-        return &self.crypto;
-    }
-
-    pub fn get_self(self: *Window) *Window {
-        return self;
-    }
-
-    pub fn get_parent(self: *Window) *Window {
-        return self;
-    }
-
     // frames return the window itself, but accessing it via a pseudo
     // array returns the Window object corresponding to the given frame or
     // iframe.
@@ -164,16 +187,12 @@ pub const Window = struct {
         return frames.get_length();
     }
 
-    pub fn get_top(self: *Window) *Window {
-        return self;
-    }
-
     pub fn get_document(self: *Window) ?*parser.DocumentHTML {
         return self.document;
     }
 
-    pub fn get_history(self: *Window) *History {
-        return &self.history;
+    pub fn get_history(_: *Window, page: *Page) *History {
+        return &page.session.history;
     }
 
     //  The interior height of the window in pixels, including the height of the horizontal scroll bar, if present.
@@ -202,19 +221,11 @@ pub const Window = struct {
         return &self.storage_shelf.?.bucket.session;
     }
 
-    pub fn get_performance(self: *Window) *Performance {
-        return &self.performance;
-    }
-
-    pub fn get_screen(self: *Window) *Screen {
-        return &self.screen;
-    }
-
     pub fn get_CSS(self: *Window) *Css {
         return &self.css;
     }
 
-    pub fn _requestAnimationFrame(self: *Window, cbk: Function, page: *Page) !u32 {
+    pub fn _requestAnimationFrame(self: *Window, cbk: js.Function, page: *Page) !u32 {
         return self.createTimeout(cbk, 5, page, .{
             .animation_frame = true,
             .name = "animationFrame",
@@ -226,11 +237,11 @@ pub const Window = struct {
         _ = self.timers.remove(id);
     }
 
-    pub fn _setTimeout(self: *Window, cbk: Function, delay: ?u32, params: []Env.JsObject, page: *Page) !u32 {
+    pub fn _setTimeout(self: *Window, cbk: js.Function, delay: ?u32, params: []js.Object, page: *Page) !u32 {
         return self.createTimeout(cbk, delay, page, .{ .args = params, .name = "setTimeout" });
     }
 
-    pub fn _setInterval(self: *Window, cbk: Function, delay: ?u32, params: []Env.JsObject, page: *Page) !u32 {
+    pub fn _setInterval(self: *Window, cbk: js.Function, delay: ?u32, params: []js.Object, page: *Page) !u32 {
         return self.createTimeout(cbk, delay, page, .{ .repeat = true, .args = params, .name = "setInterval" });
     }
 
@@ -242,14 +253,22 @@ pub const Window = struct {
         _ = self.timers.remove(id);
     }
 
-    pub fn _queueMicrotask(self: *Window, cbk: Function, page: *Page) !u32 {
+    pub fn _queueMicrotask(self: *Window, cbk: js.Function, page: *Page) !u32 {
         return self.createTimeout(cbk, 0, page, .{ .name = "queueMicrotask" });
     }
 
-    pub fn _matchMedia(_: *const Window, media: []const u8, page: *Page) !MediaQueryList {
+    pub fn _setImmediate(self: *Window, cbk: js.Function, page: *Page) !u32 {
+        return self.createTimeout(cbk, 0, page, .{ .name = "setImmediate" });
+    }
+
+    pub fn _clearImmediate(self: *Window, id: u32) void {
+        _ = self.timers.remove(id);
+    }
+
+    pub fn _matchMedia(_: *const Window, media: js.String) !MediaQueryList {
         return .{
             .matches = false, // TODO?
-            .media = try page.arena.dupe(u8, media),
+            .media = media.string,
         };
     }
 
@@ -268,14 +287,33 @@ pub const Window = struct {
         return out;
     }
 
+    pub fn _reportError(self: *Window, err: js.Object, page: *Page) !void {
+        var error_event = try ErrorEvent.constructor("error", .{
+            .@"error" = err,
+        });
+        _ = try parser.eventTargetDispatchEvent(
+            parser.toEventTarget(Window, self),
+            @as(*parser.Event, &error_event.proto),
+        );
+
+        if (parser.eventDefaultPrevented(&error_event.proto) == false) {
+            const err_string = err.toString() catch "Unknown error";
+            log.info(.user_script, "error", .{
+                .err = err_string,
+                .stack = page.stackTrace() catch "???",
+                .source = "window.reportError",
+            });
+        }
+    }
+
     const CreateTimeoutOpts = struct {
         name: []const u8,
-        args: []Env.JsObject = &.{},
+        args: []js.Object = &.{},
         repeat: bool = false,
         animation_frame: bool = false,
         low_priority: bool = false,
     };
-    fn createTimeout(self: *Window, cbk: Function, delay_: ?u32, page: *Page, opts: CreateTimeoutOpts) !u32 {
+    fn createTimeout(self: *Window, cbk: js.Function, delay_: ?u32, page: *Page, opts: CreateTimeoutOpts) !u32 {
         const delay = delay_ orelse 0;
         if (self.timers.count() > 512) {
             return error.TooManyTimeout;
@@ -295,9 +333,9 @@ pub const Window = struct {
         errdefer _ = self.timers.remove(timer_id);
 
         const args = opts.args;
-        var persisted_args: []Env.JsObject = &.{};
+        var persisted_args: []js.Object = &.{};
         if (args.len > 0) {
-            persisted_args = try page.arena.alloc(Env.JsObject, args.len);
+            persisted_args = try page.arena.alloc(js.Object, args.len);
             for (args, persisted_args) |a, *ca| {
                 ca.* = try a.persist();
             }
@@ -338,12 +376,20 @@ pub const Window = struct {
         const Opts = struct {
             top: i32,
             left: i32,
-            behavior: []const u8,
+            behavior: []const u8 = "",
         };
     };
-    pub fn _scrollTo(self: *Window, opts: ScrollToOpts, y: ?u32) !void {
-        _ = opts;
-        _ = y;
+    pub fn _scrollTo(self: *Window, opts: ScrollToOpts, y: ?i32) !void {
+        switch (opts) {
+            .x => |x| {
+                self.scroll_x = @intCast(@max(x, 0));
+                self.scroll_y = @intCast(@max(0, y orelse 0));
+            },
+            .opts => |o| {
+                self.scroll_y = @intCast(@max(0, o.top));
+                self.scroll_x = @intCast(@max(0, o.left));
+            },
+        }
 
         {
             const scroll_event = try parser.eventCreate();
@@ -367,6 +413,28 @@ pub const Window = struct {
             );
         }
     }
+    pub fn _scroll(self: *Window, opts: ScrollToOpts, y: ?i32) !void {
+        // just an alias for scrollTo
+        return self._scrollTo(opts, y);
+    }
+
+    pub fn get_scrollX(self: *const Window) u32 {
+        return self.scroll_x;
+    }
+
+    pub fn get_scrollY(self: *const Window) u32 {
+        return self.scroll_y;
+    }
+
+    pub fn get_pageXOffset(self: *const Window) u32 {
+        // just an alias for scrollX
+        return self.get_scrollX();
+    }
+
+    pub fn get_pageYOffset(self: *const Window) u32 {
+        // just an alias for scrollY
+        return self.get_scrollY();
+    }
 
     // libdom's document doesn't have a parent, which is correct, but
     // breaks the event bubbling that happens for many events from
@@ -384,6 +452,18 @@ pub const Window = struct {
         // and thus the target has already been set to the document.
         return self.base.redispatchEvent(evt);
     }
+
+    pub fn postAttach(self: *Window, js_this: js.This) !void {
+        try js_this.set("top", self, .{});
+        try js_this.set("self", self, .{});
+        try js_this.set("parent", self, .{});
+        try js_this.set("window", self, .{});
+        try js_this.set("crypto", &self.crypto, .{});
+        try js_this.set("screen", &self.screen, .{});
+        try js_this.set("console", &self.console, .{});
+        try js_this.set("navigator", &self.navigator, .{});
+        try js_this.set("performance", &self.performance, .{});
+    }
 };
 
 const TimerCallback = struct {
@@ -394,13 +474,13 @@ const TimerCallback = struct {
     repeat: ?u32,
 
     // The JavaScript callback to execute
-    cbk: Function,
+    cbk: js.Function,
 
     animation_frame: bool = false,
 
     window: *Window,
 
-    args: []Env.JsObject = &.{},
+    args: []js.Object = &.{},
 
     fn run(ctx: *anyopaque) ?u32 {
         const self: *TimerCallback = @ptrCast(@alignCast(ctx));
@@ -414,7 +494,7 @@ const TimerCallback = struct {
             return null;
         }
 
-        var result: Function.Result = undefined;
+        var result: js.Function.Result = undefined;
 
         var call: anyerror!void = undefined;
         if (self.animation_frame) {

src/browser/js/Caller.zig

@@ -0,0 +1,561 @@
+const std = @import("std");
+const js = @import("js.zig");
+const v8 = js.v8;
+
+const log = @import("../../log.zig");
+const Page = @import("../page.zig").Page;
+
+const types = @import("types.zig");
+const Context = @import("Context.zig");
+
+const Allocator = std.mem.Allocator;
+const ArenaAllocator = std.heap.ArenaAllocator;
+
+const CALL_ARENA_RETAIN = 1024 * 16;
+
+// Responsible for calling Zig functions from JS invocations. This could
+// probably just contained in ExecutionWorld, but having this specific logic, which
+// is somewhat repetitive between constructors, functions, getters, etc contained
+// here does feel like it makes it cleaner.
+const Caller = @This();
+context: *Context,
+v8_context: v8.Context,
+isolate: v8.Isolate,
+call_arena: Allocator,
+
+// info is a v8.PropertyCallbackInfo or a v8.FunctionCallback
+// All we really want from it is the isolate.
+// executor = Isolate -> getCurrentContext -> getEmbedderData()
+pub fn init(info: anytype) Caller {
+    const isolate = info.getIsolate();
+    const v8_context = isolate.getCurrentContext();
+    const context: *Context = @ptrFromInt(v8_context.getEmbedderData(1).castTo(v8.BigInt).getUint64());
+
+    context.call_depth += 1;
+    return .{
+        .context = context,
+        .isolate = isolate,
+        .v8_context = v8_context,
+        .call_arena = context.call_arena,
+    };
+}
+
+pub fn deinit(self: *Caller) void {
+    const context = self.context;
+    const call_depth = context.call_depth - 1;
+
+    // Because of callbacks, calls can be nested. Because of this, we
+    // can't clear the call_arena after _every_ call. Imagine we have
+    //    arr.forEach((i) => { console.log(i); }
+    //
+    // First we call forEach. Inside of our forEach call,
+    // we call console.log. If we reset the call_arena after this call,
+    // it'll reset it for the `forEach` call after, which might still
+    // need the data.
+    //
+    // Therefore, we keep a call_depth, and only reset the call_arena
+    // when a top-level (call_depth == 0) function ends.
+    if (call_depth == 0) {
+        const arena: *ArenaAllocator = @ptrCast(@alignCast(context.call_arena.ptr));
+        _ = arena.reset(.{ .retain_with_limit = CALL_ARENA_RETAIN });
+    }
+
+    // Set this _after_ we've executed the above code, so that if the
+    // above code executes any callbacks, they aren't being executed
+    // at scope 0, which would be wrong.
+    context.call_depth = call_depth;
+}
+
+pub fn constructor(self: *Caller, comptime Struct: type, comptime named_function: NamedFunction, info: v8.FunctionCallbackInfo) !void {
+    const args = try self.getArgs(Struct, named_function, 0, info);
+    const res = @call(.auto, Struct.constructor, args);
+
+    const ReturnType = @typeInfo(@TypeOf(Struct.constructor)).@"fn".return_type orelse {
+        @compileError(@typeName(Struct) ++ " has a constructor without a return type");
+    };
+
+    const this = info.getThis();
+    if (@typeInfo(ReturnType) == .error_union) {
+        const non_error_res = res catch |err| return err;
+        _ = try self.context.mapZigInstanceToJs(this, non_error_res);
+    } else {
+        _ = try self.context.mapZigInstanceToJs(this, res);
+    }
+    info.getReturnValue().set(this);
+}
+
+pub fn method(self: *Caller, comptime Struct: type, comptime named_function: NamedFunction, info: v8.FunctionCallbackInfo) !void {
+    if (comptime isSelfReceiver(Struct, named_function) == false) {
+        return self.function(Struct, named_function, info);
+    }
+
+    const context = self.context;
+    const func = @field(Struct, named_function.name);
+    var args = try self.getArgs(Struct, named_function, 1, info);
+    const zig_instance = try context.typeTaggedAnyOpaque(named_function, *types.Receiver(Struct), info.getThis());
+
+    // inject 'self' as the first parameter
+    @field(args, "0") = zig_instance;
+
+    const res = @call(.auto, func, args);
+    info.getReturnValue().set(try context.zigValueToJs(res));
+}
+
+pub fn function(self: *Caller, comptime Struct: type, comptime named_function: NamedFunction, info: v8.FunctionCallbackInfo) !void {
+    const context = self.context;
+    const func = @field(Struct, named_function.name);
+    const args = try self.getArgs(Struct, named_function, 0, info);
+    const res = @call(.auto, func, args);
+    info.getReturnValue().set(try context.zigValueToJs(res));
+}
+
+pub fn getIndex(self: *Caller, comptime Struct: type, comptime named_function: NamedFunction, idx: u32, info: v8.PropertyCallbackInfo) !u8 {
+    const context = self.context;
+    const func = @field(Struct, named_function.name);
+    const IndexedGet = @TypeOf(func);
+    if (@typeInfo(IndexedGet).@"fn".return_type == null) {
+        @compileError(named_function.full_name ++ " must have a return type");
+    }
+
+    var has_value = true;
+
+    var args: ParamterTypes(IndexedGet) = undefined;
+    const arg_fields = @typeInfo(@TypeOf(args)).@"struct".fields;
+    switch (arg_fields.len) {
+        0, 1, 2 => @compileError(named_function.full_name ++ " must take at least a u32 and *bool parameter"),
+        3, 4 => {
+            const zig_instance = try context.typeTaggedAnyOpaque(named_function, *types.Receiver(Struct), info.getThis());
+            comptime assertSelfReceiver(Struct, named_function);
+            @field(args, "0") = zig_instance;
+            @field(args, "1") = idx;
+            @field(args, "2") = &has_value;
+            if (comptime arg_fields.len == 4) {
+                comptime assertIsPageArg(Struct, named_function, 3);
+                @field(args, "3") = context.page;
+            }
+        },
+        else => @compileError(named_function.full_name ++ " has too many parmaters"),
+    }
+
+    const res = @call(.auto, func, args);
+    if (has_value == false) {
+        return v8.Intercepted.No;
+    }
+    info.getReturnValue().set(try context.zigValueToJs(res));
+    return v8.Intercepted.Yes;
+}
+
+pub fn getNamedIndex(self: *Caller, comptime Struct: type, comptime named_function: NamedFunction, name: v8.Name, info: v8.PropertyCallbackInfo) !u8 {
+    const context = self.context;
+    const func = @field(Struct, named_function.name);
+    comptime assertSelfReceiver(Struct, named_function);
+
+    var has_value = true;
+    var args = try self.getArgs(Struct, named_function, 3, info);
+    const zig_instance = try context.typeTaggedAnyOpaque(named_function, *types.Receiver(Struct), info.getThis());
+    @field(args, "0") = zig_instance;
+    @field(args, "1") = try self.nameToString(name);
+    @field(args, "2") = &has_value;
+
+    const res = @call(.auto, func, args);
+    if (has_value == false) {
+        return v8.Intercepted.No;
+    }
+    info.getReturnValue().set(try self.context.zigValueToJs(res));
+    return v8.Intercepted.Yes;
+}
+
+pub fn setNamedIndex(self: *Caller, comptime Struct: type, comptime named_function: NamedFunction, name: v8.Name, js_value: v8.Value, info: v8.PropertyCallbackInfo) !u8 {
+    const context = self.context;
+    const func = @field(Struct, named_function.name);
+    comptime assertSelfReceiver(Struct, named_function);
+
+    var has_value = true;
+    var args = try self.getArgs(Struct, named_function, 4, info);
+    const zig_instance = try context.typeTaggedAnyOpaque(named_function, *types.Receiver(Struct), info.getThis());
+    @field(args, "0") = zig_instance;
+    @field(args, "1") = try self.nameToString(name);
+    @field(args, "2") = try context.jsValueToZig(named_function, @TypeOf(@field(args, "2")), js_value);
+    @field(args, "3") = &has_value;
+
+    const res = @call(.auto, func, args);
+    return namedSetOrDeleteCall(res, has_value);
+}
+
+pub fn deleteNamedIndex(self: *Caller, comptime Struct: type, comptime named_function: NamedFunction, name: v8.Name, info: v8.PropertyCallbackInfo) !u8 {
+    const context = self.context;
+    const func = @field(Struct, named_function.name);
+    comptime assertSelfReceiver(Struct, named_function);
+
+    var has_value = true;
+    var args = try self.getArgs(Struct, named_function, 3, info);
+    const zig_instance = try context.typeTaggedAnyOpaque(named_function, *types.Receiver(Struct), info.getThis());
+    @field(args, "0") = zig_instance;
+    @field(args, "1") = try self.nameToString(name);
+    @field(args, "2") = &has_value;
+
+    const res = @call(.auto, func, args);
+    return namedSetOrDeleteCall(res, has_value);
+}
+
+fn namedSetOrDeleteCall(res: anytype, has_value: bool) !u8 {
+    if (@typeInfo(@TypeOf(res)) == .error_union) {
+        _ = try res;
+    }
+    if (has_value == false) {
+        return v8.Intercepted.No;
+    }
+    return v8.Intercepted.Yes;
+}
+
+fn nameToString(self: *Caller, name: v8.Name) ![]const u8 {
+    return self.context.valueToString(.{ .handle = name.handle }, .{});
+}
+
+fn isSelfReceiver(comptime Struct: type, comptime named_function: NamedFunction) bool {
+    return checkSelfReceiver(Struct, named_function, false);
+}
+fn assertSelfReceiver(comptime Struct: type, comptime named_function: NamedFunction) void {
+    _ = checkSelfReceiver(Struct, named_function, true);
+}
+fn checkSelfReceiver(comptime Struct: type, comptime named_function: NamedFunction, comptime fail: bool) bool {
+    const func = @field(Struct, named_function.name);
+    const params = @typeInfo(@TypeOf(func)).@"fn".params;
+    if (params.len == 0) {
+        if (fail) {
+            @compileError(named_function.full_name ++ " must have a self parameter");
+        }
+        return false;
+    }
+
+    const R = types.Receiver(Struct);
+    const first_param = params[0].type.?;
+    if (first_param != *R and first_param != *const R) {
+        if (fail) {
+            @compileError(std.fmt.comptimePrint("The first parameter to {s} must be a *{s} or *const {s}. Got: {s}", .{
+                named_function.full_name,
+                @typeName(R),
+                @typeName(R),
+                @typeName(first_param),
+            }));
+        }
+        return false;
+    }
+    return true;
+}
+
+fn assertIsPageArg(comptime Struct: type, comptime named_function: NamedFunction, index: comptime_int) void {
+    const F = @TypeOf(@field(Struct, named_function.name));
+    const param = @typeInfo(F).@"fn".params[index].type.?;
+    if (isPage(param)) {
+        return;
+    }
+    @compileError(std.fmt.comptimePrint("The {d} parameter to {s} must be a *Page or *const Page. Got: {s}", .{ index, named_function.full_name, @typeName(param) }));
+}
+
+pub fn handleError(self: *Caller, comptime Struct: type, comptime named_function: NamedFunction, err: anyerror, info: anytype) void {
+    const isolate = self.isolate;
+
+    if (comptime @import("builtin").mode == .Debug and @hasDecl(@TypeOf(info), "length")) {
+        if (log.enabled(.js, .warn)) {
+            self.logFunctionCallError(err, named_function.full_name, info);
+        }
+    }
+
+    var js_err: ?v8.Value = switch (err) {
+        error.InvalidArgument => createTypeException(isolate, "invalid argument"),
+        error.OutOfMemory => js._createException(isolate, "out of memory"),
+        error.IllegalConstructor => js._createException(isolate, "Illegal Contructor"),
+        else => blk: {
+            const func = @field(Struct, named_function.name);
+            const return_type = @typeInfo(@TypeOf(func)).@"fn".return_type orelse {
+                // void return type;
+                break :blk null;
+            };
+
+            if (@typeInfo(return_type) != .error_union) {
+                // type defines a custom exception, but this function should
+                // not fail. We failed somewhere inside of js.zig and
+                // should return the error as-is, since it isn't related
+                // to our Struct
+                break :blk null;
+            }
+
+            const function_error_set = @typeInfo(return_type).error_union.error_set;
+
+            const E = comptime getCustomException(Struct) orelse break :blk null;
+            if (function_error_set == E or isErrorSetException(E, err)) {
+                const custom_exception = E.init(self.call_arena, err, named_function.js_name) catch |init_err| {
+                    switch (init_err) {
+                        // if a custom exceptions' init wants to return a
+                        // different error, we need to think about how to
+                        // handle that failure.
+                        error.OutOfMemory => break :blk js._createException(isolate, "out of memory"),
+                    }
+                };
+                // ughh..how to handle an error here?
+                break :blk self.context.zigValueToJs(custom_exception) catch js._createException(isolate, "internal error");
+            }
+            // this error isn't part of a custom exception
+            break :blk null;
+        },
+    };
+
+    if (js_err == null) {
+        js_err = js._createException(isolate, @errorName(err));
+    }
+    const js_exception = isolate.throwException(js_err.?);
+    info.getReturnValue().setValueHandle(js_exception.handle);
+}
+
+// walk the prototype chain to see if a type declares a custom Exception
+fn getCustomException(comptime Struct: type) ?type {
+    var S = Struct;
+    while (true) {
+        if (@hasDecl(S, "Exception")) {
+            return S.Exception;
+        }
+        if (@hasDecl(S, "prototype") == false) {
+            return null;
+        }
+        // long ago, we validated that every prototype declaration
+        // is a pointer.
+        S = @typeInfo(S.prototype).pointer.child;
+    }
+}
+
+// Does the error we want to return belong to the custom exeception's ErrorSet
+fn isErrorSetException(comptime E: type, err: anytype) bool {
+    const Entry = std.meta.Tuple(&.{ []const u8, void });
+
+    const error_set = @typeInfo(E.ErrorSet).error_set.?;
+    const entries = comptime blk: {
+        var kv: [error_set.len]Entry = undefined;
+        for (error_set, 0..) |e, i| {
+            kv[i] = .{ e.name, {} };
+        }
+        break :blk kv;
+    };
+    const lookup = std.StaticStringMap(void).initComptime(entries);
+    return lookup.has(@errorName(err));
+}
+
+// If we call a method in javascript: cat.lives('nine');
+//
+// Then we'd expect a Zig function with 2 parameters: a self and the string.
+// In this case, offset == 1. Offset is always 1 for setters or methods.
+//
+// Offset is always 0 for constructors.
+//
+// For constructors, setters and methods, we can further increase offset + 1
+// if the first parameter is an instance of Page.
+//
+// Finally, if the JS function is called with _more_ parameters and
+// the last parameter in Zig is an array, we'll try to slurp the additional
+// parameters into the array.
+fn getArgs(self: *const Caller, comptime Struct: type, comptime named_function: NamedFunction, comptime offset: usize, info: anytype) !ParamterTypes(@TypeOf(@field(Struct, named_function.name))) {
+    const context = self.context;
+    const F = @TypeOf(@field(Struct, named_function.name));
+    var args: ParamterTypes(F) = undefined;
+
+    const params = @typeInfo(F).@"fn".params[offset..];
+    // Except for the constructor, the first parameter is always `self`
+    // This isn't something we'll bind from JS, so skip it.
+    const params_to_map = blk: {
+        if (params.len == 0) {
+            return args;
+        }
+
+        // If the last parameter is the Page, set it, and exclude it
+        // from our params slice, because we don't want to bind it to
+        // a JS argument
+        if (comptime isPage(params[params.len - 1].type.?)) {
+            @field(args, tupleFieldName(params.len - 1 + offset)) = self.context.page;
+            break :blk params[0 .. params.len - 1];
+        }
+
+        // If the last parameter is a special JsThis, set it, and exclude it
+        // from our params slice, because we don't want to bind it to
+        // a JS argument
+        if (comptime params[params.len - 1].type.? == js.This) {
+            @field(args, tupleFieldName(params.len - 1 + offset)) = .{ .obj = .{
+                .context = context,
+                .js_obj = info.getThis(),
+            } };
+
+            // AND the 2nd last parameter is state
+            if (params.len > 1 and comptime isPage(params[params.len - 2].type.?)) {
+                @field(args, tupleFieldName(params.len - 2 + offset)) = self.context.page;
+                break :blk params[0 .. params.len - 2];
+            }
+
+            break :blk params[0 .. params.len - 1];
+        }
+
+        // we have neither a Page nor a JsObject. All params must be
+        // bound to a JavaScript value.
+        break :blk params;
+    };
+
+    if (params_to_map.len == 0) {
+        return args;
+    }
+
+    const js_parameter_count = info.length();
+    const last_js_parameter = params_to_map.len - 1;
+    var is_variadic = false;
+
+    {
+        // This is going to get complicated. If the last Zig parameter
+        // is a slice AND the corresponding javascript parameter is
+        // NOT an an array, then we'll treat it as a variadic.
+
+        const last_parameter_type = params_to_map[params_to_map.len - 1].type.?;
+        const last_parameter_type_info = @typeInfo(last_parameter_type);
+        if (last_parameter_type_info == .pointer and last_parameter_type_info.pointer.size == .slice) {
+            const slice_type = last_parameter_type_info.pointer.child;
+            const corresponding_js_value = info.getArg(@as(u32, @intCast(last_js_parameter)));
+            if (corresponding_js_value.isArray() == false and corresponding_js_value.isTypedArray() == false and slice_type != u8) {
+                is_variadic = true;
+                if (js_parameter_count == 0) {
+                    @field(args, tupleFieldName(params_to_map.len + offset - 1)) = &.{};
+                } else if (js_parameter_count >= params_to_map.len) {
+                    const arr = try self.call_arena.alloc(last_parameter_type_info.pointer.child, js_parameter_count - params_to_map.len + 1);
+                    for (arr, last_js_parameter..) |*a, i| {
+                        const js_value = info.getArg(@as(u32, @intCast(i)));
+                        a.* = try context.jsValueToZig(named_function, slice_type, js_value);
+                    }
+                    @field(args, tupleFieldName(params_to_map.len + offset - 1)) = arr;
+                } else {
+                    @field(args, tupleFieldName(params_to_map.len + offset - 1)) = &.{};
+                }
+            }
+        }
+    }
+
+    inline for (params_to_map, 0..) |param, i| {
+        const field_index = comptime i + offset;
+        if (comptime i == params_to_map.len - 1) {
+            if (is_variadic) {
+                break;
+            }
+        }
+
+        if (comptime isPage(param.type.?)) {
+            @compileError("Page must be the last parameter (or 2nd last if there's a JsThis): " ++ named_function.full_name);
+        } else if (comptime param.type.? == js.This) {
+            @compileError("JsThis must be the last parameter: " ++ named_function.full_name);
+        } else if (i >= js_parameter_count) {
+            if (@typeInfo(param.type.?) != .optional) {
+                return error.InvalidArgument;
+            }
+            @field(args, tupleFieldName(field_index)) = null;
+        } else {
+            const js_value = info.getArg(@as(u32, @intCast(i)));
+            @field(args, tupleFieldName(field_index)) = context.jsValueToZig(named_function, param.type.?, js_value) catch {
+                return error.InvalidArgument;
+            };
+        }
+    }
+
+    return args;
+}
+
+// This is extracted to speed up compilation. When left inlined in handleError,
+// this can add as much as 10 seconds of compilation time.
+fn logFunctionCallError(self: *Caller, err: anyerror, function_name: []const u8, info: v8.FunctionCallbackInfo) void {
+    const args_dump = self.serializeFunctionArgs(info) catch "failed to serialize args";
+    log.info(.js, "function call error", .{
+        .name = function_name,
+        .err = err,
+        .args = args_dump,
+        .stack = self.context.stackTrace() catch |err1| @errorName(err1),
+    });
+}
+
+fn serializeFunctionArgs(self: *Caller, info: v8.FunctionCallbackInfo) ![]const u8 {
+    const separator = log.separator();
+    const js_parameter_count = info.length();
+
+    const context = self.context;
+    var arr: std.ArrayListUnmanaged(u8) = .{};
+    for (0..js_parameter_count) |i| {
+        const js_value = info.getArg(@intCast(i));
+        const value_string = try context.valueToDetailString(js_value);
+        const value_type = try context.jsStringToZig(try js_value.typeOf(self.isolate), .{});
+        try std.fmt.format(arr.writer(context.call_arena), "{s}{d}: {s} ({s})", .{
+            separator,
+            i + 1,
+            value_string,
+            value_type,
+        });
+    }
+    return arr.items;
+}
+
+// We want the function name, or more precisely, the "Struct.function" for
+// displaying helpful @compileError.
+// However, there's no way to get the name from a std.Builtin.Fn, so we create
+// a NamedFunction as part of our binding, and pass it around incase we need
+// to display an error
+pub const NamedFunction = struct {
+    name: []const u8,
+    js_name: []const u8,
+    full_name: []const u8,
+
+    pub fn init(comptime Struct: type, comptime name: []const u8) NamedFunction {
+        return .{
+            .name = name,
+            .js_name = if (name[0] == '_') name[1..] else name,
+            .full_name = @typeName(Struct) ++ "." ++ name,
+        };
+    }
+};
+
+// Takes a function, and returns a tuple for its argument. Used when we
+// @call a function
+fn ParamterTypes(comptime F: type) type {
+    const params = @typeInfo(F).@"fn".params;
+    var fields: [params.len]std.builtin.Type.StructField = undefined;
+
+    inline for (params, 0..) |param, i| {
+        fields[i] = .{
+            .name = tupleFieldName(i),
+            .type = param.type.?,
+            .default_value_ptr = null,
+            .is_comptime = false,
+            .alignment = @alignOf(param.type.?),
+        };
+    }
+
+    return @Type(.{ .@"struct" = .{
+        .layout = .auto,
+        .decls = &.{},
+        .fields = &fields,
+        .is_tuple = true,
+    } });
+}
+
+fn tupleFieldName(comptime i: usize) [:0]const u8 {
+    return switch (i) {
+        0 => "0",
+        1 => "1",
+        2 => "2",
+        3 => "3",
+        4 => "4",
+        5 => "5",
+        6 => "6",
+        7 => "7",
+        8 => "8",
+        9 => "9",
+        else => std.fmt.comptimePrint("{d}", .{i}),
+    };
+}
+
+fn isPage(comptime T: type) bool {
+    return T == *Page or T == *const Page;
+}
+
+fn createTypeException(isolate: v8.Isolate, msg: []const u8) v8.Value {
+    return v8.Exception.initTypeError(v8.String.initUtf8(isolate, msg));
+}

