Re-enable cached property support

The idea is that frequently accessed properties, e.g. window.document, can be
cached directly as data properties on the underlying v8::Object, removing the
need for the access call into Zig. This is only used on a handful of properties,
almost all of which are on the Window. It is important that the property be
read-only. For example, window.location cannot be cached this way because
window.location is writable (e.g. window.location.hash = '#blah').

This existed briefly before Zigdom, but was removed as part of the migration.
The implementation has changed. This previously relied on a "postAttach" feature
which no longer exists. It is not integrated in the bridge/callback directly and
lazily applied after the first access.

src/browser/js/Caller.zig

@@ -82,6 +82,7 @@ pub fn deinit(self: *Caller) void {
 }
 
 pub const CallOpts = struct {
+    cache: ?[]const u8 = null,
     dom_exception: bool = false,
     null_as_undefined: bool = false,
     as_typed_array: bool = false,
@@ -150,9 +151,27 @@ pub fn method(self: *Caller, comptime T: type, func: anytype, handle: *const v8.
 fn _method(self: *Caller, comptime T: type, func: anytype, info: FunctionCallbackInfo, comptime opts: CallOpts) !void {
     const F = @TypeOf(func);
     var args = try self.getArgs(F, 1, info);
-    @field(args, "0") = try TaggedOpaque.fromJS(*T, info.getThis());
+
+    const js_this = info.getThis();
+    @field(args, "0") = try TaggedOpaque.fromJS(*T, js_this);
+
     const res = @call(.auto, func, args);
-    info.getReturnValue().set(try self.local.zigValueToJs(res, opts));
+
+    const mapped = try self.local.zigValueToJs(res, opts);
+    const return_value = info.getReturnValue();
+    return_value.set(mapped);
+
+    if (comptime opts.cache != null) {
+        // store the return value directly in the JS object for faster subsequent
+        // calls. We only do this for a few frequently used properties (e.g. window.document)
+        const local = self.local;
+        const key_handle = local.isolate.initStringHandle(opts.cache.?);
+        var out: v8.MaybeBool = undefined;
+        v8.v8__Object__DefineOwnProperty(js_this, local.handle, key_handle, mapped.handle, 0, &out);
+        if (comptime IS_DEBUG) {
+            std.debug.assert(out.has_value and out.value);
+        }
+    }
 }
 
 pub fn function(self: *Caller, comptime T: type, func: anytype, handle: *const v8.FunctionCallbackInfo, comptime opts: CallOpts) void {

src/browser/js/bridge.zig

@@ -1,4 +1,4 @@
-// Copyright (C) 2023-2025  Lightpanda (Selecy SAS)
+// Copyright (C) 2023-2026  Lightpanda (Selecy SAS)
 //
 // Francis Bouvier <francis@lightpanda.io>
 // Pierre Tachoire <pierre@lightpanda.io>
@@ -164,7 +164,7 @@ pub const Accessor = struct {
 
     const Opts = struct {
         static: bool = false,
-        cache: ?[]const u8 = null, // @ZIGDOM
+        cache: ?[]const u8 = null,
         as_typed_array: bool = false,
         null_as_undefined: bool = false,
     };
@@ -184,11 +184,13 @@ pub const Accessor = struct {
 
                     if (comptime opts.static) {
                         caller.function(T, getter, handle.?, .{
+                            .cache = opts.cache,
                             .as_typed_array = opts.as_typed_array,
                             .null_as_undefined = opts.null_as_undefined,
                         });
                     } else {
                         caller.method(T, getter, handle.?, .{
+                            .cache = opts.cache,
                             .as_typed_array = opts.as_typed_array,
                             .null_as_undefined = opts.null_as_undefined,
                         });

src/browser/webapi/HTMLDocument.zig

@@