src/browser/js/Env.zig

@@ -0,0 +1,539 @@
+const std = @import("std");
+const js = @import("js.zig");
+const v8 = js.v8;
+
+const log = @import("../../log.zig");
+
+const types = @import("types.zig");
+const Types = types.Types;
+const Caller = @import("Caller.zig");
+const Context = @import("Context.zig");
+const Platform = @import("Platform.zig");
+const Inspector = @import("Inspector.zig");
+const ExecutionWorld = @import("ExecutionWorld.zig");
+const NamedFunction = Caller.NamedFunction;
+
+const Allocator = std.mem.Allocator;
+const ArenaAllocator = std.heap.ArenaAllocator;
+
+// The Env maps to a V8 isolate, which represents a isolated sandbox for
+// executing JavaScript. The Env is where we'll define our V8 <-> Zig bindings,
+// and it's where we'll start ExecutionWorlds, which actually execute JavaScript.
+// The `S` parameter is arbitrary state. When we start an ExecutionWorld, an instance
+// of S must be given. This instance is available to any Zig binding.
+// The `types` parameter is a tuple of Zig structures we want to bind to V8.
+const Env = @This();
+
+allocator: Allocator,
+
+platform: *const Platform,
+
+// the global isolate
+isolate: v8.Isolate,
+
+// just kept around because we need to free it on deinit
+isolate_params: *v8.CreateParams,
+
+// Given a type, we can lookup its index in TYPE_LOOKUP and then have
+// access to its TunctionTemplate (the thing we need to create an instance
+// of it)
+// I.e.:
+// const index = @field(TYPE_LOOKUP, @typeName(type_name))
+// const template = templates[index];
+templates: [Types.len]v8.FunctionTemplate,
+
+// Given a type index (retrieved via the TYPE_LOOKUP), we can retrieve
+// the index of its prototype. Types without a prototype have their own
+// index.
+prototype_lookup: [Types.len]u16,
+
+meta_lookup: [Types.len]types.Meta,
+
+context_id: usize,
+
+const Opts = struct {};
+
+pub fn init(allocator: Allocator, platform: *const Platform, _: Opts) !*Env {
+    // var params = v8.initCreateParams();
+    var params = try allocator.create(v8.CreateParams);
+    errdefer allocator.destroy(params);
+
+    v8.c.v8__Isolate__CreateParams__CONSTRUCT(params);
+
+    params.array_buffer_allocator = v8.createDefaultArrayBufferAllocator();
+    errdefer v8.destroyArrayBufferAllocator(params.array_buffer_allocator.?);
+
+    var isolate = v8.Isolate.init(params);
+    errdefer isolate.deinit();
+
+    // This is the callback that runs whenever a module is dynamically imported.
+    isolate.setHostImportModuleDynamicallyCallback(Context.dynamicModuleCallback);
+    isolate.setPromiseRejectCallback(promiseRejectCallback);
+    isolate.setMicrotasksPolicy(v8.c.kExplicit);
+
+    isolate.enter();
+    errdefer isolate.exit();
+
+    isolate.setHostInitializeImportMetaObjectCallback(Context.metaObjectCallback);
+
+    var temp_scope: v8.HandleScope = undefined;
+    v8.HandleScope.init(&temp_scope, isolate);
+    defer temp_scope.deinit();
+
+    const env = try allocator.create(Env);
+    errdefer allocator.destroy(env);
+
+    env.* = .{
+        .context_id = 0,
+        .platform = platform,
+        .isolate = isolate,
+        .templates = undefined,
+        .allocator = allocator,
+        .isolate_params = params,
+        .meta_lookup = undefined,
+        .prototype_lookup = undefined,
+    };
+
+    // Populate our templates lookup. generateClass creates the
+    // v8.FunctionTemplate, which we store in our env.templates.
+    // The ordering doesn't matter. What matters is that, given a type
+    // we can get its index via: @field(types.LOOKUP, type_name)
+    const templates = &env.templates;
+    inline for (Types, 0..) |s, i| {
+        @setEvalBranchQuota(10_000);
+        templates[i] = v8.Persistent(v8.FunctionTemplate).init(isolate, generateClass(s.defaultValue().?, isolate)).castToFunctionTemplate();
+    }
+
+    // Above, we've created all our our FunctionTemplates. Now that we
+    // have them all, we can hook up the prototypes.
+    const meta_lookup = &env.meta_lookup;
+    inline for (Types, 0..) |s, i| {
+        const Struct = s.defaultValue().?;
+        if (@hasDecl(Struct, "prototype")) {
+            const TI = @typeInfo(Struct.prototype);
+            const proto_name = @typeName(types.Receiver(TI.pointer.child));
+            if (@hasField(types.Lookup, proto_name) == false) {
+                @compileError(std.fmt.comptimePrint("Prototype '{s}' for '{s}' is undefined", .{ proto_name, @typeName(Struct) }));
+            }
+            // Hey, look! This is our first real usage of the types.LOOKUP.
+            // Just like we said above, given a type, we can get its
+            // template index.
+
+            const proto_index = @field(types.LOOKUP, proto_name);
+            templates[i].inherit(templates[proto_index]);
+        }
+
+        // while we're here, let's populate our meta lookup
+        const subtype: ?types.Sub = if (@hasDecl(Struct, "subtype")) Struct.subtype else null;
+
+        const proto_offset = comptime blk: {
+            if (!@hasField(Struct, "proto")) {
+                break :blk 0;
+            }
+            const proto_info = std.meta.fieldInfo(Struct, .proto);
+            if (@typeInfo(proto_info.type) == .pointer) {
+                // we store the offset as a negative, to so that,
+                // when we reverse this, we know that it's
+                // behind a pointer that we need to resolve.
+                break :blk -@offsetOf(Struct, "proto");
+            }
+            break :blk @offsetOf(Struct, "proto");
+        };
+
+        meta_lookup[i] = .{
+            .index = i,
+            .subtype = subtype,
+            .proto_offset = proto_offset,
+        };
+    }
+
+    return env;
+}
+
+pub fn deinit(self: *Env) void {
+    self.isolate.exit();
+    self.isolate.deinit();
+    v8.destroyArrayBufferAllocator(self.isolate_params.array_buffer_allocator.?);
+    self.allocator.destroy(self.isolate_params);
+    self.allocator.destroy(self);
+}
+
+pub fn newInspector(self: *Env, arena: Allocator, ctx: anytype) !Inspector {
+    return Inspector.init(arena, self.isolate, ctx);
+}
+
+pub fn runMicrotasks(self: *const Env) void {
+    self.isolate.performMicrotasksCheckpoint();
+}
+
+pub fn pumpMessageLoop(self: *const Env) bool {
+    return self.platform.inner.pumpMessageLoop(self.isolate, false);
+}
+
+pub fn runIdleTasks(self: *const Env) void {
+    return self.platform.inner.runIdleTasks(self.isolate, 1);
+}
+
+pub fn newExecutionWorld(self: *Env) !ExecutionWorld {
+    return .{
+        .env = self,
+        .context = null,
+        .context_arena = ArenaAllocator.init(self.allocator),
+    };
+}
+
+// V8 doesn't immediately free memory associated with
+// a Context, it's managed by the garbage collector. We use the
+// `lowMemoryNotification` call on the isolate to encourage v8 to free
+// any contexts which have been freed.
+pub fn lowMemoryNotification(self: *Env) void {
+    var handle_scope: v8.HandleScope = undefined;
+    v8.HandleScope.init(&handle_scope, self.isolate);
+    defer handle_scope.deinit();
+    self.isolate.lowMemoryNotification();
+}
+
+pub fn dumpMemoryStats(self: *Env) void {
+    const stats = self.isolate.getHeapStatistics();
+    std.debug.print(
+        \\ Total Heap Size: {d}
+        \\ Total Heap Size Executable: {d}
+        \\ Total Physical Size: {d}
+        \\ Total Available Size: {d}
+        \\ Used Heap Size: {d}
+        \\ Heap Size Limit: {d}
+        \\ Malloced Memory: {d}
+        \\ External Memory: {d}
+        \\ Peak Malloced Memory: {d}
+        \\ Number Of Native Contexts: {d}
+        \\ Number Of Detached Contexts: {d}
+        \\ Total Global Handles Size: {d}
+        \\ Used Global Handles Size: {d}
+        \\ Zap Garbage: {any}
+        \\
+    , .{ stats.total_heap_size, stats.total_heap_size_executable, stats.total_physical_size, stats.total_available_size, stats.used_heap_size, stats.heap_size_limit, stats.malloced_memory, stats.external_memory, stats.peak_malloced_memory, stats.number_of_native_contexts, stats.number_of_detached_contexts, stats.total_global_handles_size, stats.used_global_handles_size, stats.does_zap_garbage });
+}
+
+fn promiseRejectCallback(v8_msg: v8.C_PromiseRejectMessage) callconv(.c) void {
+    const msg = v8.PromiseRejectMessage.initFromC(v8_msg);
+    const isolate = msg.getPromise().toObject().getIsolate();
+    const context = Context.fromIsolate(isolate);
+
+    const value =
+        if (msg.getValue()) |v8_value| context.valueToString(v8_value, .{}) catch |err| @errorName(err) else "no value";
+
+    log.debug(.js, "unhandled rejection", .{ .value = value });
+}
+
+// Give it a Zig struct, get back a v8.FunctionTemplate.
+// The FunctionTemplate is a bit like a struct container - it's where
+// we'll attach functions/getters/setters and where we'll "inherit" a
+// prototype type (if there is any)
+fn generateClass(comptime Struct: type, isolate: v8.Isolate) v8.FunctionTemplate {
+    const template = generateConstructor(Struct, isolate);
+    attachClass(Struct, isolate, template);
+    return template;
+}
+
+// Normally this is called from generateClass. Where generateClass creates
+// the constructor (hence, the FunctionTemplate), attachClass adds all
+// of its functions, getters, setters, ...
+// But it's extracted from generateClass because we also have 1 global
+// object (i.e. the Window), which gets attached not only to the Window
+// constructor/FunctionTemplate as normal, but also through the default
+// FunctionTemplate of the isolate (in createContext)
+pub fn attachClass(comptime Struct: type, isolate: v8.Isolate, template: v8.FunctionTemplate) void {
+    const template_proto = template.getPrototypeTemplate();
+    inline for (@typeInfo(Struct).@"struct".decls) |declaration| {
+        const name = declaration.name;
+        if (comptime name[0] == '_') {
+            switch (@typeInfo(@TypeOf(@field(Struct, name)))) {
+                .@"fn" => generateMethod(Struct, name, isolate, template_proto),
+                else => |ti| if (!comptime js.isComplexAttributeType(ti)) {
+                    generateAttribute(Struct, name, isolate, template, template_proto);
+                },
+            }
+        } else if (comptime std.mem.startsWith(u8, name, "get_")) {
+            generateProperty(Struct, name[4..], isolate, template_proto);
+        } else if (comptime std.mem.startsWith(u8, name, "static_")) {
+            generateFunction(Struct, name[7..], isolate, template);
+        }
+    }
+
+    if (@hasDecl(Struct, "get_symbol_toStringTag") == false) {
+        // If this WAS defined, then we would have created it in generateProperty.
+        // But if it isn't, we create a default one
+        const string_tag_callback = v8.FunctionTemplate.initCallback(isolate, struct {
+            fn stringTag(raw_info: ?*const v8.C_FunctionCallbackInfo) callconv(.c) void {
+                const info = v8.FunctionCallbackInfo.initFromV8(raw_info);
+                const class_name = v8.String.initUtf8(info.getIsolate(), comptime js.classNameForStruct(Struct));
+                info.getReturnValue().set(class_name);
+            }
+        }.stringTag);
+        const key = v8.Symbol.getToStringTag(isolate).toName();
+        template_proto.setAccessorGetter(key, string_tag_callback);
+    }
+
+    generateIndexer(Struct, template_proto);
+    generateNamedIndexer(Struct, template.getInstanceTemplate());
+    generateUndetectable(Struct, template.getInstanceTemplate());
+}
+
+// Even if a struct doesn't have a `constructor` function, we still
+// `generateConstructor`, because this is how we create our
+// FunctionTemplate. Such classes exist, but they can't be instantiated
+// via `new ClassName()` - but they could, for example, be created in
+// Zig and returned from a function call, which is why we need the
+// FunctionTemplate.
+fn generateConstructor(comptime Struct: type, isolate: v8.Isolate) v8.FunctionTemplate {
+    const template = v8.FunctionTemplate.initCallback(isolate, struct {
+        fn callback(raw_info: ?*const v8.C_FunctionCallbackInfo) callconv(.c) void {
+            const info = v8.FunctionCallbackInfo.initFromV8(raw_info);
+            var caller = Caller.init(info);
+            defer caller.deinit();
+            // See comment above. We generateConstructor on all types
+            // in order to create the FunctionTemplate, but there might
+            // not be an actual "constructor" function. So if someone
+            // does `new ClassName()` where ClassName doesn't have
+            // a constructor function, we'll return an error.
+            if (@hasDecl(Struct, "constructor") == false) {
+                const iso = caller.isolate;
+                log.warn(.js, "Illegal constructor call", .{ .name = @typeName(Struct) });
+                const js_exception = iso.throwException(js._createException(iso, "Illegal Constructor"));
+                info.getReturnValue().set(js_exception);
+                return;
+            }
+
+            // Safe to call now, because if Struct.constructor didn't
+            // exist, the above if block would have returned.
+            const named_function = comptime NamedFunction.init(Struct, "constructor");
+            caller.constructor(Struct, named_function, info) catch |err| {
+                caller.handleError(Struct, named_function, err, info);
+            };
+        }
+    }.callback);
+
+    if (comptime types.isEmpty(types.Receiver(Struct)) == false) {
+        // If the struct is empty, we won't store a Zig reference inside
+        // the JS object, so we don't need to set the internal field count
+        template.getInstanceTemplate().setInternalFieldCount(1);
+    }
+
+    const class_name = v8.String.initUtf8(isolate, comptime js.classNameForStruct(Struct));
+    template.setClassName(class_name);
+    return template;
+}
+
+fn generateMethod(comptime Struct: type, comptime name: []const u8, isolate: v8.Isolate, template_proto: v8.ObjectTemplate) void {
+    var js_name: v8.Name = undefined;
+    if (comptime std.mem.eql(u8, name, "_symbol_iterator")) {
+        js_name = v8.Symbol.getIterator(isolate).toName();
+    } else {
+        js_name = v8.String.initUtf8(isolate, name[1..]).toName();
+    }
+    const function_template = v8.FunctionTemplate.initCallback(isolate, struct {
+        fn callback(raw_info: ?*const v8.C_FunctionCallbackInfo) callconv(.c) void {
+            const info = v8.FunctionCallbackInfo.initFromV8(raw_info);
+            var caller = Caller.init(info);
+            defer caller.deinit();
+
+            const named_function = comptime NamedFunction.init(Struct, name);
+            caller.method(Struct, named_function, info) catch |err| {
+                caller.handleError(Struct, named_function, err, info);
+            };
+        }
+    }.callback);
+    template_proto.set(js_name, function_template, v8.PropertyAttribute.None);
+}
+
+fn generateFunction(comptime Struct: type, comptime name: []const u8, isolate: v8.Isolate, template: v8.FunctionTemplate) void {
+    const js_name = v8.String.initUtf8(isolate, name).toName();
+    const function_template = v8.FunctionTemplate.initCallback(isolate, struct {
+        fn callback(raw_info: ?*const v8.C_FunctionCallbackInfo) callconv(.c) void {
+            const info = v8.FunctionCallbackInfo.initFromV8(raw_info);
+            var caller = Caller.init(info);
+            defer caller.deinit();
+
+            const named_function = comptime NamedFunction.init(Struct, "static_" ++ name);
+            caller.function(Struct, named_function, info) catch |err| {
+                caller.handleError(Struct, named_function, err, info);
+            };
+        }
+    }.callback);
+    template.set(js_name, function_template, v8.PropertyAttribute.None);
+}
+
+fn generateAttribute(comptime Struct: type, comptime name: []const u8, isolate: v8.Isolate, template: v8.FunctionTemplate, template_proto: v8.ObjectTemplate) void {
+    const zig_value = @field(Struct, name);
+    const js_value = js.simpleZigValueToJs(isolate, zig_value, true);
+
+    const js_name = v8.String.initUtf8(isolate, name[1..]).toName();
+
+    // apply it both to the type itself
+    template.set(js_name, js_value, v8.PropertyAttribute.ReadOnly + v8.PropertyAttribute.DontDelete);
+
+    // and to instances of the type
+    template_proto.set(js_name, js_value, v8.PropertyAttribute.ReadOnly + v8.PropertyAttribute.DontDelete);
+}
+
+fn generateProperty(comptime Struct: type, comptime name: []const u8, isolate: v8.Isolate, template_proto: v8.ObjectTemplate) void {
+    var js_name: v8.Name = undefined;
+    if (comptime std.mem.eql(u8, name, "symbol_toStringTag")) {
+        js_name = v8.Symbol.getToStringTag(isolate).toName();
+    } else {
+        js_name = v8.String.initUtf8(isolate, name).toName();
+    }
+
+    const getter_callback = v8.FunctionTemplate.initCallback(isolate, struct {
+        fn callback(raw_info: ?*const v8.C_FunctionCallbackInfo) callconv(.c) void {
+            const info = v8.FunctionCallbackInfo.initFromV8(raw_info);
+            var caller = Caller.init(info);
+            defer caller.deinit();
+
+            const named_function = comptime NamedFunction.init(Struct, "get_" ++ name);
+            caller.method(Struct, named_function, info) catch |err| {
+                caller.handleError(Struct, named_function, err, info);
+            };
+        }
+    }.callback);
+
+    const setter_name = "set_" ++ name;
+    if (@hasDecl(Struct, setter_name) == false) {
+        template_proto.setAccessorGetter(js_name, getter_callback);
+        return;
+    }
+
+    const setter_callback = v8.FunctionTemplate.initCallback(isolate, struct {
+        fn callback(raw_info: ?*const v8.C_FunctionCallbackInfo) callconv(.c) void {
+            const info = v8.FunctionCallbackInfo.initFromV8(raw_info);
+            std.debug.assert(info.length() == 1);
+
+            var caller = Caller.init(info);
+            defer caller.deinit();
+
+            const named_function = comptime NamedFunction.init(Struct, "set_" ++ name);
+            caller.method(Struct, named_function, info) catch |err| {
+                caller.handleError(Struct, named_function, err, info);
+            };
+        }
+    }.callback);
+
+    template_proto.setAccessorGetterAndSetter(js_name, getter_callback, setter_callback);
+}
+
+fn generateIndexer(comptime Struct: type, template_proto: v8.ObjectTemplate) void {
+    if (@hasDecl(Struct, "indexed_get") == false) {
+        return;
+    }
+    const configuration = v8.IndexedPropertyHandlerConfiguration{
+        .getter = struct {
+            fn callback(idx: u32, raw_info: ?*const v8.C_PropertyCallbackInfo) callconv(.c) u8 {
+                const info = v8.PropertyCallbackInfo.initFromV8(raw_info);
+                var caller = Caller.init(info);
+                defer caller.deinit();
+
+                const named_function = comptime NamedFunction.init(Struct, "indexed_get");
+                return caller.getIndex(Struct, named_function, idx, info) catch |err| blk: {
+                    caller.handleError(Struct, named_function, err, info);
+                    break :blk v8.Intercepted.No;
+                };
+            }
+        }.callback,
+    };
+
+    // If you're trying to implement setter, read:
+    // https://groups.google.com/g/v8-users/c/8tahYBsHpgY/m/IteS7Wn2AAAJ
+    // The issue I had was
+    // (a) where to attache it: does it go on the instance_template
+    //     instead of the prototype?
+    // (b) defining the getter or query to respond with the
+    //     PropertyAttribute to indicate if the property can be set
+    template_proto.setIndexedProperty(configuration, null);
+}
+
+fn generateNamedIndexer(comptime Struct: type, template_proto: v8.ObjectTemplate) void {
+    if (@hasDecl(Struct, "named_get") == false) {
+        return;
+    }
+
+    var configuration = v8.NamedPropertyHandlerConfiguration{
+        .getter = struct {
+            fn callback(c_name: ?*const v8.C_Name, raw_info: ?*const v8.C_PropertyCallbackInfo) callconv(.c) u8 {
+                const info = v8.PropertyCallbackInfo.initFromV8(raw_info);
+                var caller = Caller.init(info);
+                defer caller.deinit();
+
+                const named_function = comptime NamedFunction.init(Struct, "named_get");
+                return caller.getNamedIndex(Struct, named_function, .{ .handle = c_name.? }, info) catch |err| blk: {
+                    caller.handleError(Struct, named_function, err, info);
+                    break :blk v8.Intercepted.No;
+                };
+            }
+        }.callback,
+
+        // This is really cool. Without this, we'd intercept _all_ properties
+        // even those explicitly set. So, node.length for example would get routed
+        // to our `named_get`, rather than a `get_length`. This might be
+        // useful if we run into a type that we can't model properly in Zig.
+        .flags = v8.PropertyHandlerFlags.OnlyInterceptStrings | v8.PropertyHandlerFlags.NonMasking,
+    };
+
+    if (@hasDecl(Struct, "named_set")) {
+        configuration.setter = struct {
+            fn callback(c_name: ?*const v8.C_Name, c_value: ?*const v8.C_Value, raw_info: ?*const v8.C_PropertyCallbackInfo) callconv(.c) u8 {
+                const info = v8.PropertyCallbackInfo.initFromV8(raw_info);
+                var caller = Caller.init(info);
+                defer caller.deinit();
+
+                const named_function = comptime NamedFunction.init(Struct, "named_set");
+                return caller.setNamedIndex(Struct, named_function, .{ .handle = c_name.? }, .{ .handle = c_value.? }, info) catch |err| blk: {
+                    caller.handleError(Struct, named_function, err, info);
+                    break :blk v8.Intercepted.No;
+                };
+            }
+        }.callback;
+    }
+
+    if (@hasDecl(Struct, "named_delete")) {
+        configuration.deleter = struct {
+            fn callback(c_name: ?*const v8.C_Name, raw_info: ?*const v8.C_PropertyCallbackInfo) callconv(.c) u8 {
+                const info = v8.PropertyCallbackInfo.initFromV8(raw_info);
+                var caller = Caller.init(info);
+                defer caller.deinit();
+
+                const named_function = comptime NamedFunction.init(Struct, "named_delete");
+                return caller.deleteNamedIndex(Struct, named_function, .{ .handle = c_name.? }, info) catch |err| blk: {
+                    caller.handleError(Struct, named_function, err, info);
+                    break :blk v8.Intercepted.No;
+                };
+            }
+        }.callback;
+    }
+    template_proto.setNamedProperty(configuration, null);
+}
+
+fn generateUndetectable(comptime Struct: type, template: v8.ObjectTemplate) void {
+    const has_js_call_as_function = @hasDecl(Struct, "jsCallAsFunction");
+
+    if (has_js_call_as_function) {
+        template.setCallAsFunctionHandler(struct {
+            fn callback(raw_info: ?*const v8.C_FunctionCallbackInfo) callconv(.c) void {
+                const info = v8.FunctionCallbackInfo.initFromV8(raw_info);
+                var caller = Caller.init(info);
+                defer caller.deinit();
+
+                const named_function = comptime NamedFunction.init(Struct, "jsCallAsFunction");
+                caller.method(Struct, named_function, info) catch |err| {
+                    caller.handleError(Struct, named_function, err, info);
+                };
+            }
+        }.callback);
+    }
+
+    if (@hasDecl(Struct, "mark_as_undetectable") and Struct.mark_as_undetectable) {
+        if (!has_js_call_as_function) {
+            @compileError(@typeName(Struct) ++ ": mark_as_undetectable required jsCallAsFunction to be defined. This is a hard-coded requirement in V8, because mark_as_undetectable only exists for HTMLAllCollection which is also callable.");
+        }
+        template.markAsUndetectable();
+    }
+}

src/browser/js/ExecutionWorld.zig

@@ -0,0 +1,251 @@
+const std = @import("std");
+const js = @import("js.zig");
+const v8 = js.v8;
+
+const log = @import("../../log.zig");
+const Page = @import("../page.zig").Page;
+const ScriptManager = @import("../ScriptManager.zig");
+
+const types = @import("types.zig");
+const Types = types.Types;
+const Env = @import("Env.zig");
+const Context = @import("Context.zig");
+
+const ArenaAllocator = std.heap.ArenaAllocator;
+
+const CONTEXT_ARENA_RETAIN = 1024 * 64;
+
+// ExecutionWorld closely models a JS World.
+// https://chromium.googlesource.com/chromium/src/+/master/third_party/blink/renderer/bindings/core/v8/V8BindingDesign.md#World
+// https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/scripting/ExecutionWorld
+const ExecutionWorld = @This();
+env: *Env,
+
+// Arena whose lifetime is for a single page load. Where
+// the call_arena lives for a single function call, the context_arena
+// lives for the lifetime of the entire page. The allocator will be
+// owned by the Context, but the arena itself is owned by the ExecutionWorld
+// so that we can re-use it from context to context.
+context_arena: ArenaAllocator,
+
+// Currently a context maps to a Browser's Page. Here though, it's only a
+// mechanism to organization page-specific memory. The ExecutionWorld
+// does all the work, but having all page-specific data structures
+// grouped together helps keep things clean.
+context: ?Context = null,
+
+// no init, must be initialized via env.newExecutionWorld()
+
+pub fn deinit(self: *ExecutionWorld) void {
+    if (self.context != null) {
+        self.removeContext();
+    }
+
+    self.context_arena.deinit();
+}
+
+// Only the top Context in the Main ExecutionWorld should hold a handle_scope.
+// A v8.HandleScope is like an arena. Once created, any "Local" that
+// v8 creates will be released (or at least, releasable by the v8 GC)
+// when the handle_scope is freed.
+// We also maintain our own "context_arena" which allows us to have
+// all page related memory easily managed.
+pub fn createContext(self: *ExecutionWorld, page: *Page, enter: bool, global_callback: ?js.GlobalMissingCallback) !*Context {
+    std.debug.assert(self.context == null);
+
+    const env = self.env;
+    const isolate = env.isolate;
+    const Global = @TypeOf(page.window);
+    const templates = &self.env.templates;
+
+    var v8_context: v8.Context = blk: {
+        var temp_scope: v8.HandleScope = undefined;
+        v8.HandleScope.init(&temp_scope, isolate);
+        defer temp_scope.deinit();
+
+        const js_global = v8.FunctionTemplate.initDefault(isolate);
+        Env.attachClass(Global, isolate, js_global);
+
+        const global_template = js_global.getInstanceTemplate();
+        global_template.setInternalFieldCount(1);
+
+        // Configure the missing property callback on the global
+        // object.
+        if (global_callback != null) {
+            const configuration = v8.NamedPropertyHandlerConfiguration{
+                .getter = struct {
+                    fn callback(c_name: ?*const v8.C_Name, raw_info: ?*const v8.C_PropertyCallbackInfo) callconv(.c) u8 {
+                        const info = v8.PropertyCallbackInfo.initFromV8(raw_info);
+                        const context = Context.fromIsolate(info.getIsolate());
+
+                        const property = context.valueToString(.{ .handle = c_name.? }, .{}) catch "???";
+                        if (context.global_callback.?.missing(property, context)) {
+                            return v8.Intercepted.Yes;
+                        }
+                        return v8.Intercepted.No;
+                    }
+                }.callback,
+                .flags = v8.PropertyHandlerFlags.NonMasking | v8.PropertyHandlerFlags.OnlyInterceptStrings,
+            };
+            global_template.setNamedProperty(configuration, null);
+        }
+
+        // All the FunctionTemplates that we created and setup in Env.init
+        // are now going to get associated with our global instance.
+        inline for (Types, 0..) |s, i| {
+            const Struct = s.defaultValue().?;
+            const class_name = v8.String.initUtf8(isolate, comptime js.classNameForStruct(Struct));
+            global_template.set(class_name.toName(), templates[i], v8.PropertyAttribute.None);
+        }
+
+        // The global object (Window) has already been hooked into the v8
+        // engine when the Env was initialized - like every other type.
+        // But the V8 global is its own FunctionTemplate instance so even
+        // though it's also a Window, we need to set the prototype for this
+        // specific instance of the the Window.
+        if (@hasDecl(Global, "prototype")) {
+            const proto_type = types.Receiver(@typeInfo(Global.prototype).pointer.child);
+            const proto_name = @typeName(proto_type);
+            const proto_index = @field(types.LOOKUP, proto_name);
+            js_global.inherit(templates[proto_index]);
+        }
+
+        const context_local = v8.Context.init(isolate, global_template, null);
+        const v8_context = v8.Persistent(v8.Context).init(isolate, context_local).castToContext();
+        v8_context.enter();
+        errdefer if (enter) v8_context.exit();
+        defer if (!enter) v8_context.exit();
+
+        // This shouldn't be necessary, but it is:
+        // https://groups.google.com/g/v8-users/c/qAQQBmbi--8
+        // TODO: see if newer V8 engines have a way around this.
+        inline for (Types, 0..) |s, i| {
+            const Struct = s.defaultValue().?;
+
+            if (@hasDecl(Struct, "prototype")) {
+                const proto_type = types.Receiver(@typeInfo(Struct.prototype).pointer.child);
+                const proto_name = @typeName(proto_type);
+                if (@hasField(types.Lookup, proto_name) == false) {
+                    @compileError("Type '" ++ @typeName(Struct) ++ "' defines an unknown prototype: " ++ proto_name);
+                }
+
+                const proto_index = @field(types.LOOKUP, proto_name);
+                const proto_obj = templates[proto_index].getFunction(v8_context).toObject();
+
+                const self_obj = templates[i].getFunction(v8_context).toObject();
+                _ = self_obj.setPrototype(v8_context, proto_obj);
+            }
+        }
+        break :blk v8_context;
+    };
+
+    // For a Page we only create one HandleScope, it is stored in the main World (enter==true). A page can have multple contexts, 1 for each World.
+    // The main Context that enters and holds the HandleScope should therefore always be created first. Following other worlds for this page
+    // like isolated Worlds, will thereby place their objects on the main page's HandleScope. Note: In the furure the number of context will multiply multiple frames support
+    var handle_scope: ?v8.HandleScope = null;
+    if (enter) {
+        handle_scope = @as(v8.HandleScope, undefined);
+        v8.HandleScope.init(&handle_scope.?, isolate);
+    }
+    errdefer if (enter) handle_scope.?.deinit();
+
+    {
+        // If we want to overwrite the built-in console, we have to
+        // delete the built-in one.
+        const js_obj = v8_context.getGlobal();
+        const console_key = v8.String.initUtf8(isolate, "console");
+        if (js_obj.deleteValue(v8_context, console_key) == false) {
+            return error.ConsoleDeleteError;
+        }
+    }
+    const context_id = env.context_id;
+    env.context_id = context_id + 1;
+
+    self.context = Context{
+        .page = page,
+        .id = context_id,
+        .isolate = isolate,
+        .v8_context = v8_context,
+        .templates = &env.templates,
+        .meta_lookup = &env.meta_lookup,
+        .handle_scope = handle_scope,
+        .script_manager = &page.script_manager,
+        .call_arena = page.call_arena,
+        .arena = self.context_arena.allocator(),
+        .global_callback = global_callback,
+    };
+
+    var context = &self.context.?;
+    {
+        // Store a pointer to our context inside the v8 context so that, given
+        // a v8 context, we can get our context out
+        const data = isolate.initBigIntU64(@intCast(@intFromPtr(context)));
+        v8_context.setEmbedderData(1, data);
+    }
+
+    // Custom exception
+    // NOTE: there is no way in v8 to subclass the Error built-in type
+    // TODO: this is an horrible hack
+    inline for (Types) |s| {
+        const Struct = s.defaultValue().?;
+        if (@hasDecl(Struct, "ErrorSet")) {
+            const script = comptime js.classNameForStruct(Struct) ++ ".prototype.__proto__ = Error.prototype";
+            _ = try context.exec(script, "errorSubclass");
+        }
+    }
+
+    // Primitive attributes are set directly on the FunctionTemplate
+    // when we setup the environment. But we cannot set more complex
+    // types (v8 will crash).
+    //
+    // Plus, just to create more complex types, we always need a
+    // context, i.e. an Array has to have a Context to exist.
+    //
+    // As far as I can tell, getting the FunctionTemplate's object
+    // and setting values directly on it, for each context, is the
+    // way to do this.
+    inline for (Types, 0..) |s, i| {
+        const Struct = s.defaultValue().?;
+        inline for (@typeInfo(Struct).@"struct".decls) |declaration| {
+            const name = declaration.name;
+            if (comptime name[0] == '_') {
+                const value = @field(Struct, name);
+
+                if (comptime js.isComplexAttributeType(@typeInfo(@TypeOf(value)))) {
+                    const js_obj = templates[i].getFunction(v8_context).toObject();
+                    const js_name = v8.String.initUtf8(isolate, name[1..]).toName();
+                    const js_val = try context.zigValueToJs(value);
+                    if (!js_obj.setValue(v8_context, js_name, js_val)) {
+                        log.fatal(.app, "set class attribute", .{
+                            .@"struct" = @typeName(Struct),
+                            .name = name,
+                        });
+                    }
+                }
+            }
+        }
+    }
+
+    try context.setupGlobal();
+    return context;
+}
+
+pub fn removeContext(self: *ExecutionWorld) void {
+    // Force running the micro task to drain the queue before reseting the
+    // context arena.
+    // Tasks in the queue are relying to the arena memory could be present in
+    // the queue. Running them later could lead to invalid memory accesses.
+    self.env.runMicrotasks();
+
+    self.context.?.deinit();
+    self.context = null;
+    _ = self.context_arena.reset(.{ .retain_with_limit = CONTEXT_ARENA_RETAIN });
+}
+
+pub fn terminateExecution(self: *const ExecutionWorld) void {
+    self.env.isolate.terminateExecution();
+}
+
+pub fn resumeExecution(self: *const ExecutionWorld) void {
+    self.env.isolate.cancelTerminateExecution();
+}

src/browser/js/Function.zig

@@ -0,0 +1,144 @@
+const std = @import("std");
+const js = @import("js.zig");
+const v8 = js.v8;
+
+const Caller = @import("Caller.zig");
+const Context = @import("Context.zig");
+const PersistentFunction = v8.Persistent(v8.Function);
+
+const Allocator = std.mem.Allocator;
+
+const Function = @This();
+
+id: usize,
+context: *js.Context,
+this: ?v8.Object = null,
+func: PersistentFunction,
+
+pub const Result = struct {
+    stack: ?[]const u8,
+    exception: []const u8,
+};
+
+pub fn getName(self: *const Function, allocator: Allocator) ![]const u8 {
+    const name = self.func.castToFunction().getName();
+    return self.context.valueToString(name, .{ .allocator = allocator });
+}
+
+pub fn setName(self: *const Function, name: []const u8) void {
+    const v8_name = v8.String.initUtf8(self.context.isolate, name);
+    self.func.castToFunction().setName(v8_name);
+}
+
+pub fn withThis(self: *const Function, value: anytype) !Function {
+    const this_obj = if (@TypeOf(value) == js.Object)
+        value.js_obj
+    else
+        (try self.context.zigValueToJs(value)).castTo(v8.Object);
+
+    return .{
+        .id = self.id,
+        .this = this_obj,
+        .func = self.func,
+        .context = self.context,
+    };
+}
+
+pub fn newInstance(self: *const Function, result: *Result) !js.Object {
+    const context = self.context;
+
+    var try_catch: js.TryCatch = undefined;
+    try_catch.init(context);
+    defer try_catch.deinit();
+
+    // This creates a new instance using this Function as a constructor.
+    // This returns a generic Object
+    const js_obj = self.func.castToFunction().initInstance(context.v8_context, &.{}) orelse {
+        if (try_catch.hasCaught()) {
+            const allocator = context.call_arena;
+            result.stack = try_catch.stack(allocator) catch null;
+            result.exception = (try_catch.exception(allocator) catch "???") orelse "???";
+        } else {
+            result.stack = null;
+            result.exception = "???";
+        }
+        return error.JsConstructorFailed;
+    };
+
+    return .{
+        .context = context,
+        .js_obj = js_obj,
+    };
+}
+
+pub fn call(self: *const Function, comptime T: type, args: anytype) !T {
+    return self.callWithThis(T, self.getThis(), args);
+}
+
+pub fn tryCall(self: *const Function, comptime T: type, args: anytype, result: *Result) !T {
+    return self.tryCallWithThis(T, self.getThis(), args, result);
+}
+
+pub fn tryCallWithThis(self: *const Function, comptime T: type, this: anytype, args: anytype, result: *Result) !T {
+    var try_catch: js.TryCatch = undefined;
+    try_catch.init(self.context);
+    defer try_catch.deinit();
+
+    return self.callWithThis(T, this, args) catch |err| {
+        if (try_catch.hasCaught()) {
+            const allocator = self.context.call_arena;
+            result.stack = try_catch.stack(allocator) catch null;
+            result.exception = (try_catch.exception(allocator) catch @errorName(err)) orelse @errorName(err);
+        } else {
+            result.stack = null;
+            result.exception = @errorName(err);
+        }
+        return err;
+    };
+}
+
+pub fn callWithThis(self: *const Function, comptime T: type, this: anytype, args: anytype) !T {
+    const context = self.context;
+
+    const js_this = try context.valueToExistingObject(this);
+
+    const aargs = if (comptime @typeInfo(@TypeOf(args)) == .null) struct {}{} else args;
+
+    const js_args: []const v8.Value = switch (@typeInfo(@TypeOf(aargs))) {
+        .@"struct" => |s| blk: {
+            const fields = s.fields;
+            var js_args: [fields.len]v8.Value = undefined;
+            inline for (fields, 0..) |f, i| {
+                js_args[i] = try context.zigValueToJs(@field(aargs, f.name));
+            }
+            const cargs: [fields.len]v8.Value = js_args;
+            break :blk &cargs;
+        },
+        .pointer => blk: {
+            var values = try context.call_arena.alloc(v8.Value, args.len);
+            for (args, 0..) |a, i| {
+                values[i] = try context.zigValueToJs(a);
+            }
+            break :blk values;
+        },
+        else => @compileError("JS Function called with invalid paremter type"),
+    };
+
+    const result = self.func.castToFunction().call(context.v8_context, js_this, js_args);
+    if (result == null) {
+        return error.JSExecCallback;
+    }
+
+    if (@typeInfo(T) == .void) return {};
+    const named_function = comptime Caller.NamedFunction.init(T, "callResult");
+    return context.jsValueToZig(named_function, T, result.?);
+}
+
+fn getThis(self: *const Function) v8.Object {
+    return self.this orelse self.context.v8_context.getGlobal();
+}
+
+pub fn src(self: *const Function) ![]const u8 {
+    const value = self.func.castToFunction().toValue();
+    return self.context.valueToString(value, .{});
+}

src/browser/js/Inspector.zig

@@ -0,0 +1,125 @@
+const std = @import("std");
+const js = @import("js.zig");
+const v8 = js.v8;
+
+const Context = @import("Context.zig");
+
+const Allocator = std.mem.Allocator;
+
+const Inspector = @This();
+
+pub const RemoteObject = v8.RemoteObject;
+
+isolate: v8.Isolate,
+inner: *v8.Inspector,
+session: v8.InspectorSession,
+
+// We expect allocator to be an arena
+pub fn init(allocator: Allocator, isolate: v8.Isolate, ctx: anytype) !Inspector {
+    const ContextT = @TypeOf(ctx);
+
+    const InspectorContainer = switch (@typeInfo(ContextT)) {
+        .@"struct" => ContextT,
+        .pointer => |ptr| ptr.child,
+        .void => NoopInspector,
+        else => @compileError("invalid context type"),
+    };
+
+    // If necessary, turn a void context into something we can safely ptrCast
+    const safe_context: *anyopaque = if (ContextT == void) @ptrCast(@constCast(&{})) else ctx;
+
+    const channel = v8.InspectorChannel.init(safe_context, InspectorContainer.onInspectorResponse, InspectorContainer.onInspectorEvent, isolate);
+
+    const client = v8.InspectorClient.init();
+
+    const inner = try allocator.create(v8.Inspector);
+    v8.Inspector.init(inner, client, channel, isolate);
+    return .{ .inner = inner, .isolate = isolate, .session = inner.connect() };
+}
+
+pub fn deinit(self: *const Inspector) void {
+    self.session.deinit();
+    self.inner.deinit();
+}
+
+pub fn send(self: *const Inspector, msg: []const u8) void {
+    // Can't assume the main Context exists (with its HandleScope)
+    // available when doing this. Pages (and thus the HandleScope)
+    // comes and goes, but CDP can keep sending messages.
+    const isolate = self.isolate;
+    var temp_scope: v8.HandleScope = undefined;
+    v8.HandleScope.init(&temp_scope, isolate);
+    defer temp_scope.deinit();
+
+    self.session.dispatchProtocolMessage(isolate, msg);
+}
+
+// From CDP docs
+// https://chromedevtools.github.io/devtools-protocol/tot/Runtime/#type-ExecutionContextDescription
+// ----
+// - name: Human readable name describing given context.
+// - origin: Execution context origin (ie. URL who initialised the request)
+// - auxData: Embedder-specific auxiliary data likely matching
+// {isDefault: boolean, type: 'default'|'isolated'|'worker', frameId: string}
+// - is_default_context: Whether the execution context is default, should match the auxData
+pub fn contextCreated(
+    self: *const Inspector,
+    context: *const Context,
+    name: []const u8,
+    origin: []const u8,
+    aux_data: ?[]const u8,
+    is_default_context: bool,
+) void {
+    self.inner.contextCreated(context.v8_context, name, origin, aux_data, is_default_context);
+}
+
+// Retrieves the RemoteObject for a given value.
+// The value is loaded through the ExecutionWorld's mapZigInstanceToJs function,
+// just like a method return value. Therefore, if we've mapped this
+// value before, we'll get the existing JS PersistedObject and if not
+// we'll create it and track it for cleanup when the context ends.
+pub fn getRemoteObject(
+    self: *const Inspector,
+    context: *Context,
+    group: []const u8,
+    value: anytype,
+) !RemoteObject {
+    const js_value = try context.zigValueToJs(value);
+
+    // We do not want to expose this as a parameter for now
+    const generate_preview = false;
+    return self.session.wrapObject(
+        context.isolate,
+        context.v8_context,
+        js_value,
+        group,
+        generate_preview,
+    );
+}
+
+// Gets a value by object ID regardless of which context it is in.
+pub fn getNodePtr(self: *const Inspector, allocator: Allocator, object_id: []const u8) !?*anyopaque {
+    const unwrapped = try self.session.unwrapObject(allocator, object_id);
+    // The values context and groupId are not used here
+    const toa = getTaggedAnyOpaque(unwrapped.value) orelse return null;
+    if (toa.subtype == null or toa.subtype != .node) return error.ObjectIdIsNotANode;
+    return toa.ptr;
+}
+
+const NoopInspector = struct {
+    pub fn onInspectorResponse(_: *anyopaque, _: u32, _: []const u8) void {}
+    pub fn onInspectorEvent(_: *anyopaque, _: []const u8) void {}
+};
+
+pub fn getTaggedAnyOpaque(value: v8.Value) ?*js.TaggedAnyOpaque {
+    if (value.isObject() == false) {
+        return null;
+    }
+    const obj = value.castTo(v8.Object);
+    if (obj.internalFieldCount() == 0) {
+        return null;
+    }
+
+    const external_data = obj.getInternalField(0).castTo(v8.External).get().?;
+    return @ptrCast(@alignCast(external_data));
+}

src/browser/js/Object.zig

@@ -0,0 +1,149 @@
+const std = @import("std");
+const js = @import("js.zig");
+const v8 = js.v8;
+
+const Caller = @import("Caller.zig");
+const Context = @import("Context.zig");
+const PersistentObject = v8.Persistent(v8.Object);
+
+const Allocator = std.mem.Allocator;
+
+const Object = @This();
+js_obj: v8.Object,
+context: *js.Context,
+
+pub const SetOpts = packed struct(u32) {
+    READ_ONLY: bool = false,
+    DONT_ENUM: bool = false,
+    DONT_DELETE: bool = false,
+    _: u29 = 0,
+};
+pub fn setIndex(self: Object, index: u32, value: anytype, opts: SetOpts) !void {
+    @setEvalBranchQuota(10000);
+    const key = switch (index) {
+        inline 0...20 => |i| std.fmt.comptimePrint("{d}", .{i}),
+        else => try std.fmt.allocPrint(self.context.arena, "{d}", .{index}),
+    };
+    return self.set(key, value, opts);
+}
+
+pub fn set(self: Object, key: []const u8, value: anytype, opts: SetOpts) error{ FailedToSet, OutOfMemory }!void {
+    const context = self.context;
+
+    const js_key = v8.String.initUtf8(context.isolate, key);
+    const js_value = try context.zigValueToJs(value);
+
+    const res = self.js_obj.defineOwnProperty(context.v8_context, js_key.toName(), js_value, @bitCast(opts)) orelse false;
+    if (!res) {
+        return error.FailedToSet;
+    }
+}
+
+pub fn get(self: Object, key: []const u8) !js.Value {
+    const context = self.context;
+    const js_key = v8.String.initUtf8(context.isolate, key);
+    const js_val = try self.js_obj.getValue(context.v8_context, js_key);
+    return context.createValue(js_val);
+}
+
+pub fn isTruthy(self: Object) bool {
+    const js_value = self.js_obj.toValue();
+    return js_value.toBool(self.context.isolate);
+}
+
+pub fn toString(self: Object) ![]const u8 {
+    const js_value = self.js_obj.toValue();
+    return self.context.valueToString(js_value, .{});
+}
+
+pub fn toDetailString(self: Object) ![]const u8 {
+    const js_value = self.js_obj.toValue();
+    return self.context.valueToDetailString(js_value);
+}
+
+pub fn format(self: Object, comptime _: []const u8, _: std.fmt.FormatOptions, writer: anytype) !void {
+    return writer.writeAll(try self.toString());
+}
+
+pub fn toJson(self: Object, allocator: Allocator) ![]u8 {
+    const json_string = try v8.Json.stringify(self.context.v8_context, self.js_obj.toValue(), null);
+    const str = try self.context.jsStringToZig(json_string, .{ .allocator = allocator });
+    return str;
+}
+
+pub fn persist(self: Object) !Object {
+    var context = self.context;
+    const js_obj = self.js_obj;
+
+    const persisted = PersistentObject.init(context.isolate, js_obj);
+    try context.js_object_list.append(context.arena, persisted);
+
+    return .{
+        .context = context,
+        .js_obj = persisted.castToObject(),
+    };
+}
+
+pub fn getFunction(self: Object, name: []const u8) !?js.Function {
+    if (self.isNullOrUndefined()) {
+        return null;
+    }
+    const context = self.context;
+
+    const js_name = v8.String.initUtf8(context.isolate, name);
+
+    const js_value = try self.js_obj.getValue(context.v8_context, js_name.toName());
+    if (!js_value.isFunction()) {
+        return null;
+    }
+    return try context.createFunction(js_value);
+}
+
+pub fn isNull(self: Object) bool {
+    return self.js_obj.toValue().isNull();
+}
+
+pub fn isUndefined(self: Object) bool {
+    return self.js_obj.toValue().isUndefined();
+}
+
+pub fn triState(self: Object, comptime Struct: type, comptime name: []const u8, comptime T: type) !TriState(T) {
+    if (self.isNull()) {
+        return .{ .null = {} };
+    }
+    if (self.isUndefined()) {
+        return .{ .undefined = {} };
+    }
+    return .{ .value = try self.toZig(Struct, name, T) };
+}
+
+pub fn isNullOrUndefined(self: Object) bool {
+    return self.js_obj.toValue().isNullOrUndefined();
+}
+
+pub fn nameIterator(self: Object) js.ValueIterator {
+    const context = self.context;
+    const js_obj = self.js_obj;
+
+    const array = js_obj.getPropertyNames(context.v8_context);
+    const count = array.length();
+
+    return .{
+        .count = count,
+        .context = context,
+        .js_obj = array.castTo(v8.Object),
+    };
+}
+
+pub fn toZig(self: Object, comptime Struct: type, comptime name: []const u8, comptime T: type) !T {
+    const named_function = comptime Caller.NamedFunction.init(Struct, name);
+    return self.context.jsValueToZig(named_function, T, self.js_obj.toValue());
+}
+
+pub fn TriState(comptime T: type) type {
+    return union(enum) {
+        null: void,
+        undefined: void,
+        value: T,
+    };
+}

src/browser/js/Platform.zig

@@ -0,0 +1,21 @@
+const js = @import("js.zig");
+const v8 = js.v8;
+
+const Platform = @This();
+inner: v8.Platform,
+
+pub fn init() !Platform {
+    if (v8.initV8ICU() == false) {
+        return error.FailedToInitializeICU;
+    }
+    const platform = v8.Platform.initDefault(0, true);
+    v8.initV8Platform(platform);
+    v8.initV8();
+    return .{ .inner = platform };
+}
+
+pub fn deinit(self: Platform) void {
+    _ = v8.deinitV8();
+    v8.deinitV8Platform();
+    self.inner.deinit();
+}

src/browser/js/This.zig

@@ -0,0 +1,25 @@
+const std = @import("std");
+const js = @import("js.zig");
+const v8 = js.v8;
+
+const Allocator = std.mem.Allocator;
+
+// This only exists so that we know whether a function wants the opaque
+// JS argument (js.Object), or if it wants the receiver as an opaque
+// value.
+// js.Object is normally used when a method wants an opaque JS object
+// that it'll pass into a callback.
+// This is used when the function wants to do advanced manipulation
+// of the v8.Object bound to the instance. For example, postAttach is an
+// example of using This.
+
+const This = @This();
+obj: js.Object,
+
+pub fn setIndex(self: This, index: u32, value: anytype, opts: js.Object.SetOpts) !void {
+    return self.obj.setIndex(index, value, opts);
+}
+
+pub fn set(self: This, key: []const u8, value: anytype, opts: js.Object.SetOpts) !void {
+    return self.obj.set(key, value, opts);
+}

src/browser/js/TryCatch.zig

@@ -0,0 +1,64 @@
+const std = @import("std");
+const js = @import("js.zig");
+const v8 = js.v8;
+
+const Allocator = std.mem.Allocator;
+
+const TryCatch = @This();
+
+inner: v8.TryCatch,
+context: *const js.Context,
+
+pub fn init(self: *TryCatch, context: *const js.Context) void {
+    self.context = context;
+    self.inner.init(context.isolate);
+}
+
+pub fn hasCaught(self: TryCatch) bool {
+    return self.inner.hasCaught();
+}
+
+// the caller needs to deinit the string returned
+pub fn exception(self: TryCatch, allocator: Allocator) !?[]const u8 {
+    const msg = self.inner.getException() orelse return null;
+    return try self.context.valueToString(msg, .{ .allocator = allocator });
+}
+
+// the caller needs to deinit the string returned
+pub fn stack(self: TryCatch, allocator: Allocator) !?[]const u8 {
+    const context = self.context;
+    const s = self.inner.getStackTrace(context.v8_context) orelse return null;
+    return try context.valueToString(s, .{ .allocator = allocator });
+}
+
+// the caller needs to deinit the string returned
+pub fn sourceLine(self: TryCatch, allocator: Allocator) !?[]const u8 {
+    const context = self.context;
+    const msg = self.inner.getMessage() orelse return null;
+    const sl = msg.getSourceLine(context.v8_context) orelse return null;
+    return try context.jsStringToZig(sl, .{ .allocator = allocator });
+}
+
+pub fn sourceLineNumber(self: TryCatch) ?u32 {
+    const context = self.context;
+    const msg = self.inner.getMessage() orelse return null;
+    return msg.getLineNumber(context.v8_context);
+}
+
+// a shorthand method to return either the entire stack message
+// or just the exception message
+// - in Debug mode return the stack if available
+// - otherwise return the exception if available
+// the caller needs to deinit the string returned
+pub fn err(self: TryCatch, allocator: Allocator) !?[]const u8 {
+    if (comptime @import("builtin").mode == .Debug) {
+        if (try self.stack(allocator)) |msg| {
+            return msg;
+        }
+    }
+    return try self.exception(allocator);
+}
+
+pub fn deinit(self: *TryCatch) void {
+    self.inner.deinit();
+}

src/browser/js/generate.zig

@@ -190,7 +190,7 @@ test "generate: Union" {
     const value = Union(.{ Astruct, Bstruct, .{Cstruct} });
     const ti = @typeInfo(value).@"union";
     try std.testing.expectEqual(3, ti.fields.len);
-    try std.testing.expectEqualStrings("*runtime.generate.test.generate: Union.Astruct.Other", @typeName(ti.fields[0].type));
+    try std.testing.expectEqualStrings("*browser.js.generate.test.generate: Union.Astruct.Other", @typeName(ti.fields[0].type));
     try std.testing.expectEqualStrings(ti.fields[0].name, "Astruct");
     try std.testing.expectEqual(*Bstruct, ti.fields[1].type);
     try std.testing.expectEqualStrings(ti.fields[1].name, "Bstruct");

src/browser/js/js.zig

@@ -0,0 +1,499 @@
+// Copyright (C) 2023-2024  Lightpanda (Selecy SAS)
+//
+// Francis Bouvier <francis@lightpanda.io>
+// Pierre Tachoire <pierre@lightpanda.io>
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as
+// published by the Free Software Foundation, either version 3 of the
+// License, or (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+const std = @import("std");
+pub const v8 = @import("v8");
+
+const types = @import("types.zig");
+const log = @import("../../log.zig");
+const Page = @import("../page.zig").Page;
+
+const Allocator = std.mem.Allocator;
+
+pub const Env = @import("Env.zig");
+pub const ExecutionWorld = @import("ExecutionWorld.zig");
+pub const Context = @import("Context.zig");
+pub const Inspector = @import("Inspector.zig");
+
+// TODO: Is "This" really necessary?
+pub const This = @import("This.zig");
+pub const Object = @import("Object.zig");
+pub const TryCatch = @import("TryCatch.zig");
+pub const Function = @import("Function.zig");
+
+const Caller = @import("Caller.zig");
+const NamedFunction = Context.NamedFunction;
+
+// If a function returns a []i32, should that map to a plain-old
+// JavaScript array, or a Int32Array? It's ambiguous. By default, we'll
+// map arrays/slices to the JavaScript arrays. If you want a TypedArray
+// wrap it in this.
+// Also, this type has nothing to do with the Env. But we place it here
+// for consistency. Want a callback? Env.Callback. Want a JsObject?
+// Env.JsObject. Want a TypedArray? Env.TypedArray.
+pub fn TypedArray(comptime T: type) type {
+    return struct {
+        pub const _TYPED_ARRAY_ID_KLUDGE = true;
+
+        values: []const T,
+
+        pub fn dupe(self: TypedArray(T), allocator: Allocator) !TypedArray(T) {
+            return .{ .values = try allocator.dupe(T, self.values) };
+        }
+    };
+}
+
+pub const PromiseResolver = struct {
+    context: *Context,
+    resolver: v8.PromiseResolver,
+
+    pub fn promise(self: PromiseResolver) Promise {
+        return self.resolver.getPromise();
+    }
+
+    pub fn resolve(self: PromiseResolver, value: anytype) !void {
+        const context = self.context;
+        const js_value = try context.zigValueToJs(value);
+
+        // resolver.resolve will return null if the promise isn't pending
+        const ok = self.resolver.resolve(context.v8_context, js_value) orelse return;
+        if (!ok) {
+            return error.FailedToResolvePromise;
+        }
+    }
+
+    pub fn reject(self: PromiseResolver, value: anytype) !void {
+        const context = self.context;
+        const js_value = try context.zigValueToJs(value);
+
+        // resolver.reject will return null if the promise isn't pending
+        const ok = self.resolver.reject(context.v8_context, js_value) orelse return;
+        if (!ok) {
+            return error.FailedToRejectPromise;
+        }
+    }
+};
+
+pub const PersistentPromiseResolver = struct {
+    context: *Context,
+    resolver: v8.Persistent(v8.PromiseResolver),
+
+    pub fn deinit(self: *PersistentPromiseResolver) void {
+        self.resolver.deinit();
+    }
+
+    pub fn promise(self: PersistentPromiseResolver) Promise {
+        return self.resolver.castToPromiseResolver().getPromise();
+    }
+
+    pub fn resolve(self: PersistentPromiseResolver, value: anytype) !void {
+        const context = self.context;
+        const js_value = try context.zigValueToJs(value);
+
+        // resolver.resolve will return null if the promise isn't pending
+        const ok = self.resolver.castToPromiseResolver().resolve(context.v8_context, js_value) orelse return;
+        if (!ok) {
+            return error.FailedToResolvePromise;
+        }
+    }
+
+    pub fn reject(self: PersistentPromiseResolver, value: anytype) !void {
+        const context = self.context;
+        const js_value = try context.zigValueToJs(value);
+
+        // resolver.reject will return null if the promise isn't pending
+        const ok = self.resolver.castToPromiseResolver().reject(context.v8_context, js_value) orelse return;
+        if (!ok) {
+            return error.FailedToRejectPromise;
+        }
+    }
+};
+
+pub const Promise = v8.Promise;
+
+// When doing jsValueToZig, string ([]const u8) are managed by the
+// call_arena. That means that if the API wants to persist the string
+// (which is relatively common), it needs to dupe it again.
+// If the parameter is an Env.String rather than a []const u8, then
+// the page's arena will be used (rather than the call arena).
+pub const String = struct {
+    string: []const u8,
+};
+
+pub const Exception = struct {
+    inner: v8.Value,
+    context: *const Context,
+
+    // the caller needs to deinit the string returned
+    pub fn exception(self: Exception, allocator: Allocator) ![]const u8 {
+        return self.context.valueToString(self.inner, .{ .allocator = allocator });
+    }
+};
+
+pub const Value = struct {
+    value: v8.Value,
+    context: *const Context,
+
+    // the caller needs to deinit the string returned
+    pub fn toString(self: Value, allocator: Allocator) ![]const u8 {
+        return self.context.valueToString(self.value, .{ .allocator = allocator });
+    }
+
+    pub fn fromJson(ctx: *Context, json: []const u8) !Value {
+        const json_string = v8.String.initUtf8(ctx.isolate, json);
+        const value = try v8.Json.parse(ctx.v8_context, json_string);
+        return Value{ .context = ctx, .value = value };
+    }
+};
+
+pub const ValueIterator = struct {
+    count: u32,
+    idx: u32 = 0,
+    js_obj: v8.Object,
+    context: *const Context,
+
+    pub fn next(self: *ValueIterator) !?Value {
+        const idx = self.idx;
+        if (idx == self.count) {
+            return null;
+        }
+        self.idx += 1;
+
+        const context = self.context;
+        const js_val = try self.js_obj.getAtIndex(context.v8_context, idx);
+        return context.createValue(js_val);
+    }
+};
+
+pub fn UndefinedOr(comptime T: type) type {
+    return union(enum) {
+        undefined: void,
+        value: T,
+    };
+}
+
+// An interface for types that want to have their jsScopeEnd function be
+// called when the call context ends
+const CallScopeEndCallback = struct {
+    ptr: *anyopaque,
+    callScopeEndFn: *const fn (ptr: *anyopaque) void,
+
+    fn init(ptr: anytype) CallScopeEndCallback {
+        const T = @TypeOf(ptr);
+        const ptr_info = @typeInfo(T);
+
+        const gen = struct {
+            pub fn callScopeEnd(pointer: *anyopaque) void {
+                const self: T = @ptrCast(@alignCast(pointer));
+                return ptr_info.pointer.child.jsCallScopeEnd(self);
+            }
+        };
+
+        return .{
+            .ptr = ptr,
+            .callScopeEndFn = gen.callScopeEnd,
+        };
+    }
+
+    pub fn callScopeEnd(self: CallScopeEndCallback) void {
+        self.callScopeEndFn(self.ptr);
+    }
+};
+
+// Callback called on global's property missing.
+// Return true to intercept the execution or false to let the call
+// continue the chain.
+pub const GlobalMissingCallback = struct {
+    ptr: *anyopaque,
+    missingFn: *const fn (ptr: *anyopaque, name: []const u8, ctx: *Context) bool,
+
+    pub fn init(ptr: anytype) GlobalMissingCallback {
+        const T = @TypeOf(ptr);
+        const ptr_info = @typeInfo(T);
+
+        const gen = struct {
+            pub fn missing(pointer: *anyopaque, name: []const u8, ctx: *Context) bool {
+                const self: T = @ptrCast(@alignCast(pointer));
+                return ptr_info.pointer.child.missing(self, name, ctx);
+            }
+        };
+
+        return .{
+            .ptr = ptr,
+            .missingFn = gen.missing,
+        };
+    }
+
+    pub fn missing(self: GlobalMissingCallback, name: []const u8, ctx: *Context) bool {
+        return self.missingFn(self.ptr, name, ctx);
+    }
+};
+
+// Attributes that return a primitive type are setup directly on the
+// FunctionTemplate when the Env is setup. More complex types need a v8.Context
+// and cannot be set directly on the FunctionTemplate.
+// We default to saying types are primitives because that's mostly what
+// we have. If we add a new complex type that isn't explictly handled here,
+// we'll get a compiler error in simpleZigValueToJs, and can then explicitly
+// add the type here.
+pub fn isComplexAttributeType(ti: std.builtin.Type) bool {
+    return switch (ti) {
+        .array => true,
+        else => false,
+    };
+}
+
+// These are simple types that we can convert to JS with only an isolate. This
+// is separated from the Caller's zigValueToJs to make it available when we
+// don't have a caller (i.e., when setting static attributes on types)
+pub fn simpleZigValueToJs(isolate: v8.Isolate, value: anytype, comptime fail: bool) if (fail) v8.Value else ?v8.Value {
+    switch (@typeInfo(@TypeOf(value))) {
+        .void => return v8.initUndefined(isolate).toValue(),
+        .null => return v8.initNull(isolate).toValue(),
+        .bool => return v8.getValue(if (value) v8.initTrue(isolate) else v8.initFalse(isolate)),
+        .int => |n| switch (n.signedness) {
+            .signed => {
+                if (value >= -2_147_483_648 and value <= 2_147_483_647) {
+                    return v8.Integer.initI32(isolate, @intCast(value)).toValue();
+                }
+                if (comptime n.bits <= 64) {
+                    return v8.getValue(v8.BigInt.initI64(isolate, @intCast(value)));
+                }
+                @compileError(@typeName(value) ++ " is not supported");
+            },
+            .unsigned => {
+                if (value <= 4_294_967_295) {
+                    return v8.Integer.initU32(isolate, @intCast(value)).toValue();
+                }
+                if (comptime n.bits <= 64) {
+                    return v8.getValue(v8.BigInt.initU64(isolate, @intCast(value)));
+                }
+                @compileError(@typeName(value) ++ " is not supported");
+            },
+        },
+        .comptime_int => {
+            if (value >= 0) {
+                if (value <= 4_294_967_295) {
+                    return v8.Integer.initU32(isolate, @intCast(value)).toValue();
+                }
+                return v8.BigInt.initU64(isolate, @intCast(value)).toValue();
+            }
+            if (value >= -2_147_483_648) {
+                return v8.Integer.initI32(isolate, @intCast(value)).toValue();
+            }
+            return v8.BigInt.initI64(isolate, @intCast(value)).toValue();
+        },
+        .comptime_float => return v8.Number.init(isolate, value).toValue(),
+        .float => |f| switch (f.bits) {
+            64 => return v8.Number.init(isolate, value).toValue(),
+            32 => return v8.Number.init(isolate, @floatCast(value)).toValue(),
+            else => @compileError(@typeName(value) ++ " is not supported"),
+        },
+        .pointer => |ptr| {
+            if (ptr.size == .slice and ptr.child == u8) {
+                return v8.String.initUtf8(isolate, value).toValue();
+            }
+            if (ptr.size == .one) {
+                const one_info = @typeInfo(ptr.child);
+                if (one_info == .array and one_info.array.child == u8) {
+                    return v8.String.initUtf8(isolate, value).toValue();
+                }
+            }
+        },
+        .array => return simpleZigValueToJs(isolate, &value, fail),
+        .optional => {
+            if (value) |v| {
+                return simpleZigValueToJs(isolate, v, fail);
+            }
+            return v8.initNull(isolate).toValue();
+        },
+        .@"struct" => {
+            const T = @TypeOf(value);
+            if (@hasDecl(T, "_TYPED_ARRAY_ID_KLUDGE")) {
+                const values = value.values;
+                const value_type = @typeInfo(@TypeOf(values)).pointer.child;
+                const len = values.len;
+                const bits = switch (@typeInfo(value_type)) {
+                    .int => |n| n.bits,
+                    .float => |f| f.bits,
+                    else => @compileError("Invalid TypeArray type: " ++ @typeName(value_type)),
+                };
+
+                var array_buffer: v8.ArrayBuffer = undefined;
+                if (len == 0) {
+                    array_buffer = v8.ArrayBuffer.init(isolate, 0);
+                } else {
+                    const buffer_len = len * bits / 8;
+                    const backing_store = v8.BackingStore.init(isolate, buffer_len);
+                    const data: [*]u8 = @ptrCast(@alignCast(backing_store.getData()));
+                    @memcpy(data[0..buffer_len], @as([]const u8, @ptrCast(values))[0..buffer_len]);
+                    array_buffer = v8.ArrayBuffer.initWithBackingStore(isolate, &backing_store.toSharedPtr());
+                }
+
+                switch (@typeInfo(value_type)) {
+                    .int => |n| switch (n.signedness) {
+                        .unsigned => switch (n.bits) {
+                            8 => return v8.Uint8Array.init(array_buffer, 0, len).toValue(),
+                            16 => return v8.Uint16Array.init(array_buffer, 0, len).toValue(),
+                            32 => return v8.Uint32Array.init(array_buffer, 0, len).toValue(),
+                            64 => return v8.BigUint64Array.init(array_buffer, 0, len).toValue(),
+                            else => {},
+                        },
+                        .signed => switch (n.bits) {
+                            8 => return v8.Int8Array.init(array_buffer, 0, len).toValue(),
+                            16 => return v8.Int16Array.init(array_buffer, 0, len).toValue(),
+                            32 => return v8.Int32Array.init(array_buffer, 0, len).toValue(),
+                            64 => return v8.BigInt64Array.init(array_buffer, 0, len).toValue(),
+                            else => {},
+                        },
+                    },
+                    .float => |f| switch (f.bits) {
+                        32 => return v8.Float32Array.init(array_buffer, 0, len).toValue(),
+                        64 => return v8.Float64Array.init(array_buffer, 0, len).toValue(),
+                        else => {},
+                    },
+                    else => {},
+                }
+                // We normally don't fail in this function unless fail == true
+                // but this can never be valid.
+                @compileError("Invalid TypeArray type: " ++ @typeName(value_type));
+            }
+        },
+        .@"union" => return simpleZigValueToJs(isolate, std.meta.activeTag(value), fail),
+        .@"enum" => {
+            const T = @TypeOf(value);
+            if (@hasDecl(T, "toString")) {
+                return simpleZigValueToJs(isolate, value.toString(), fail);
+            }
+        },
+        else => {},
+    }
+    if (fail) {
+        @compileError("Unsupported Zig type " ++ @typeName(@TypeOf(value)));
+    }
+    return null;
+}
+
+pub fn _createException(isolate: v8.Isolate, msg: []const u8) v8.Value {
+    return v8.Exception.initError(v8.String.initUtf8(isolate, msg));
+}
+
+pub fn classNameForStruct(comptime Struct: type) []const u8 {
+    if (@hasDecl(Struct, "js_name")) {
+        return Struct.js_name;
+    }
+    @setEvalBranchQuota(10_000);
+    const full_name = @typeName(Struct);
+    const last = std.mem.lastIndexOfScalar(u8, full_name, '.') orelse return full_name;
+    return full_name[last + 1 ..];
+}
+
+// When we return a Zig object to V8, we put it on the heap and pass it into
+// v8 as an *anyopaque (i.e. void *). When V8 gives us back the value, say, as a
+// function parameter, we know what type it _should_ be. Above, in Caller.method
+// (for example), we know all the parameter types. So if a Zig function takes
+// a single parameter (its receiver), we know what that type is.
+//
+// In a simple/perfect world, we could use this knowledge to cast the *anyopaque
+// to the parameter type:
+//   const arg: @typeInfo(@TypeOf(function)).@"fn".params[0] = @ptrCast(v8_data);
+//
+// But there are 2 reasons we can't do that.
+//
+// == Reason 1 ==
+// The JS code might pass the wrong type:
+//
+//   var cat = new Cat();
+//   cat.setOwner(new Cat());
+//
+// The zig _setOwner method expects the 2nd parameter to be an *Owner, but
+// the JS code passed a *Cat.
+//
+// To solve this issue, we tag every returned value so that we can check what
+// type it is. In the above case, we'd expect an *Owner, but the tag would tell
+// us that we got a *Cat. We use the type index in our Types lookup as the tag.
+//
+// == Reason 2 ==
+// Because of prototype inheritance, even "correct" code can be a challenge. For
+// example, say the above JavaScript is fixed:
+//
+//   var cat = new Cat();
+//   cat.setOwner(new Owner("Leto"));
+//
+// The issue is that setOwner might not expect an *Owner, but rather a
+// *Person, which is the prototype for Owner. Now our Zig code is expecting
+// a *Person, but it was (correctly) given an *Owner.
+// For this reason, we also store the prototype's type index.
+//
+// One of the prototype mechanisms that we support is via composition. Owner
+// can have a "proto: *Person" field. For this reason, we also store the offset
+// of the proto field, so that, given an intFromPtr(*Owner) we can access its
+// proto field.
+//
+// The other prototype mechanism that we support is for netsurf, where we just
+// cast one type to another. In this case, we'll store an offset of -1 (as a
+// sentinel to indicate that we should just cast directly).
+pub const TaggedAnyOpaque = struct {
+    // The type of object this is. The type is captured as an index, which
+    // corresponds to both a field in TYPE_LOOKUP and the index of
+    // PROTOTYPE_TABLE
+    index: u16,
+
+    // Ptr to the Zig instance. Between the context where it's called (i.e.
+    // we have the comptime parameter info for all functions), and the index field
+    // we can figure out what type this is.
+    ptr: *anyopaque,
+
+    // When we're asked to describe an object via the Inspector, we _must_ include
+    // the proper subtype (and description) fields in the returned JSON.
+    // V8 will give us a Value and ask us for the subtype. From the v8.Value we
+    // can get a v8.Object, and from the v8.Object, we can get out TaggedAnyOpaque
+    // which is where we store the subtype.
+    subtype: ?types.Sub,
+};
+
+// These are here, and not in Inspector.zig, because Inspector.zig isn't always
+// included (e.g. in the wpt build).
+
+// This is called from V8. Whenever the v8 inspector has to describe a value
+// it'll call this function to gets its [optional] subtype - which, from V8's
+// point of view, is an arbitrary string.
+pub export fn v8_inspector__Client__IMPL__valueSubtype(
+    _: *v8.c.InspectorClientImpl,
+    c_value: *const v8.C_Value,
+) callconv(.c) [*c]const u8 {
+    const external_entry = Inspector.getTaggedAnyOpaque(.{ .handle = c_value }) orelse return null;
+    return if (external_entry.subtype) |st| @tagName(st) else null;
+}
+
+// Same as valueSubType above, but for the optional description field.
+// From what I can tell, some drivers _need_ the description field to be
+// present, even if it's empty. So if we have a subType for the value, we'll
+// put an empty description.
+pub export fn v8_inspector__Client__IMPL__descriptionForValueSubtype(
+    _: *v8.c.InspectorClientImpl,
+    v8_context: *const v8.C_Context,
+    c_value: *const v8.C_Value,
+) callconv(.c) [*c]const u8 {
+    _ = v8_context;
+
+    // We _must_ include a non-null description in order for the subtype value
+    // to be included. Besides that, I don't know if the value has any meaning
+    const external_entry = Inspector.getTaggedAnyOpaque(.{ .handle = c_value }) orelse return null;
+    return if (external_entry.subtype == null) null else "";
+}

src/browser/js/types.zig

@@ -0,0 +1,183 @@
+const std = @import("std");
+
+const generate = @import("generate.zig");
+
+const Interfaces = generate.Tuple(.{
+    @import("../crypto/crypto.zig").Crypto,
+    @import("../console/console.zig").Console,
+    @import("../css/css.zig").Interfaces,
+    @import("../cssom/cssom.zig").Interfaces,
+    @import("../dom/dom.zig").Interfaces,
+    @import("../dom/shadow_root.zig").ShadowRoot,
+    @import("../encoding/encoding.zig").Interfaces,
+    @import("../events/event.zig").Interfaces,
+    @import("../html/html.zig").Interfaces,
+    @import("../iterator/iterator.zig").Interfaces,
+    @import("../storage/storage.zig").Interfaces,
+    @import("../url/url.zig").Interfaces,
+    @import("../xhr/xhr.zig").Interfaces,
+    @import("../xhr/form_data.zig").Interfaces,
+    @import("../xhr/File.zig"),
+    @import("../xmlserializer/xmlserializer.zig").Interfaces,
+    @import("../fetch/fetch.zig").Interfaces,
+    @import("../streams/streams.zig").Interfaces,
+});
+
+pub const Types = @typeInfo(Interfaces).@"struct".fields;
+
+// Imagine we have a type Cat which has a getter:
+//
+//    fn get_owner(self: *Cat) *Owner {
+//        return self.owner;
+//    }
+//
+// When we execute caller.getter, we'll end up doing something like:
+//   const res = @call(.auto, Cat.get_owner, .{cat_instance});
+//
+// How do we turn `res`, which is an *Owner, into something we can return
+// to v8? We need the ObjectTemplate associated with Owner. How do we
+// get that? Well, we store all the ObjectTemplates in an array that's
+// tied to env. So we do something like:
+//
+//    env.templates[index_of_owner].initInstance(...);
+//
+// But how do we get that `index_of_owner`? `Lookup` is a struct
+// that looks like:
+//
+// const Lookup = struct {
+//     comptime cat: usize = 0,
+//     comptime owner: usize = 1,
+//     ...
+// }
+//
+// So to get the template index of `owner`, we can do:
+//
+//  const index_id = @field(type_lookup, @typeName(@TypeOf(res));
+//
+pub const Lookup = blk: {
+    var fields: [Types.len]std.builtin.Type.StructField = undefined;
+    for (Types, 0..) |s, i| {
+
+        // This prototype type check has nothing to do with building our
+        // Lookup. But we put it here, early, so that the rest of the
+        // code doesn't have to worry about checking if Struct.prototype is
+        // a pointer.
+        const Struct = s.defaultValue().?;
+        if (@hasDecl(Struct, "prototype") and @typeInfo(Struct.prototype) != .pointer) {
+            @compileError(std.fmt.comptimePrint("Prototype '{s}' for type '{s} must be a pointer", .{ @typeName(Struct.prototype), @typeName(Struct) }));
+        }
+
+        fields[i] = .{
+            .name = @typeName(Receiver(Struct)),
+            .type = usize,
+            .is_comptime = true,
+            .alignment = @alignOf(usize),
+            .default_value_ptr = &i,
+        };
+    }
+    break :blk @Type(.{ .@"struct" = .{
+        .layout = .auto,
+        .decls = &.{},
+        .is_tuple = false,
+        .fields = &fields,
+    } });
+};
+
+pub const LOOKUP = Lookup{};
+
+// Creates a list where the index of a type contains its prototype index
+//   const Animal = struct{};
+//   const Cat = struct{
+//       pub const prototype = *Animal;
+// };
+//
+// Would create an array: [0, 0]
+// Animal, at index, 0, has no prototype, so we set it to itself
+// Cat, at index 1, has an Animal prototype, so we set it to 0.
+//
+// When we're trying to pass an argument to a Zig function, we'll know the
+// target type (the function parameter type), and we'll have a
+// TaggedAnyOpaque which will have the index of the type of that parameter.
+// We'll use the PROTOTYPE_TABLE to see if the TaggedAnyType should be
+// cast to a prototype.
+pub const PROTOTYPE_TABLE = blk: {
+    var table: [Types.len]u16 = undefined;
+    for (Types, 0..) |s, i| {
+        var prototype_index = i;
+        const Struct = s.defaultValue().?;
+        if (@hasDecl(Struct, "prototype")) {
+            const TI = @typeInfo(Struct.prototype);
+            const proto_name = @typeName(Receiver(TI.pointer.child));
+            prototype_index = @field(LOOKUP, proto_name);
+        }
+        table[i] = prototype_index;
+    }
+    break :blk table;
+};
+
+// This is essentially meta data for each type. Each is stored in env.meta_lookup
+// The index for a type can be retrieved via:
+//   const index = @field(TYPE_LOOKUP, @typeName(Receiver(Struct)));
+//   const meta = env.meta_lookup[index];
+pub const Meta = struct {
+    // Every type is given a unique index. That index is used to lookup various
+    // things, i.e. the prototype chain.
+    index: u16,
+
+    // We store the type's subtype here, so that when we create an instance of
+    // the type, and bind it to JavaScript, we can store the subtype along with
+    // the created TaggedAnyOpaque.s
+    subtype: ?Sub,
+
+    // If this type has composition-based prototype, represents the byte-offset
+    // from ptr where the `proto` field is located. A negative offsets is used
+    // to indicate that the prototype field is behind a pointer.
+    proto_offset: i32,
+};
+
+pub const Sub = enum {
+    @"error",
+    array,
+    arraybuffer,
+    dataview,
+    date,
+    generator,
+    iterator,
+    map,
+    node,
+    promise,
+    proxy,
+    regexp,
+    set,
+    typedarray,
+    wasmvalue,
+    weakmap,
+    weakset,
+    webassemblymemory,
+};
+
+// When we map a Zig instance into a JsObject, we'll normally store the a
+// TaggedAnyOpaque (TAO) inside of the JsObject's internal field. This requires
+// ensuring that the instance template has an InternalFieldCount of 1. However,
+// for empty objects, we don't need to store the TAO, because we can't just cast
+// one empty object to another, so for those, as an optimization, we do not set
+// the InternalFieldCount.
+pub fn isEmpty(comptime T: type) bool {
+    return @typeInfo(T) != .@"opaque" and @sizeOf(T) == 0 and @hasDecl(T, "js_legacy_factory") == false;
+}
+
+// If we have a struct:
+// const Cat = struct {
+//    pub fn meow(self: *Cat) void { ... }
+// }
+// Then obviously, the receiver of its methods are going to be a *Cat (or *const Cat)
+//
+// However, we can also do:
+// const Cat = struct {
+//    pub const Self = OtherImpl;
+//    pub fn meow(self: *OtherImpl) void { ... }
+// }
+// In which case, as we see above, the receiver is derived from the Self declaration
+pub fn Receiver(comptime Struct: type) type {
+    return if (@hasDecl(Struct, "Self")) Struct.Self else Struct;
+}

src/browser/mimalloc.zig

@@ -26,14 +26,9 @@ const c = @cImport({
     @cInclude("mimalloc.h");
 });
 
-const Error = error{
-    HeapNotNull,
-    HeapNull,
-};
-
 var heap: ?*c.mi_heap_t = null;
 
-pub fn create() Error!void {
+pub fn create() void {
     std.debug.assert(heap == null);
     heap = c.mi_heap_new();
     std.debug.assert(heap != null);
@@ -45,6 +40,45 @@ pub fn destroy() void {
     heap = null;
 }
 
+pub fn getRSS() i64 {
+    if (@import("builtin").mode != .Debug) {
+        // just don't trust my implementation, plus a caller might not know
+        // that this requires parsing some unstructured data
+        @compileError("Only available in debug builds");
+    }
+    var buf: [1024 * 8]u8 = undefined;
+    var fba = std.heap.FixedBufferAllocator.init(&buf);
+    var writer = std.Io.Writer.Allocating.init(fba.allocator());
+
+    c.mi_stats_print_out(struct {
+        fn print(msg: [*c]const u8, data: ?*anyopaque) callconv(.c) void {
+            const w: *std.Io.Writer = @ptrCast(@alignCast(data.?));
+            w.writeAll(std.mem.span(msg)) catch |err| {
+                std.debug.print("Failed to write mimalloc data: {}\n", .{err});
+            };
+        }
+    }.print, &writer.writer);
+
+    const data = writer.written();
+    const index = std.mem.indexOf(u8, data, "rss: ") orelse return -1;
+    const sep = std.mem.indexOfScalarPos(u8, data, index + 5, ' ') orelse return -2;
+    const value = std.fmt.parseFloat(f64, data[index + 5 .. sep]) catch return -3;
+    const unit = data[sep + 1 ..];
+    if (std.mem.startsWith(u8, unit, "KiB,")) {
+        return @as(i64, @intFromFloat(value)) * 1024;
+    }
+
+    if (std.mem.startsWith(u8, unit, "MiB,")) {
+        return @as(i64, @intFromFloat(value)) * 1024 * 1024;
+    }
+
+    if (std.mem.startsWith(u8, unit, "GiB,")) {
+        return @as(i64, @intFromFloat(value)) * 1024 * 1024 * 1024;
+    }
+
+    return -4;
+}
+
 pub export fn m_alloc(size: usize) callconv(.c) ?*anyopaque {
     std.debug.assert(heap != null);
     return c.mi_heap_malloc(heap.?, size);

src/browser/mime.zig

@@ -17,7 +17,6 @@
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 const std = @import("std");
-const Allocator = std.mem.Allocator;
 
 pub const Mime = struct {
     content_type: ContentType,
@@ -55,7 +54,7 @@ pub const Mime = struct {
     };
 
     /// Returns the null-terminated charset value.
-    pub inline fn charsetString(mime: *const Mime) [:0]const u8 {
+    pub fn charsetString(mime: *const Mime) [:0]const u8 {
         return @ptrCast(&mime.charset);
     }
 

src/browser/netsurf.zig

@@ -36,8 +36,8 @@ const mimalloc = @import("mimalloc.zig");
 // init initializes netsurf lib.
 // init starts a mimalloc heap arena for the netsurf session. The caller must
 // call deinit() to free the arena memory.
-pub fn init() !void {
-    try mimalloc.create();
+pub fn init() void {
+    mimalloc.create();
 }
 
 // deinit frees the mimalloc heap arena memory.
@@ -84,7 +84,7 @@ pub fn deinit() void {
 // - VtableT: the type of the vtable (dom_node_vtable, dom_element_vtable, etc)
 // - NodeT: the type of the node interface (dom_element, dom_document, etc)
 // - node: the node interface instance
-inline fn getVtable(comptime VtableT: type, comptime NodeT: type, node: anytype) VtableT {
+fn getVtable(comptime VtableT: type, comptime NodeT: type, node: anytype) VtableT {
     // first align correctly the node interface
     const node_aligned: *align(@alignOf(NodeExternal)) NodeT = @alignCast(node);
     // then convert the node interface to a base node
@@ -101,12 +101,12 @@ inline fn getVtable(comptime VtableT: type, comptime NodeT: type, node: anytype)
 // Utils
 const String = c.dom_string;
 
-inline fn strToData(s: *String) []const u8 {
+fn strToData(s: *String) []const u8 {
     const data = c.dom_string_data(s);
     return data[0..c.dom_string_byte_length(s)];
 }
 
-pub inline fn strFromData(data: []const u8) !*String {
+pub fn strFromData(data: []const u8) !*String {
     var s: ?*String = null;
     const err = c.dom_string_create(data.ptr, data.len, &s);
     try DOMErr(err);
@@ -116,10 +116,10 @@ pub inline fn strFromData(data: []const u8) !*String {
 const LWCString = c.lwc_string;
 
 // TODO implement lwcStringToData
-// inline fn lwcStringToData(s: *LWCString) []const u8 {
+// fn lwcStringToData(s: *LWCString) []const u8 {
 // }
 
-inline fn lwcStringFromData(data: []const u8) !*LWCString {
+fn lwcStringFromData(data: []const u8) !*LWCString {
     var s: ?*LWCString = null;
     const err = c.lwc_intern_string(data.ptr, data.len, &s);
     try DOMErr(err);
@@ -445,13 +445,15 @@ pub fn eventInit(evt: *Event, typ: []const u8, opts: EventInit) !void {
     try DOMErr(err);
 }
 
-pub fn eventType(evt: *Event) ![]const u8 {
+pub fn eventType(evt: *Event) []const u8 {
     var s: ?*String = null;
     const err = c._dom_event_get_type(evt, &s);
-    try DOMErr(err);
+    std.debug.assert(err == c.DOM_NO_ERR);
 
     // if the event type is null, return a empty string.
-    if (s == null) return "";
+    if (s == null) {
+        return "";
+    }
 
     return strToData(s.?);
 }
@@ -556,6 +558,8 @@ pub const EventType = enum(u8) {
     xhr_event = 6,
     message_event = 7,
     keyboard_event = 8,
+    pop_state = 9,
+    composition_event = 10,
 };
 
 pub const MutationEvent = c.dom_mutation_event;
@@ -571,10 +575,18 @@ pub fn mutationEventAttributeName(evt: *MutationEvent) ![]const u8 {
     return strToData(s.?);
 }
 
-pub fn mutationEventPrevValue(evt: *MutationEvent) !?[]const u8 {
+pub fn mutationEventPrevValue(evt: *MutationEvent) ?[]const u8 {
     var s: ?*String = null;
     const err = c._dom_mutation_event_get_prev_value(evt, &s);
-    try DOMErr(err);
+    std.debug.assert(err == c.DOM_NO_ERR);
+    if (s == null) return null;
+    return strToData(s.?);
+}
+
+pub fn mutationEventNewValue(evt: *MutationEvent) ?[]const u8 {
+    var s: ?*String = null;
+    const err = c._dom_mutation_event_get_new_value(evt, &s);
+    std.debug.assert(err == c.DOM_NO_ERR);
     if (s == null) return null;
     return strToData(s.?);
 }
@@ -582,7 +594,7 @@ pub fn mutationEventPrevValue(evt: *MutationEvent) !?[]const u8 {
 pub fn mutationEventRelatedNode(evt: *MutationEvent) !?*Node {
     var n: NodeExternal = undefined;
     const err = c._dom_mutation_event_get_related_node(evt, &n);
-    try DOMErr(err);
+    std.debug.assert(err == c.DOM_NO_ERR);
     if (n == null) return null;
     return @as(*Node, @ptrCast(@alignCast(n)));
 }
@@ -779,10 +791,10 @@ pub fn eventTargetDispatchEvent(et: *EventTarget, event: *Event) !bool {
     return res;
 }
 
-pub fn eventTargetInternalType(et: *EventTarget) !EventTargetTBase.InternalType {
+pub fn eventTargetInternalType(et: *EventTarget) EventTargetTBase.InternalType {
     var res: u32 = undefined;
     const err = eventTargetVtable(et).internal_type.?(et, &res);
-    try DOMErr(err);
+    std.debug.assert(err == c.DOM_NO_ERR);
     return @enumFromInt(res);
 }
 
@@ -850,10 +862,8 @@ pub const EventTargetTBase = extern struct {
     pub fn dispatch_event(et: [*c]c.dom_event_target, evt: ?*c.struct_dom_event, res: [*c]bool) callconv(.c) c.dom_exception {
         const self = @as(*Self, @ptrCast(et));
         // Set the event target to the target dispatched.
-        const e = c._dom_event_set_target(evt, et);
-        if (e != c.DOM_NO_ERR) {
-            return e;
-        }
+        const err = c._dom_event_set_target(evt, et);
+        std.debug.assert(err == c.DOM_NO_ERR);
         return c._dom_event_target_dispatch(et, &self.eti, evt, c.DOM_AT_TARGET, res);
     }
 
@@ -1046,17 +1056,17 @@ pub const NodeType = enum(u4) {
 // NodeList
 pub const NodeList = c.dom_nodelist;
 
-pub fn nodeListLength(nodeList: *NodeList) !u32 {
+pub fn nodeListLength(nodeList: *NodeList) u32 {
     var ln: u32 = undefined;
     const err = c.dom_nodelist_get_length(nodeList, &ln);
-    try DOMErr(err);
+    std.debug.assert(err == c.DOM_NO_ERR);
     return ln;
 }
 
-pub fn nodeListItem(nodeList: *NodeList, index: u32) !?*Node {
+pub fn nodeListItem(nodeList: *NodeList, index: u32) ?*Node {
     var n: NodeExternal = undefined;
     const err = c._dom_nodelist_item(nodeList, index, &n);
-    try DOMErr(err);
+    std.debug.assert(err == c.DOM_NO_ERR);
     if (n == null) return null;
     return @as(*Node, @ptrCast(@alignCast(n)));
 }
@@ -1173,88 +1183,86 @@ fn nodeVtable(node: *Node) c.dom_node_vtable {
 pub fn nodeLocalName(node: *Node) ![]const u8 {
     var s: ?*String = null;
     const err = nodeVtable(node).dom_node_get_local_name.?(node, &s);
-    try DOMErr(err);
+    std.debug.assert(err == c.DOM_NO_ERR);
     if (s == null) return "";
+
     var s_lower: ?*String = null;
     const errStr = c.dom_string_tolower(s, true, &s_lower);
     try DOMErr(errStr);
     return strToData(s_lower.?);
 }
 
-pub fn nodeType(node: *Node) !NodeType {
+pub fn nodeType(node: *Node) NodeType {
     var node_type: c.dom_node_type = undefined;
     const err = nodeVtable(node).dom_node_get_node_type.?(node, &node_type);
-    try DOMErr(err);
+    std.debug.assert(err == c.DOM_NO_ERR);
     return @as(NodeType, @enumFromInt(node_type));
 }
 
-pub fn nodeFirstChild(node: *Node) !?*Node {
+pub fn nodeFirstChild(node: *Node) ?*Node {
     var res: ?*Node = null;
     const err = nodeVtable(node).dom_node_get_first_child.?(node, &res);
-    try DOMErr(err);
+    std.debug.assert(err == c.DOM_NO_ERR);
     return res;
 }
 
-pub fn nodeLastChild(node: *Node) !?*Node {
+pub fn nodeLastChild(node: *Node) ?*Node {
     var res: ?*Node = null;
     const err = nodeVtable(node).dom_node_get_last_child.?(node, &res);
-    try DOMErr(err);
+    std.debug.assert(err == c.DOM_NO_ERR);
     return res;
 }
 
-pub fn nodeNextSibling(node: *Node) !?*Node {
+pub fn nodeNextSibling(node: *Node) ?*Node {
     var res: ?*Node = null;
     const err = nodeVtable(node).dom_node_get_next_sibling.?(node, &res);
-    try DOMErr(err);
+    std.debug.assert(err == c.DOM_NO_ERR);
     return res;
 }
 
-pub fn nodeNextElementSibling(node: *Node) !?*Element {
+pub fn nodeNextElementSibling(node: *Node) ?*Element {
     var n = node;
     while (true) {
-        const res = try nodeNextSibling(n);
-        if (res == null) return null;
+        const res = nodeNextSibling(n) orelse return null;
 
-        if (try nodeType(res.?) == .element) {
-            return @as(*Element, @ptrCast(res.?));
+        if (nodeType(res) == .element) {
+            return @as(*Element, @ptrCast(res));
         }
-        n = res.?;
+        n = res;
     }
     return null;
 }
 
-pub fn nodePreviousSibling(node: *Node) !?*Node {
+pub fn nodePreviousSibling(node: *Node) ?*Node {
     var res: ?*Node = null;
     const err = nodeVtable(node).dom_node_get_previous_sibling.?(node, &res);
-    try DOMErr(err);
+    std.debug.assert(err == c.DOM_NO_ERR);
     return res;
 }
 
-pub fn nodePreviousElementSibling(node: *Node) !?*Element {
+pub fn nodePreviousElementSibling(node: *Node) ?*Element {
     var n = node;
     while (true) {
-        const res = try nodePreviousSibling(n);
-        if (res == null) return null;
-
-        if (try nodeType(res.?) == .element) {
-            return @as(*Element, @ptrCast(res.?));
+        const res = nodePreviousSibling(n) orelse return null;
+        if (nodeType(res) == .element) {
+            return @as(*Element, @ptrCast(res));
         }
-        n = res.?;
+        n = res;
     }
     return null;
 }
 
-pub fn nodeParentNode(node: *Node) !?*Node {
+pub fn nodeParentNode(node: *Node) ?*Node {
     var res: ?*Node = null;
     const err = nodeVtable(node).dom_node_get_parent_node.?(node, &res);
-    try DOMErr(err);
+    std.debug.assert(err == c.DOM_NO_ERR);
     return res;
 }
 
-pub fn nodeParentElement(node: *Node) !?*Element {
-    const res = try nodeParentNode(node);
+pub fn nodeParentElement(node: *Node) ?*Element {
+    const res = nodeParentNode(node);
     if (res) |value| {
-        if (try nodeType(value) == .element) {
+        if (nodeType(value) == .element) {
             return @as(*Element, @ptrCast(value));
         }
     }
@@ -1269,17 +1277,17 @@ pub fn nodeName(node: *Node) ![]const u8 {
     return strToData(s.?);
 }
 
-pub fn nodeOwnerDocument(node: *Node) !?*Document {
+pub fn nodeOwnerDocument(node: *Node) ?*Document {
     var doc: ?*Document = null;
     const err = nodeVtable(node).dom_node_get_owner_document.?(node, &doc);
-    try DOMErr(err);
+    std.debug.assert(err == c.DOM_NO_ERR);
     return doc;
 }
 
-pub fn nodeValue(node: *Node) !?[]const u8 {
+pub fn nodeValue(node: *Node) ?[]const u8 {
     var s: ?*String = null;
     const err = nodeVtable(node).dom_node_get_node_value.?(node, &s);
-    try DOMErr(err);
+    std.debug.assert(err == c.DOM_NO_ERR);
     if (s == null) return null;
     return strToData(s.?);
 }
@@ -1290,14 +1298,14 @@ pub fn nodeSetValue(node: *Node, value: []const u8) !void {
     try DOMErr(err);
 }
 
-pub fn nodeTextContent(node: *Node) !?[]const u8 {
+pub fn nodeTextContent(node: *Node) ?[]const u8 {
     var s: ?*String = null;
     const err = nodeVtable(node).dom_node_get_text_content.?(node, &s);
-    try DOMErr(err);
+    std.debug.assert(err == c.DOM_NO_ERR);
     if (s == null) {
         // NOTE: it seems that there is a bug in netsurf implem
         // an empty Element should return an empty string and not null
-        if (try nodeType(node) == .element) {
+        if (nodeType(node) == .element) {
             return "";
         }
         return null;
@@ -1318,10 +1326,10 @@ pub fn nodeGetChildNodes(node: *Node) !*NodeList {
     return nlist.?;
 }
 
-pub fn nodeGetRootNode(node: *Node) !*Node {
+pub fn nodeGetRootNode(node: *Node) *Node {
     var root = node;
     while (true) {
-        const parent = try nodeParentNode(root);
+        const parent = nodeParentNode(root);
         if (parent) |parent_| {
             root = parent_;
         } else break;
@@ -1343,21 +1351,21 @@ pub fn nodeCloneNode(node: *Node, is_deep: bool) !*Node {
     return res.?;
 }
 
-pub fn nodeContains(node: *Node, other: *Node) !bool {
+pub fn nodeContains(node: *Node, other: *Node) bool {
     var res: bool = undefined;
     const err = c._dom_node_contains(node, other, &res);
-    try DOMErr(err);
+    std.debug.assert(err == c.DOM_NO_ERR);
     return res;
 }
 
-pub fn nodeHasChildNodes(node: *Node) !bool {
+pub fn nodeHasChildNodes(node: *Node) bool {
     var res: bool = undefined;
     const err = nodeVtable(node).dom_node_has_child_nodes.?(node, &res);
-    try DOMErr(err);
+    std.debug.assert(err == c.DOM_NO_ERR);
     return res;
 }
 
-pub fn nodeInsertBefore(node: *Node, new_node: *Node, ref_node: *Node) !*Node {
+pub fn nodeInsertBefore(node: *Node, new_node: *Node, ref_node: ?*Node) !*Node {
     var res: ?*Node = null;
     const err = nodeVtable(node).dom_node_insert_before.?(node, new_node, ref_node, &res);
     try DOMErr(err);
@@ -1368,7 +1376,7 @@ pub fn nodeIsDefaultNamespace(node: *Node, namespace_: ?[]const u8) !bool {
     const s = if (namespace_) |n| try strFromData(n) else null;
     var res: bool = undefined;
     const err = nodeVtable(node).dom_node_is_default_namespace.?(node, s, &res);
-    try DOMErr(err);
+    std.debug.assert(err == c.DOM_NO_ERR);
     return res;
 }
 
@@ -1379,10 +1387,10 @@ pub fn nodeIsEqualNode(node: *Node, other: *Node) !bool {
     return res;
 }
 
-pub fn nodeIsSameNode(node: *Node, other: *Node) !bool {
+pub fn nodeIsSameNode(node: *Node, other: *Node) bool {
     var res: bool = undefined;
     const err = nodeVtable(node).dom_node_is_same.?(node, other, &res);
-    try DOMErr(err);
+    std.debug.assert(err == c.DOM_NO_ERR);
     return res;
 }
 
@@ -1422,13 +1430,6 @@ pub fn nodeReplaceChild(node: *Node, new_child: *Node, old_child: *Node) !*Node
     return res.?;
 }
 
-pub fn nodeHasAttributes(node: *Node) !bool {
-    var res: bool = undefined;
-    const err = nodeVtable(node).dom_node_has_attributes.?(node, &res);
-    try DOMErr(err);
-    return res;
-}
-
 pub fn nodeGetAttributes(node: *Node) !?*NamedNodeMap {
     var res: ?*NamedNodeMap = null;
     const err = nodeVtable(node).dom_node_get_attributes.?(node, &res);
@@ -1436,18 +1437,18 @@ pub fn nodeGetAttributes(node: *Node) !?*NamedNodeMap {
     return res;
 }
 
-pub fn nodeGetNamespace(node: *Node) !?[]const u8 {
+pub fn nodeGetNamespace(node: *Node) ?[]const u8 {
     var s: ?*String = null;
     const err = nodeVtable(node).dom_node_get_namespace.?(node, &s);
-    try DOMErr(err);
+    std.debug.assert(err == c.DOM_NO_ERR);
     if (s == null) return null;
     return strToData(s.?);
 }
 
-pub fn nodeGetPrefix(node: *Node) !?[]const u8 {
+pub fn nodeGetPrefix(node: *Node) ?[]const u8 {
     var s: ?*String = null;
     const err = nodeVtable(node).dom_node_get_prefix.?(node, &s);
-    try DOMErr(err);
+    std.debug.assert(err == c.DOM_NO_ERR);
     if (s == null) return null;
     return strToData(s.?);
 }
@@ -1463,23 +1464,24 @@ pub fn nodeSetEmbedderData(node: *Node, data: *anyopaque) void {
 pub fn nodeGetElementById(node: *Node, id: []const u8) !?*Element {
     var el: ?*Element = null;
     const str_id = try strFromData(id);
-    try DOMErr(c._dom_find_element_by_id(node, str_id, &el));
+    const err = c._dom_find_element_by_id(node, str_id, &el);
+    std.debug.assert(err == c.DOM_NO_ERR);
     return el;
 }
 
 // nodeToElement is an helper to convert a node to an element.
-pub inline fn nodeToElement(node: *Node) *Element {
+pub fn nodeToElement(node: *Node) *Element {
     return @as(*Element, @ptrCast(node));
 }
 
 // nodeToDocument is an helper to convert a node to an document.
-pub inline fn nodeToDocument(node: *Node) *Document {
+pub fn nodeToDocument(node: *Node) *Document {
     return @as(*Document, @ptrCast(node));
 }
 
 // Combination of nodeToElement + elementTag
 pub fn nodeHTMLGetTagType(node: *Node) !?Tag {
-    if (try nodeType(node) != .element) {
+    if (nodeType(node) != .element) {
         return null;
     }
 
@@ -1493,14 +1495,14 @@ fn characterDataVtable(data: *CharacterData) c.dom_characterdata_vtable {
     return getVtable(c.dom_characterdata_vtable, CharacterData, data);
 }
 
-pub inline fn characterDataToNode(cdata: *CharacterData) *Node {
+pub fn characterDataToNode(cdata: *CharacterData) *Node {
     return @as(*Node, @ptrCast(@alignCast(cdata)));
 }
 
-pub fn characterDataData(cdata: *CharacterData) ![]const u8 {
+pub fn characterDataData(cdata: *CharacterData) []const u8 {
     var s: ?*String = null;
     const err = characterDataVtable(cdata).dom_characterdata_get_data.?(cdata, &s);
-    try DOMErr(err);
+    std.debug.assert(err == c.DOM_NO_ERR);
     return strToData(s.?);
 }
 
@@ -1513,7 +1515,7 @@ pub fn characterDataSetData(cdata: *CharacterData, data: []const u8) !void {
 pub fn characterDataLength(cdata: *CharacterData) !u32 {
     var n: u32 = undefined;
     const err = characterDataVtable(cdata).dom_characterdata_get_length.?(cdata, &n);
-    try DOMErr(err);
+    std.debug.assert(err == c.DOM_NO_ERR);
     return n;
 }
 
@@ -1578,7 +1580,7 @@ pub const Comment = c.dom_comment;
 pub const ProcessingInstruction = c.dom_processing_instruction;
 
 // processingInstructionToNode is an helper to convert an ProcessingInstruction to a node.
-pub inline fn processingInstructionToNode(pi: *ProcessingInstruction) *Node {
+pub fn processingInstructionToNode(pi: *ProcessingInstruction) *Node {
     return @as(*Node, @ptrCast(@alignCast(pi)));
 }
 
@@ -1633,7 +1635,7 @@ pub fn attributeGetOwnerElement(a: *Attribute) !?*Element {
 }
 
 // attributeToNode is an helper to convert an attribute to a node.
-pub inline fn attributeToNode(a: *Attribute) *Node {
+pub fn attributeToNode(a: *Attribute) *Node {
     return @as(*Node, @ptrCast(@alignCast(a)));
 }
 
@@ -1795,7 +1797,7 @@ pub fn elementHasClass(elem: *Element, class: []const u8) !bool {
 }
 
 // elementToNode is an helper to convert an element to a node.
-pub inline fn elementToNode(e: *Element) *Node {
+pub fn elementToNode(e: *Element) *Node {
     return @as(*Node, @ptrCast(@alignCast(e)));
 }
 
@@ -1864,14 +1866,14 @@ fn elementHTMLVtable(elem_html: *ElementHTML) c.dom_html_element_vtable {
 // HTMLScriptElement
 
 // scriptToElt is an helper to convert an script to an element.
-pub inline fn scriptToElt(s: *Script) *Element {
+pub fn scriptToElt(s: *Script) *Element {
     return @as(*Element, @ptrCast(@alignCast(s)));
 }
 
 // HTMLAnchorElement
 
 // anchorToNode is an helper to convert an anchor to a node.
-pub inline fn anchorToNode(a: *Anchor) *Node {
+pub fn anchorToNode(a: *Anchor) *Node {
     return @as(*Node, @ptrCast(@alignCast(a)));
 }
 
@@ -1942,6 +1944,19 @@ pub fn anchorSetRel(a: *Anchor, rel: []const u8) !void {
 
 // HTMLLinkElement
 
+pub fn linkGetRel(link: *Link) ![]const u8 {
+    var res: ?*String = null;
+    const err = c.dom_html_link_element_get_rel(link, &res);
+    try DOMErr(err);
+    if (res == null) return "";
+    return strToData(res.?);
+}
+
+pub fn linkSetRel(link: *Link, rel: []const u8) !void {
+    const err = c.dom_html_link_element_set_rel(link, try strFromData(rel));
+    return DOMErr(err);
+}
+
 pub fn linkGetHref(link: *Link) ![]const u8 {
     var res: ?*String = null;
     const err = c.dom_html_link_element_get_href(link, &res);
@@ -2032,7 +2047,7 @@ pub const OptionCollection = c.dom_html_options_collection;
 // Document Fragment
 pub const DocumentFragment = c.dom_document_fragment;
 
-pub inline fn documentFragmentToNode(doc: *DocumentFragment) *Node {
+pub fn documentFragmentToNode(doc: *DocumentFragment) *Node {
     return @as(*Node, @ptrCast(@alignCast(doc)));
 }
 
@@ -2063,29 +2078,29 @@ fn documentTypeVtable(dt: *DocumentType) c.dom_document_type_vtable {
     return getVtable(c.dom_document_type_vtable, DocumentType, dt);
 }
 
-pub inline fn documentTypeGetName(dt: *DocumentType) ![]const u8 {
+pub fn documentTypeGetName(dt: *DocumentType) ![]const u8 {
     var s: ?*String = null;
     const err = documentTypeVtable(dt).dom_document_type_get_name.?(dt, &s);
     try DOMErr(err);
     return strToData(s.?);
 }
 
-pub inline fn documentTypeGetPublicId(dt: *DocumentType) ![]const u8 {
+pub fn documentTypeGetPublicId(dt: *DocumentType) []const u8 {
     var s: ?*String = null;
     const err = documentTypeVtable(dt).dom_document_type_get_public_id.?(dt, &s);
-    try DOMErr(err);
+    std.debug.assert(err == c.DOM_NO_ERR);
     return strToData(s.?);
 }
 
-pub inline fn documentTypeGetSystemId(dt: *DocumentType) ![]const u8 {
+pub fn documentTypeGetSystemId(dt: *DocumentType) []const u8 {
     var s: ?*String = null;
     const err = documentTypeVtable(dt).dom_document_type_get_system_id.?(dt, &s);
-    try DOMErr(err);
+    std.debug.assert(err == c.DOM_NO_ERR);
     return strToData(s.?);
 }
 
 // DOMImplementation
-pub inline fn domImplementationCreateDocument(
+pub fn domImplementationCreateDocument(
     namespace: ?[:0]const u8,
     qname: ?[:0]const u8,
     doctype: ?*DocumentType,
@@ -2115,7 +2130,7 @@ pub inline fn domImplementationCreateDocument(
     return doc.?;
 }
 
-pub inline fn domImplementationCreateDocumentType(
+pub fn domImplementationCreateDocumentType(
     qname: [:0]const u8,
     publicId: [:0]const u8,
     systemId: [:0]const u8,
@@ -2126,7 +2141,7 @@ pub inline fn domImplementationCreateDocumentType(
     return dt.?;
 }
 
-pub inline fn domImplementationCreateHTMLDocument(title: ?[]const u8) !*DocumentHTML {
+pub fn domImplementationCreateHTMLDocument(title: ?[]const u8) !*DocumentHTML {
     const doc_html = try documentCreateDocument(title);
     const doc = documentHTMLToDocument(doc_html);
 
@@ -2157,18 +2172,18 @@ fn documentVtable(doc: *Document) c.dom_document_vtable {
     return getVtable(c.dom_document_vtable, Document, doc);
 }
 
-pub inline fn documentToNode(doc: *Document) *Node {
+pub fn documentToNode(doc: *Document) *Node {
     return @as(*Node, @ptrCast(@alignCast(doc)));
 }
 
-pub inline fn documentGetElementById(doc: *Document, id: []const u8) !?*Element {
+pub fn documentGetElementById(doc: *Document, id: []const u8) !?*Element {
     var elem: ?*Element = null;
     const err = documentVtable(doc).dom_document_get_element_by_id.?(doc, try strFromData(id), &elem);
     try DOMErr(err);
     return elem;
 }
 
-pub inline fn documentGetElementsByTagName(doc: *Document, tagname: []const u8) !*NodeList {
+pub fn documentGetElementsByTagName(doc: *Document, tagname: []const u8) !*NodeList {
     var nlist: ?*NodeList = null;
     const err = documentVtable(doc).dom_document_get_elements_by_tag_name.?(doc, try strFromData(tagname), &nlist);
     try DOMErr(err);
@@ -2176,7 +2191,7 @@ pub inline fn documentGetElementsByTagName(doc: *Document, tagname: []const u8)
 }
 
 // documentGetDocumentElement returns the root document element.
-pub inline fn documentGetDocumentElement(doc: *Document) !?*Element {
+pub fn documentGetDocumentElement(doc: *Document) !?*Element {
     var elem: ?*Element = null;
     const err = documentVtable(doc).dom_document_get_document_element.?(doc, &elem);
     try DOMErr(err);
@@ -2184,7 +2199,7 @@ pub inline fn documentGetDocumentElement(doc: *Document) !?*Element {
     return elem.?;
 }
 
-pub inline fn documentGetDocumentURI(doc: *Document) ![]const u8 {
+pub fn documentGetDocumentURI(doc: *Document) ![]const u8 {
     var s: ?*String = null;
     const err = documentVtable(doc).dom_document_get_uri.?(doc, &s);
     try DOMErr(err);
@@ -2196,19 +2211,19 @@ pub fn documentSetDocumentURI(doc: *Document, uri: []const u8) !void {
     try DOMErr(err);
 }
 
-pub inline fn documentGetInputEncoding(doc: *Document) ![]const u8 {
+pub fn documentGetInputEncoding(doc: *Document) ![]const u8 {
     var s: ?*String = null;
     const err = documentVtable(doc).dom_document_get_input_encoding.?(doc, &s);
     try DOMErr(err);
     return strToData(s.?);
 }
 
-pub inline fn documentSetInputEncoding(doc: *Document, enc: []const u8) !void {
+pub fn documentSetInputEncoding(doc: *Document, enc: []const u8) !void {
     const err = documentVtable(doc).dom_document_set_input_encoding.?(doc, try strFromData(enc));
     try DOMErr(err);
 }
 
-pub inline fn documentCreateDocument(title: ?[]const u8) !*DocumentHTML {
+pub fn documentCreateDocument(title: ?[]const u8) !*DocumentHTML {
     var doc: ?*Document = null;
     const err = c.dom_implementation_create_document(
         c.DOM_IMPLEMENTATION_HTML,
@@ -2275,42 +2290,42 @@ pub fn documentCreateElementNS(doc: *Document, ns: []const u8, tag_name: []const
     return elem.?;
 }
 
-pub inline fn documentGetDoctype(doc: *Document) !?*DocumentType {
+pub fn documentGetDoctype(doc: *Document) !?*DocumentType {
     var dt: ?*DocumentType = null;
     const err = documentVtable(doc).dom_document_get_doctype.?(doc, &dt);
     try DOMErr(err);
     return dt;
 }
 
-pub inline fn documentCreateDocumentFragment(doc: *Document) !*DocumentFragment {
+pub fn documentCreateDocumentFragment(doc: *Document) !*DocumentFragment {
     var df: ?*DocumentFragment = null;
     const err = documentVtable(doc).dom_document_create_document_fragment.?(doc, &df);
     try DOMErr(err);
     return df.?;
 }
 
-pub inline fn documentCreateTextNode(doc: *Document, s: []const u8) !*Text {
+pub fn documentCreateTextNode(doc: *Document, s: []const u8) !*Text {
     var txt: ?*Text = null;
     const err = documentVtable(doc).dom_document_create_text_node.?(doc, try strFromData(s), &txt);
     try DOMErr(err);
     return txt.?;
 }
 
-pub inline fn documentCreateCDATASection(doc: *Document, s: []const u8) !*CDATASection {
+pub fn documentCreateCDATASection(doc: *Document, s: []const u8) !*CDATASection {
     var cdata: ?*CDATASection = null;
     const err = documentVtable(doc).dom_document_create_cdata_section.?(doc, try strFromData(s), &cdata);
     try DOMErr(err);
     return cdata.?;
 }
 
-pub inline fn documentCreateComment(doc: *Document, s: []const u8) !*Comment {
+pub fn documentCreateComment(doc: *Document, s: []const u8) !*Comment {
     var com: ?*Comment = null;
     const err = documentVtable(doc).dom_document_create_comment.?(doc, try strFromData(s), &com);
     try DOMErr(err);
     return com.?;
 }
 
-pub inline fn documentCreateProcessingInstruction(doc: *Document, target: []const u8, data: []const u8) !*ProcessingInstruction {
+pub fn documentCreateProcessingInstruction(doc: *Document, target: []const u8, data: []const u8) !*ProcessingInstruction {
     var pi: ?*ProcessingInstruction = null;
     const err = documentVtable(doc).dom_document_create_processing_instruction.?(
         doc,
@@ -2322,7 +2337,7 @@ pub inline fn documentCreateProcessingInstruction(doc: *Document, target: []cons
     return pi.?;
 }
 
-pub inline fn documentImportNode(doc: *Document, node: *Node, deep: bool) !*Node {
+pub fn documentImportNode(doc: *Document, node: *Node, deep: bool) !*Node {
     var res: NodeExternal = undefined;
     const nodeext = toNodeExternal(Node, node);
     const err = documentVtable(doc).dom_document_import_node.?(doc, nodeext, deep, &res);
@@ -2330,7 +2345,7 @@ pub inline fn documentImportNode(doc: *Document, node: *Node, deep: bool) !*Node
     return @as(*Node, @ptrCast(@alignCast(res)));
 }
 
-pub inline fn documentAdoptNode(doc: *Document, node: *Node) !*Node {
+pub fn documentAdoptNode(doc: *Document, node: *Node) !*Node {
     var res: NodeExternal = undefined;
     const nodeext = toNodeExternal(Node, node);
     const err = documentVtable(doc).dom_document_adopt_node.?(doc, nodeext, &res);
@@ -2338,14 +2353,14 @@ pub inline fn documentAdoptNode(doc: *Document, node: *Node) !*Node {
     return @as(*Node, @ptrCast(@alignCast(res)));
 }
 
-pub inline fn documentCreateAttribute(doc: *Document, name: []const u8) !*Attribute {
+pub fn documentCreateAttribute(doc: *Document, name: []const u8) !*Attribute {
     var attr: ?*Attribute = null;
     const err = documentVtable(doc).dom_document_create_attribute.?(doc, try strFromData(name), &attr);
     try DOMErr(err);
     return attr.?;
 }
 
-pub inline fn documentCreateAttributeNS(doc: *Document, ns: []const u8, qname: []const u8) !*Attribute {
+pub fn documentCreateAttributeNS(doc: *Document, ns: []const u8, qname: []const u8) !*Attribute {
     var attr: ?*Attribute = null;
     const err = documentVtable(doc).dom_document_create_attribute_ns.?(
         doc,
@@ -2369,7 +2384,7 @@ pub fn documentSetScriptAddedCallback(
 pub const DocumentHTML = c.dom_html_document;
 
 // documentHTMLToNode is an helper to convert a documentHTML to an node.
-pub inline fn documentHTMLToNode(doc: *DocumentHTML) *Node {
+pub fn documentHTMLToNode(doc: *DocumentHTML) *Node {
     return @as(*Node, @ptrCast(@alignCast(doc)));
 }
 
@@ -2486,31 +2501,22 @@ fn parseParams(enc: ?[:0]const u8) c.dom_hubbub_parser_params {
 }
 
 fn parseData(parser: *c.dom_hubbub_parser, reader: anytype) !void {
-    var err: c.hubbub_error = undefined;
-    const TI = @typeInfo(@TypeOf(reader));
-    if (TI == .pointer and @hasDecl(TI.pointer.child, "next")) {
-        while (try reader.next()) |data| {
-            err = c.dom_hubbub_parser_parse_chunk(parser, data.ptr, data.len);
-            try parserErr(err);
-        }
-    } else {
-        var buffer: [1024]u8 = undefined;
-        var ln = buffer.len;
-        while (ln > 0) {
-            ln = try reader.read(&buffer);
-            err = c.dom_hubbub_parser_parse_chunk(parser, &buffer, ln);
-            // TODO handle encoding change error return.
-            // When the HTML contains a META tag with a different encoding than the
-            // original one, a c.DOM_HUBBUB_HUBBUB_ERR_ENCODINGCHANGE error is
-            // returned.
-            // In this case, we must restart the parsing with the new detected
-            // encoding. The detected encoding is stored in the document and we can
-            // get it with documentGetInputEncoding().
-            try parserErr(err);
-        }
+    var buffer: [1024]u8 = undefined;
+    var ln = buffer.len;
+    while (ln > 0) {
+        ln = try reader.read(&buffer);
+        const err = c.dom_hubbub_parser_parse_chunk(parser, &buffer, ln);
+        // TODO handle encoding change error return.
+        // When the HTML contains a META tag with a different encoding than the
+        // original one, a c.DOM_HUBBUB_HUBBUB_ERR_ENCODINGCHANGE error is
+        // returned.
+        // In this case, we must restart the parsing with the new detected
+        // encoding. The detected encoding is stored in the document and we can
+        // get it with documentGetInputEncoding().
+        try parserErr(err);
     }
-    err = c.dom_hubbub_parser_completed(parser);
-    try parserErr(err);
+    const err = c.dom_hubbub_parser_completed(parser);
+    return parserErr(err);
 }
 
 // documentHTMLClose closes the document.
@@ -2519,11 +2525,11 @@ pub fn documentHTMLClose(doc: *DocumentHTML) !void {
     try DOMErr(err);
 }
 
-pub inline fn documentHTMLToDocument(doc_html: *DocumentHTML) *Document {
+pub fn documentHTMLToDocument(doc_html: *DocumentHTML) *Document {
     return @as(*Document, @ptrCast(doc_html));
 }
 
-pub inline fn documentHTMLBody(doc_html: *DocumentHTML) !?*Body {
+pub fn documentHTMLBody(doc_html: *DocumentHTML) !?*Body {
     var body: ?*ElementHTML = null;
     const err = documentHTMLVtable(doc_html).get_body.?(doc_html, &body);
     try DOMErr(err);
@@ -2531,16 +2537,16 @@ pub inline fn documentHTMLBody(doc_html: *DocumentHTML) !?*Body {
     return @as(*Body, @ptrCast(body.?));
 }
 
-pub inline fn bodyToElement(body: *Body) *Element {
+pub fn bodyToElement(body: *Body) *Element {
     return @as(*Element, @ptrCast(@alignCast(body)));
 }
 
-pub inline fn documentHTMLSetBody(doc_html: *DocumentHTML, elt: ?*ElementHTML) !void {
+pub fn documentHTMLSetBody(doc_html: *DocumentHTML, elt: ?*ElementHTML) !void {
     const err = documentHTMLVtable(doc_html).set_body.?(doc_html, elt);
     try DOMErr(err);
 }
 
-pub inline fn documentHTMLGetReferrer(doc: *DocumentHTML) ![]const u8 {
+pub fn documentHTMLGetReferrer(doc: *DocumentHTML) ![]const u8 {
     var s: ?*String = null;
     const err = documentHTMLVtable(doc).get_referrer.?(doc, &s);
     try DOMErr(err);
@@ -2548,7 +2554,7 @@ pub inline fn documentHTMLGetReferrer(doc: *DocumentHTML) ![]const u8 {
     return strToData(s.?);
 }
 
-pub inline fn documentHTMLGetTitle(doc: *DocumentHTML) ![]const u8 {
+pub fn documentHTMLGetTitle(doc: *DocumentHTML) ![]const u8 {
     var s: ?*String = null;
     const err = documentHTMLVtable(doc).get_title.?(doc, &s);
     try DOMErr(err);
@@ -2556,7 +2562,7 @@ pub inline fn documentHTMLGetTitle(doc: *DocumentHTML) ![]const u8 {
     return strToData(s.?);
 }
 
-pub inline fn documentHTMLSetTitle(doc: *DocumentHTML, v: []const u8) !void {
+pub fn documentHTMLSetTitle(doc: *DocumentHTML, v: []const u8) !void {
     const err = documentHTMLVtable(doc).set_title.?(doc, try strFromData(v));
     try DOMErr(err);
 }

src/browser/page.zig

@@ -23,8 +23,8 @@ const Allocator = std.mem.Allocator;
 
 const Dump = @import("dump.zig");
 const State = @import("State.zig");
-const Env = @import("env.zig").Env;
 const Mime = @import("mime.zig").Mime;
+const Browser = @import("browser.zig").Browser;
 const Session = @import("session.zig").Session;
 const Renderer = @import("renderer.zig").Renderer;
 const Window = @import("html/window.zig").Window;
@@ -32,8 +32,10 @@ const Walker = @import("dom/walker.zig").WalkerDepthFirst;
 const Scheduler = @import("Scheduler.zig");
 const Http = @import("../http/Http.zig");
 const ScriptManager = @import("ScriptManager.zig");
+const SlotChangeMonitor = @import("SlotChangeMonitor.zig");
 const HTMLDocument = @import("html/document.zig").HTMLDocument;
 
+const js = @import("js/js.zig");
 const URL = @import("../url.zig").URL;
 
 const log = @import("../log.zig");
@@ -73,7 +75,7 @@ pub const Page = struct {
 
     // Our JavaScript context for this specific page. This is what we use to
     // execute any JavaScript
-    main_context: *Env.JsContext,
+    js: *js.Context,
 
     // indicates intention to navigate to another page on the next loop execution.
     delayed_navigation: bool = false,
@@ -90,6 +92,10 @@ pub const Page = struct {
 
     load_state: LoadState = .parsing,
 
+    // expensive, adds a a global MutationObserver, so we only do it if there's
+    // an "slotchange" event registered
+    slot_change_monitor: ?*SlotChangeMonitor = null,
+
     notified_network_idle: IdleNotification = .init,
     notified_network_almost_idle: IdleNotification = .init,
 
@@ -116,7 +122,7 @@ pub const Page = struct {
         complete,
     };
 
-    pub fn init(self: *Page, arena: Allocator, session: *Session) !void {
+    pub fn init(self: *Page, arena: Allocator, call_arena: Allocator, session: *Session) !void {
         const browser = session.browser;
         const script_manager = ScriptManager.init(browser, self);
 
@@ -126,7 +132,7 @@ pub const Page = struct {
             .window = try Window.create(null, null),
             .arena = arena,
             .session = session,
-            .call_arena = undefined,
+            .call_arena = call_arena,
             .renderer = Renderer.init(arena),
             .state_pool = &browser.state_pool,
             .cookie_jar = &session.cookie_jar,
@@ -135,17 +141,13 @@ pub const Page = struct {
             .scheduler = Scheduler.init(arena),
             .keydown_event_node = .{ .func = keydownCallback },
             .window_clicked_event_node = .{ .func = windowClicked },
-            .main_context = undefined,
+            .js = undefined,
         };
 
-        self.main_context = try session.executor.createJsContext(&self.window, self, self, true, Env.GlobalMissingCallback.init(&self.polyfill_loader));
-        try polyfill.preload(self.arena, self.main_context);
+        self.js = try session.executor.createContext(self, true, js.GlobalMissingCallback.init(&self.polyfill_loader));
+        try polyfill.preload(self.arena, self.js);
 
-        try self.scheduler.add(self, runMicrotasks, 5, .{ .name = "page.microtasks" });
-        // message loop must run only non-test env
-        if (comptime !builtin.is_test) {
-            try self.scheduler.add(self, runMessageLoop, 5, .{ .name = "page.messageLoop" });
-        }
+        try self.registerBackgroundTasks();
     }
 
     pub fn deinit(self: *Page) void {
@@ -155,7 +157,10 @@ pub const Page = struct {
         self.script_manager.deinit();
     }
 
-    fn reset(self: *Page) void {
+    fn reset(self: *Page) !void {
+        // Force running the micro task to drain the queue.
+        self.session.browser.env.runMicrotasks();
+
         self.scheduler.reset();
         self.http_client.abort();
         self.script_manager.reset();
@@ -163,25 +168,38 @@ pub const Page = struct {
         self.load_state = .parsing;
         self.mode = .{ .pre = {} };
         _ = self.session.browser.page_arena.reset(.{ .retain_with_limit = 1 * 1024 * 1024 });
+
+        try self.registerBackgroundTasks();
     }
 
-    fn runMicrotasks(ctx: *anyopaque) ?u32 {
-        const self: *Page = @ptrCast(@alignCast(ctx));
-        self.session.browser.runMicrotasks();
-        return 5;
-    }
+    fn registerBackgroundTasks(self: *Page) !void {
+        if (comptime builtin.is_test) {
+            // HTML test runner manually calls these as necessary
+            return;
+        }
 
-    fn runMessageLoop(ctx: *anyopaque) ?u32 {
-        const self: *Page = @ptrCast(@alignCast(ctx));
-        self.session.browser.runMessageLoop();
-        return 100;
+        try self.scheduler.add(self.session.browser, struct {
+            fn runMicrotasks(ctx: *anyopaque) ?u32 {
+                const b: *Browser = @ptrCast(@alignCast(ctx));
+                b.runMicrotasks();
+                return 5;
+            }
+        }.runMicrotasks, 5, .{ .name = "page.microtasks" });
+
+        try self.scheduler.add(self.session.browser, struct {
+            fn runMessageLoop(ctx: *anyopaque) ?u32 {
+                const b: *Browser = @ptrCast(@alignCast(ctx));
+                b.runMessageLoop();
+                return 100;
+            }
+        }.runMessageLoop, 5, .{ .name = "page.messageLoop" });
     }
 
     pub const DumpOpts = struct {
         // set to include element shadowroots in the dump
         page: ?*const Page = null,
         with_base: bool = false,
-        exclude_scripts: bool = false,
+        strip_mode: Dump.Opts.StripMode = .{},
     };
 
     // dump writes the page content into the given file.
@@ -198,12 +216,12 @@ pub const Page = struct {
                 // returns the <pre> element from the HTML
                 const doc = parser.documentHTMLToDocument(self.window.document);
                 const list = try parser.documentGetElementsByTagName(doc, "pre");
-                const pre = try parser.nodeListItem(list, 0) orelse return error.InvalidHTML;
+                const pre = parser.nodeListItem(list, 0) orelse return error.InvalidHTML;
                 const walker = Walker{};
                 var next: ?*parser.Node = null;
                 while (true) {
                     next = try walker.get_next(pre, next) orelse break;
-                    const v = try parser.nodeTextContent(next.?) orelse return;
+                    const v = parser.nodeTextContent(next.?) orelse return;
                     try out.writeAll(v);
                 }
                 return;
@@ -228,7 +246,7 @@ pub const Page = struct {
 
         try Dump.writeHTML(doc, .{
             .page = opts.page,
-            .exclude_scripts = opts.exclude_scripts,
+            .strip_mode = opts.strip_mode,
         }, out);
     }
 
@@ -241,7 +259,7 @@ pub const Page = struct {
 
         // find <head> tag
         const list = try parser.documentGetElementsByTagName(doc, "head");
-        const head = try parser.nodeListItem(list, 0) orelse return;
+        const head = parser.nodeListItem(list, 0) orelse return;
 
         const base = try parser.documentCreateElement(doc, "base");
         try parser.elementSetAttribute(base, "href", self.url.raw);
@@ -250,11 +268,6 @@ pub const Page = struct {
         try Node.prepend(head, &[_]Node.NodeOrText{.{ .node = parser.elementToNode(base) }});
     }
 
-    pub fn fetchModuleSource(ctx: *anyopaque, src: [:0]const u8) !ScriptManager.BlockingResult {
-        const self: *Page = @ptrCast(@alignCast(ctx));
-        return self.script_manager.blockingGet(src);
-    }
-
     pub fn wait(self: *Page, wait_ms: i32) Session.WaitResult {
         return self._wait(wait_ms) catch |err| {
             switch (err) {
@@ -276,8 +289,8 @@ pub const Page = struct {
         var timer = try std.time.Timer.start();
         var ms_remaining = wait_ms;
 
-        var try_catch: Env.TryCatch = undefined;
-        try_catch.init(self.main_context);
+        var try_catch: js.TryCatch = undefined;
+        try_catch.init(self.js);
         defer try_catch.deinit();
 
         var scheduler = &self.scheduler;
@@ -312,6 +325,12 @@ pub const Page = struct {
                     // mode with an extra socket. Either way, we're waiting
                     // for http traffic
                     if (try http_client.tick(ms_remaining) == .extra_socket) {
+                        // exit_when_done is explicitly set when there isn't
+                        // an extra socket, so it should not be possibl to
+                        // get an extra_socket message when exit_when_done
+                        // is true.
+                        std.debug.assert(exit_when_done == false);
+
                         // data on a socket we aren't handling, return to caller
                         return .extra_socket;
                     }
@@ -347,11 +366,7 @@ pub const Page = struct {
                         std.debug.assert(http_client.intercepted == 0);
 
                         const ms = ms_to_next_task orelse blk: {
-                            // TODO: when jsRunner is fully replaced with the
-                            // htmlRunner, we can remove the first part of this
-                            // condition. jsRunner calls `page.wait` far too
-                            // often to enforce this.
-                            if (wait_ms > 100 and wait_ms - ms_remaining < 100) {
+                            if (wait_ms - ms_remaining < 100) {
                                 // Look, we want to exit ASAP, but we don't want
                                 // to exit so fast that we've run none of the
                                 // background jobs.
@@ -524,7 +539,7 @@ pub const Page = struct {
         if (self.mode != .pre) {
             // it's possible for navigate to be called multiple times on the
             // same page (via CDP). We want to reset the page between each call.
-            self.reset();
+            try self.reset();
         }
 
         log.info(.http, "navigate", .{
@@ -548,7 +563,7 @@ pub const Page = struct {
         const owned_url = try self.arena.dupeZ(u8, request_url);
         self.url = try URL.parse(owned_url, null);
 
-        var headers = try Http.Headers.init();
+        var headers = try self.http_client.newHeaders();
         if (opts.header) |hdr| try headers.add(hdr);
         try self.requestCookie(.{ .is_navigation = true }).headersForRequest(self.arena, owned_url, &headers);
 
@@ -783,7 +798,7 @@ pub const Page = struct {
                         // ignore non-js script.
                         continue;
                     }
-                    try self.script_manager.addFromElement(@ptrCast(node));
+                    try self.script_manager.addFromElement(@ptrCast(node), "page");
                 }
 
                 self.script_manager.staticScriptsDone();
@@ -799,6 +814,9 @@ pub const Page = struct {
                 unreachable;
             },
         }
+
+        // Push the navigation after a successful load.
+        try self.session.history.pushNavigation(self.url.raw, self);
     }
 
     fn pageErrorCallback(ctx: *anyopaque, err: anyerror) void {
@@ -831,7 +849,7 @@ pub const Page = struct {
         _ = self.session.browser.transfer_arena.reset(.{ .retain_with_limit = 4 * 1024 });
     }
 
-    // extracted because this sis called from tests to set things up.
+    // extracted because this is called from tests to set things up.
     pub fn setDocument(self: *Page, html_doc: *parser.DocumentHTML) !void {
         const doc = parser.documentHTMLToDocument(html_doc);
         try parser.documentSetDocumentURI(doc, self.url.raw);
@@ -841,7 +859,7 @@ pub const Page = struct {
         self.window.setStorageShelf(
             try self.session.storage_shed.getOrPut(try self.origin(self.arena)),
         );
-        try self.window.replaceLocation(.{ .url = try self.url.toWebApi(self.arena) });
+        try self.window.changeLocation(self.url.raw, self);
     }
 
     pub const MouseEvent = struct {
@@ -995,6 +1013,31 @@ pub const Page = struct {
         }
     }
 
+    // insertText is a shortcut to insert text into the active element.
+    pub fn insertText(self: *Page, v: []const u8) !void {
+        const Document = @import("dom/document.zig").Document;
+        const element = (try Document.getActiveElement(@ptrCast(self.window.document), self)) orelse return;
+        const node = parser.elementToNode(element);
+
+        const tag = (try parser.nodeHTMLGetTagType(node)) orelse return;
+        switch (tag) {
+            .input => {
+                const input_type = try parser.inputGetType(@ptrCast(element));
+                if (std.mem.eql(u8, input_type, "text")) {
+                    const value = try parser.inputGetValue(@ptrCast(element));
+                    const new_value = try std.mem.concat(self.arena, u8, &.{ value, v });
+                    try parser.inputSetValue(@ptrCast(element), new_value);
+                }
+            },
+            .textarea => {
+                const value = try parser.textareaGetValue(@ptrCast(node));
+                const new_value = try std.mem.concat(self.arena, u8, &.{ value, v });
+                try parser.textareaSetValue(@ptrCast(node), new_value);
+            },
+            else => {},
+        }
+    }
+
     // We cannot navigate immediately as navigating will delete the DOM tree,
     // which holds this event's node.
     // As such we schedule the function to be called as soon as possible.
@@ -1080,9 +1123,9 @@ pub const Page = struct {
         try self.navigateFromWebAPI(action, opts);
     }
 
-    pub fn isNodeAttached(self: *const Page, node: *parser.Node) !bool {
+    pub fn isNodeAttached(self: *const Page, node: *parser.Node) bool {
         const root = parser.documentToNode(parser.documentHTMLToDocument(self.window.document));
-        return root == try parser.nodeGetRootNode(node);
+        return root == parser.nodeGetRootNode(node);
     }
 
     fn elementSubmitForm(self: *Page, element: *parser.Element) !void {
@@ -1111,10 +1154,22 @@ pub const Page = struct {
 
     pub fn stackTrace(self: *Page) !?[]const u8 {
         if (comptime builtin.mode == .Debug) {
-            return self.main_context.stackTrace();
+            return self.js.stackTrace();
         }
         return null;
     }
+
+    pub fn registerSlotChangeMonitor(self: *Page) !void {
+        if (self.slot_change_monitor != null) {
+            return;
+        }
+        self.slot_change_monitor = try SlotChangeMonitor.init(self);
+    }
+
+    pub fn isSameOrigin(self: *const Page, url: []const u8) !bool {
+        const current_origin = try self.origin(self.call_arena);
+        return std.mem.startsWith(u8, url, current_origin);
+    }
 };
 
 pub const NavigateReason = enum {
@@ -1122,6 +1177,7 @@ pub const NavigateReason = enum {
     address_bar,
     form,
     script,
+    history,
 };
 
 pub const NavigateOpts = struct {
@@ -1232,7 +1288,7 @@ pub export fn scriptAddedCallback(ctx: ?*anyopaque, element: ?*parser.Element) c
     // here, else the script_manager will flag it as already-processed.
     _ = parser.elementGetAttribute(element.?, "src") catch return orelse return;
 
-    self.script_manager.addFromElement(element.?) catch |err| {
+    self.script_manager.addFromElement(element.?, "dynamic") catch |err| {
         log.warn(.browser, "dynamic script", .{ .err = err });
     };
 }

src/browser/polyfill/fetch.js

@@ -1,671 +0,0 @@
-// fetch.js code comes from
-// https://github.com/JakeChampion/fetch/blob/main/fetch.js
-//
-// The original code source is available in MIT license.
-//
-// The script comes from the built version from npm.
-// You can get the package with the command:
-//
-// wget $(npm view whatwg-fetch dist.tarball)
-//
-// The source is the content of `package/dist/fetch.umd.js` file.
-(function (global, factory) {
-  typeof exports === 'object' && typeof module !== 'undefined' ? factory(exports) :
-  typeof define === 'function' && define.amd ? define(['exports'], factory) :
-  (factory((global.WHATWGFetch = {})));
-}(this, (function (exports) { 'use strict';
-
-  /* eslint-disable no-prototype-builtins */
-  var g =
-    (typeof globalThis !== 'undefined' && globalThis) ||
-    (typeof self !== 'undefined' && self) ||
-    // eslint-disable-next-line no-undef
-    (typeof global !== 'undefined' && global) ||
-    {};
-
-  var support = {
-    searchParams: 'URLSearchParams' in g,
-    iterable: 'Symbol' in g && 'iterator' in Symbol,
-    blob:
-      'FileReader' in g &&
-      'Blob' in g &&
-      (function() {
-        try {
-          new Blob();
-          return true
-        } catch (e) {
-          return false
-        }
-      })(),
-    formData: 'FormData' in g,
-
-    // Arraybuffer is available but xhr doesn't implement it for now.
-    // arrayBuffer: 'ArrayBuffer' in g
-    arrayBuffer: false
-  };
-
-  function isDataView(obj) {
-    return obj && DataView.prototype.isPrototypeOf(obj)
-  }
-
-  if (support.arrayBuffer) {
-    var viewClasses = [
-      '[object Int8Array]',
-      '[object Uint8Array]',
-      '[object Uint8ClampedArray]',
-      '[object Int16Array]',
-      '[object Uint16Array]',
-      '[object Int32Array]',
-      '[object Uint32Array]',
-      '[object Float32Array]',
-      '[object Float64Array]'
-    ];
-
-    var isArrayBufferView =
-      ArrayBuffer.isView ||
-      function(obj) {
-        return obj && viewClasses.indexOf(Object.prototype.toString.call(obj)) > -1
-      };
-  }
-
-  function normalizeName(name) {
-    if (typeof name !== 'string') {
-      name = String(name);
-    }
-    if (/[^a-z0-9\-#$%&'*+.^_`|~!]/i.test(name) || name === '') {
-      throw new TypeError('Invalid character in header field name: "' + name + '"')
-    }
-    return name.toLowerCase()
-  }
-
-  function normalizeValue(value) {
-    if (typeof value !== 'string') {
-      value = String(value);
-    }
-    return value
-  }
-
-  // Build a destructive iterator for the value list
-  function iteratorFor(items) {
-    var iterator = {
-      next: function() {
-        var value = items.shift();
-        return {done: value === undefined, value: value}
-      }
-    };
-
-    if (support.iterable) {
-      iterator[Symbol.iterator] = function() {
-        return iterator
-      };
-    }
-
-    return iterator
-  }
-
-  function Headers(headers) {
-    this.map = {};
-
-    if (headers instanceof Headers) {
-      headers.forEach(function(value, name) {
-        this.append(name, value);
-      }, this);
-    } else if (Array.isArray(headers)) {
-      headers.forEach(function(header) {
-        if (header.length != 2) {
-          throw new TypeError('Headers constructor: expected name/value pair to be length 2, found' + header.length)
-        }
-        this.append(header[0], header[1]);
-      }, this);
-    } else if (headers) {
-      Object.getOwnPropertyNames(headers).forEach(function(name) {
-        this.append(name, headers[name]);
-      }, this);
-    }
-  }
-
-  Headers.prototype.append = function(name, value) {
-    name = normalizeName(name);
-    value = normalizeValue(value);
-    var oldValue = this.map[name];
-    this.map[name] = oldValue ? oldValue + ', ' + value : value;
-  };
-
-  Headers.prototype['delete'] = function(name) {
-    delete this.map[normalizeName(name)];
-  };
-
-  Headers.prototype.get = function(name) {
-    name = normalizeName(name);
-    return this.has(name) ? this.map[name] : null
-  };
-
-  Headers.prototype.has = function(name) {
-    return this.map.hasOwnProperty(normalizeName(name))
-  };
-
-  Headers.prototype.set = function(name, value) {
-    this.map[normalizeName(name)] = normalizeValue(value);
-  };
-
-  Headers.prototype.forEach = function(callback, thisArg) {
-    for (var name in this.map) {
-      if (this.map.hasOwnProperty(name)) {
-        callback.call(thisArg, this.map[name], name, this);
-      }
-    }
-  };
-
-  Headers.prototype.keys = function() {
-    var items = [];
-    this.forEach(function(value, name) {
-      items.push(name);
-    });
-    return iteratorFor(items)
-  };
-
-  Headers.prototype.values = function() {
-    var items = [];
-    this.forEach(function(value) {
-      items.push(value);
-    });
-    return iteratorFor(items)
-  };
-
-  Headers.prototype.entries = function() {
-    var items = [];
-    this.forEach(function(value, name) {
-      items.push([name, value]);
-    });
-    return iteratorFor(items)
-  };
-
-  if (support.iterable) {
-    Headers.prototype[Symbol.iterator] = Headers.prototype.entries;
-  }
-
-  function consumed(body) {
-    if (body._noBody) return
-    if (body.bodyUsed) {
-      return Promise.reject(new TypeError('Already read'))
-    }
-    body.bodyUsed = true;
-  }
-
-  function fileReaderReady(reader) {
-    return new Promise(function(resolve, reject) {
-      reader.onload = function() {
-        resolve(reader.result);
-      };
-      reader.onerror = function() {
-        reject(reader.error);
-      };
-    })
-  }
-
-  function readBlobAsArrayBuffer(blob) {
-    var reader = new FileReader();
-    var promise = fileReaderReady(reader);
-    reader.readAsArrayBuffer(blob);
-    return promise
-  }
-
-  function readBlobAsText(blob) {
-    var reader = new FileReader();
-    var promise = fileReaderReady(reader);
-    var match = /charset=([A-Za-z0-9_-]+)/.exec(blob.type);
-    var encoding = match ? match[1] : 'utf-8';
-    reader.readAsText(blob, encoding);
-    return promise
-  }
-
-  function readArrayBufferAsText(buf) {
-    var view = new Uint8Array(buf);
-    var chars = new Array(view.length);
-
-    for (var i = 0; i < view.length; i++) {
-      chars[i] = String.fromCharCode(view[i]);
-    }
-    return chars.join('')
-  }
-
-  function bufferClone(buf) {
-    if (buf.slice) {
-      return buf.slice(0)
-    } else {
-      var view = new Uint8Array(buf.byteLength);
-      view.set(new Uint8Array(buf));
-      return view.buffer
-    }
-  }
-
-  function Body() {
-    this.bodyUsed = false;
-
-    this._initBody = function(body) {
-      /*
-        fetch-mock wraps the Response object in an ES6 Proxy to
-        provide useful test harness features such as flush. However, on
-        ES5 browsers without fetch or Proxy support pollyfills must be used;
-        the proxy-pollyfill is unable to proxy an attribute unless it exists
-        on the object before the Proxy is created. This change ensures
-        Response.bodyUsed exists on the instance, while maintaining the
-        semantic of setting Request.bodyUsed in the constructor before
-        _initBody is called.
-      */
-      // eslint-disable-next-line no-self-assign
-      this.bodyUsed = this.bodyUsed;
-      this._bodyInit = body;
-      if (!body) {
-        this._noBody = true;
-        this._bodyText = '';
-      } else if (typeof body === 'string') {
-        this._bodyText = body;
-      } else if (support.blob && Blob.prototype.isPrototypeOf(body)) {
-        this._bodyBlob = body;
-      } else if (support.formData && FormData.prototype.isPrototypeOf(body)) {
-        this._bodyFormData = body;
-      } else if (support.searchParams && URLSearchParams.prototype.isPrototypeOf(body)) {
-        this._bodyText = body.toString();
-      } else if (support.arrayBuffer && support.blob && isDataView(body)) {
-        this._bodyArrayBuffer = bufferClone(body.buffer);
-        // IE 10-11 can't handle a DataView body.
-        this._bodyInit = new Blob([this._bodyArrayBuffer]);
-      } else if (support.arrayBuffer && (ArrayBuffer.prototype.isPrototypeOf(body) || isArrayBufferView(body))) {
-        this._bodyArrayBuffer = bufferClone(body);
-      } else {
-        this._bodyText = body = Object.prototype.toString.call(body);
-      }
-
-      if (!this.headers.get('content-type')) {
-        if (typeof body === 'string') {
-          this.headers.set('content-type', 'text/plain;charset=UTF-8');
-        } else if (this._bodyBlob && this._bodyBlob.type) {
-          this.headers.set('content-type', this._bodyBlob.type);
-        } else if (support.searchParams && URLSearchParams.prototype.isPrototypeOf(body)) {
-          this.headers.set('content-type', 'application/x-www-form-urlencoded;charset=UTF-8');
-        }
-      }
-    };
-
-    if (support.blob) {
-      this.blob = function() {
-        var rejected = consumed(this);
-        if (rejected) {
-          return rejected
-        }
-
-        if (this._bodyBlob) {
-          return Promise.resolve(this._bodyBlob)
-        } else if (this._bodyArrayBuffer) {
-          return Promise.resolve(new Blob([this._bodyArrayBuffer]))
-        } else if (this._bodyFormData) {
-          throw new Error('could not read FormData body as blob')
-        } else {
-          return Promise.resolve(new Blob([this._bodyText]))
-        }
-      };
-    }
-
-    this.arrayBuffer = function() {
-      if (this._bodyArrayBuffer) {
-        var isConsumed = consumed(this);
-        if (isConsumed) {
-          return isConsumed
-        } else if (ArrayBuffer.isView(this._bodyArrayBuffer)) {
-          return Promise.resolve(
-            this._bodyArrayBuffer.buffer.slice(
-              this._bodyArrayBuffer.byteOffset,
-              this._bodyArrayBuffer.byteOffset + this._bodyArrayBuffer.byteLength
-            )
-          )
-        } else {
-          return Promise.resolve(this._bodyArrayBuffer)
-        }
-      } else if (support.blob) {
-        return this.blob().then(readBlobAsArrayBuffer)
-      } else {
-        throw new Error('could not read as ArrayBuffer')
-      }
-    };
-
-    this.text = function() {
-      var rejected = consumed(this);
-      if (rejected) {
-        return rejected
-      }
-
-      if (this._bodyBlob) {
-        return readBlobAsText(this._bodyBlob)
-      } else if (this._bodyArrayBuffer) {
-        return Promise.resolve(readArrayBufferAsText(this._bodyArrayBuffer))
-      } else if (this._bodyFormData) {
-        throw new Error('could not read FormData body as text')
-      } else {
-        return Promise.resolve(this._bodyText)
-      }
-    };
-
-    if (support.formData) {
-      this.formData = function() {
-        return this.text().then(decode)
-      };
-    }
-
-    this.json = function() {
-      return this.text().then(JSON.parse)
-    };
-
-    return this
-  }
-
-  // HTTP methods whose capitalization should be normalized
-  var methods = ['CONNECT', 'DELETE', 'GET', 'HEAD', 'OPTIONS', 'PATCH', 'POST', 'PUT', 'TRACE'];
-
-  function normalizeMethod(method) {
-    var upcased = method.toUpperCase();
-    return methods.indexOf(upcased) > -1 ? upcased : method
-  }
-
-  function Request(input, options) {
-    if (!(this instanceof Request)) {
-      throw new TypeError('Please use the "new" operator, this DOM object constructor cannot be called as a function.')
-    }
-
-    options = options || {};
-    var body = options.body;
-
-    if (input instanceof Request) {
-      if (input.bodyUsed) {
-        throw new TypeError('Already read')
-      }
-      this.url = input.url;
-      this.credentials = input.credentials;
-      if (!options.headers) {
-        this.headers = new Headers(input.headers);
-      }
-      this.method = input.method;
-      this.mode = input.mode;
-      this.signal = input.signal;
-      if (!body && input._bodyInit != null) {
-        body = input._bodyInit;
-        input.bodyUsed = true;
-      }
-    } else {
-      this.url = String(input);
-    }
-
-    this.credentials = options.credentials || this.credentials || 'same-origin';
-    if (options.headers || !this.headers) {
-      this.headers = new Headers(options.headers);
-    }
-    this.method = normalizeMethod(options.method || this.method || 'GET');
-    this.mode = options.mode || this.mode || null;
-    this.signal = options.signal || this.signal || (function () {
-      if ('AbortController' in g) {
-        var ctrl = new AbortController();
-        return ctrl.signal;
-      }
-    }());
-    this.referrer = null;
-
-    if ((this.method === 'GET' || this.method === 'HEAD') && body) {
-      throw new TypeError('Body not allowed for GET or HEAD requests')
-    }
-    this._initBody(body);
-
-    if (this.method === 'GET' || this.method === 'HEAD') {
-      if (options.cache === 'no-store' || options.cache === 'no-cache') {
-        // Search for a '_' parameter in the query string
-        var reParamSearch = /([?&])_=[^&]*/;
-        if (reParamSearch.test(this.url)) {
-          // If it already exists then set the value with the current time
-          this.url = this.url.replace(reParamSearch, '$1_=' + new Date().getTime());
-        } else {
-          // Otherwise add a new '_' parameter to the end with the current time
-          var reQueryString = /\?/;
-          this.url += (reQueryString.test(this.url) ? '&' : '?') + '_=' + new Date().getTime();
-        }
-      }
-    }
-  }
-
-  Request.prototype.clone = function() {
-    return new Request(this, {body: this._bodyInit})
-  };
-
-  function decode(body) {
-    var form = new FormData();
-    body
-      .trim()
-      .split('&')
-      .forEach(function(bytes) {
-        if (bytes) {
-          var split = bytes.split('=');
-          var name = split.shift().replace(/\+/g, ' ');
-          var value = split.join('=').replace(/\+/g, ' ');
-          form.append(decodeURIComponent(name), decodeURIComponent(value));
-        }
-      });
-    return form
-  }
-
-  function parseHeaders(rawHeaders) {
-    var headers = new Headers();
-    // Replace instances of \r\n and \n followed by at least one space or horizontal tab with a space
-    // https://tools.ietf.org/html/rfc7230#section-3.2
-    var preProcessedHeaders = rawHeaders.replace(/\r?\n[\t ]+/g, ' ');
-    // Avoiding split via regex to work around a common IE11 bug with the core-js 3.6.0 regex polyfill
-    // https://github.com/github/fetch/issues/748
-    // https://github.com/zloirock/core-js/issues/751
-    preProcessedHeaders
-      .split('\r')
-      .map(function(header) {
-        return header.indexOf('\n') === 0 ? header.substr(1, header.length) : header
-      })
-      .forEach(function(line) {
-        var parts = line.split(':');
-        var key = parts.shift().trim();
-        if (key) {
-          var value = parts.join(':').trim();
-          try {
-            headers.append(key, value);
-          } catch (error) {
-            console.warn('Response ' + error.message);
-          }
-        }
-      });
-    return headers
-  }
-
-  Body.call(Request.prototype);
-
-  function Response(bodyInit, options) {
-    if (!(this instanceof Response)) {
-      throw new TypeError('Please use the "new" operator, this DOM object constructor cannot be called as a function.')
-    }
-    if (!options) {
-      options = {};
-    }
-
-    this.type = 'default';
-    this.status = options.status === undefined ? 200 : options.status;
-    if (this.status < 200 || this.status > 599) {
-      throw new RangeError("Failed to construct 'Response': The status provided (0) is outside the range [200, 599].")
-    }
-    this.ok = this.status >= 200 && this.status < 300;
-    this.statusText = options.statusText === undefined ? '' : '' + options.statusText;
-    this.headers = new Headers(options.headers);
-    this.url = options.url || '';
-    this._initBody(bodyInit);
-  }
-
-  Body.call(Response.prototype);
-
-  Response.prototype.clone = function() {
-    return new Response(this._bodyInit, {
-      status: this.status,
-      statusText: this.statusText,
-      headers: new Headers(this.headers),
-      url: this.url
-    })
-  };
-
-  Response.error = function() {
-    var response = new Response(null, {status: 200, statusText: ''});
-    response.ok = false;
-    response.status = 0;
-    response.type = 'error';
-    return response
-  };
-
-  var redirectStatuses = [301, 302, 303, 307, 308];
-
-  Response.redirect = function(url, status) {
-    if (redirectStatuses.indexOf(status) === -1) {
-      throw new RangeError('Invalid status code')
-    }
-
-    return new Response(null, {status: status, headers: {location: url}})
-  };
-
-  exports.DOMException = g.DOMException;
-  try {
-    new exports.DOMException();
-  } catch (err) {
-    exports.DOMException = function(message, name) {
-      this.message = message;
-      this.name = name;
-      var error = Error(message);
-      this.stack = error.stack;
-    };
-    exports.DOMException.prototype = Object.create(Error.prototype);
-    exports.DOMException.prototype.constructor = exports.DOMException;
-  }
-
-  function fetch(input, init) {
-    return new Promise(function(resolve, reject) {
-      var request = new Request(input, init);
-
-      if (request.signal && request.signal.aborted) {
-        return reject(new exports.DOMException('Aborted', 'AbortError'))
-      }
-
-      var xhr = new XMLHttpRequest();
-
-      function abortXhr() {
-        xhr.abort();
-      }
-
-      xhr.onload = function() {
-        var options = {
-          statusText: xhr.statusText,
-          headers: parseHeaders(xhr.getAllResponseHeaders() || '')
-        };
-        // This check if specifically for when a user fetches a file locally from the file system
-        // Only if the status is out of a normal range
-        if (request.url.indexOf('file://') === 0 && (xhr.status < 200 || xhr.status > 599)) {
-          options.status = 200;
-        } else {
-          options.status = xhr.status;
-        }
-        options.url = 'responseURL' in xhr ? xhr.responseURL : options.headers.get('X-Request-URL');
-        var body = 'response' in xhr ? xhr.response : xhr.responseText;
-        setTimeout(function() {
-          resolve(new Response(body, options));
-        }, 0);
-      };
-
-      xhr.onerror = function() {
-        setTimeout(function() {
-          reject(new TypeError('Network request failed'));
-        }, 0);
-      };
-
-      xhr.ontimeout = function() {
-        setTimeout(function() {
-          reject(new TypeError('Network request timed out'));
-        }, 0);
-      };
-
-      xhr.onabort = function() {
-        setTimeout(function() {
-          reject(new exports.DOMException('Aborted', 'AbortError'));
-        }, 0);
-      };
-
-      function fixUrl(url) {
-        try {
-          return url === '' && g.location.href ? g.location.href : url
-        } catch (e) {
-          return url
-        }
-      }
-
-      xhr.open(request.method, fixUrl(request.url), true);
-
-      if (request.credentials === 'include') {
-        xhr.withCredentials = true;
-      } else if (request.credentials === 'omit') {
-        xhr.withCredentials = false;
-      }
-
-      if ('responseType' in xhr) {
-        if (support.blob) {
-          xhr.responseType = 'blob';
-        } else if (
-          support.arrayBuffer
-        ) {
-          xhr.responseType = 'arraybuffer';
-        }
-      }
-
-      if (init && typeof init.headers === 'object' && !(init.headers instanceof Headers || (g.Headers && init.headers instanceof g.Headers))) {
-        var names = [];
-        Object.getOwnPropertyNames(init.headers).forEach(function(name) {
-          names.push(normalizeName(name));
-          xhr.setRequestHeader(name, normalizeValue(init.headers[name]));
-        });
-        request.headers.forEach(function(value, name) {
-          if (names.indexOf(name) === -1) {
-            xhr.setRequestHeader(name, value);
-          }
-        });
-      } else {
-        request.headers.forEach(function(value, name) {
-          xhr.setRequestHeader(name, value);
-        });
-      }
-
-      if (request.signal) {
-        request.signal.addEventListener('abort', abortXhr);
-
-        xhr.onreadystatechange = function() {
-          // DONE (success or failure)
-          if (xhr.readyState === 4) {
-            request.signal.removeEventListener('abort', abortXhr);
-          }
-        };
-      }
-
-      xhr.send(typeof request._bodyInit === 'undefined' ? null : request._bodyInit);
-    })
-  }
-
-  fetch.polyfill = true;
-
-  if (!g.fetch) {
-    g.fetch = fetch;
-    g.Headers = Headers;
-    g.Request = Request;
-    g.Response = Response;
-  }
-
-  exports.Headers = Headers;
-  exports.Request = Request;
-  exports.Response = Response;
-  exports.fetch = fetch;
-
-  Object.defineProperty(exports, '__esModule', { value: true });
-
-})));

src/browser/polyfill/fetch.zig

@@ -1,31 +0,0 @@
-// fetch.js code comes from
-// https://github.com/JakeChampion/fetch/blob/main/fetch.js
-//
-// The original code source is available in MIT license.
-//
-// The script comes from the built version from npm.
-// You can get the package with the command:
-//
-// wget $(npm view whatwg-fetch dist.tarball)
-//
-// The source is the content of `package/dist/fetch.umd.js` file.
-pub const source = @embedFile("fetch.js");
-
-const testing = @import("../../testing.zig");
-test "Browser.fetch" {
-    var runner = try testing.jsRunner(testing.tracking_allocator, .{});
-    defer runner.deinit();
-
-    try runner.testCases(&.{
-        .{
-            \\  var ok = false;
-            \\  const request = new Request("http://127.0.0.1:9582/loader");
-            \\  fetch(request).then((response) => { ok = response.ok; });
-            \\  false;
-            ,
-            "false",
-        },
-        // all events have been resolved.
-        .{ "ok", "true" },
-    }, .{});
-}

src/browser/polyfill/polyfill.zig

@@ -19,20 +19,19 @@
 const std = @import("std");
 const builtin = @import("builtin");
 
+const js = @import("../js/js.zig");
 const log = @import("../../log.zig");
 const Allocator = std.mem.Allocator;
-const Env = @import("../env.zig").Env;
 
 pub const Loader = struct {
     state: enum { empty, loading } = .empty,
 
     done: struct {
-        fetch: bool = false,
         webcomponents: bool = false,
     } = .{},
 
-    fn load(self: *Loader, comptime name: []const u8, source: []const u8, js_context: *Env.JsContext) void {
-        var try_catch: Env.TryCatch = undefined;
+    fn load(self: *Loader, comptime name: []const u8, source: []const u8, js_context: *js.Context) void {
+        var try_catch: js.TryCatch = undefined;
         try_catch.init(js_context);
         defer try_catch.deinit();
 
@@ -50,24 +49,12 @@ pub const Loader = struct {
         @field(self.done, name) = true;
     }
 
-    pub fn missing(self: *Loader, name: []const u8, js_context: *Env.JsContext) bool {
+    pub fn missing(self: *Loader, name: []const u8, js_context: *js.Context) bool {
         // Avoid recursive calls during polyfill loading.
         if (self.state == .loading) {
             return false;
         }
 
-        if (!self.done.fetch and isFetch(name)) {
-            const source = @import("fetch.zig").source;
-            self.load("fetch", source, js_context);
-
-            // We return false here: We want v8 to continue the calling chain
-            // to finally find the polyfill we just inserted. If we want to
-            // return false and stops the call chain, we have to use
-            // `info.GetReturnValue.Set()` function, or `undefined` will be
-            // returned immediately.
-            return false;
-        }
-
         if (!self.done.webcomponents and isWebcomponents(name)) {
             const source = @import("webcomponents.zig").source;
             self.load("webcomponents", source, js_context);
@@ -82,6 +69,7 @@ pub const Loader = struct {
         if (comptime builtin.mode == .Debug) {
             log.debug(.unknown_prop, "unkown global property", .{
                 .info = "but the property can exist in pure JS",
+                .stack = js_context.stackTrace() catch "???",
                 .property = name,
             });
         }
@@ -89,22 +77,14 @@ pub const Loader = struct {
         return false;
     }
 
-    fn isFetch(name: []const u8) bool {
-        if (std.mem.eql(u8, name, "fetch")) return true;
-        if (std.mem.eql(u8, name, "Request")) return true;
-        if (std.mem.eql(u8, name, "Response")) return true;
-        if (std.mem.eql(u8, name, "Headers")) return true;
-        return false;
-    }
-
     fn isWebcomponents(name: []const u8) bool {
         if (std.mem.eql(u8, name, "customElements")) return true;
         return false;
     }
 };
 
-pub fn preload(allocator: Allocator, js_context: *Env.JsContext) !void {
-    var try_catch: Env.TryCatch = undefined;
+pub fn preload(allocator: Allocator, js_context: *js.Context) !void {
+    var try_catch: js.TryCatch = undefined;
     try_catch.init(js_context);
     defer try_catch.deinit();
 

src/browser/renderer.zig

@@ -41,6 +41,10 @@ const FlatRenderer = struct {
 
     const Element = @import("dom/element.zig").Element;
 
+    // Define the size of each element in the grid.
+    const default_w = 5;
+    const default_h = 5;
+
     // we expect allocator to be an arena
     pub fn init(allocator: Allocator) FlatRenderer {
         return .{
@@ -62,10 +66,10 @@ const FlatRenderer = struct {
             gop.value_ptr.* = x;
         }
 
-        const _x: f64 = @floatFromInt(x);
+        const _x: f64 = @floatFromInt(x * default_w);
         const y: f64 = 0.0;
-        const w: f64 = 1.0;
-        const h: f64 = 1.0;
+        const w: f64 = default_w;
+        const h: f64 = default_h;
 
         return .{
             .x = _x,
@@ -98,18 +102,20 @@ const FlatRenderer = struct {
     }
 
     pub fn width(self: *const FlatRenderer) u32 {
-        return @max(@as(u32, @intCast(self.elements.items.len)), 1); // At least 1 pixel even if empty
+        return @max(@as(u32, @intCast(self.elements.items.len * default_w)), default_w); // At least default width pixels even if empty
     }
 
     pub fn height(_: *const FlatRenderer) u32 {
-        return 1;
+        return 5;
     }
 
-    pub fn getElementAtPosition(self: *const FlatRenderer, x: i32, y: i32) ?*parser.Element {
-        if (y != 0 or x < 0) {
+    pub fn getElementAtPosition(self: *const FlatRenderer, _x: i32, y: i32) ?*parser.Element {
+        if (y < 0 or y > default_h or _x < 0) {
             return null;
         }
 
+        const x = @divFloor(_x, default_w);
+
         const elements = self.elements.items;
         return if (x < elements.len) @ptrFromInt(elements[@intCast(x)]) else null;
     }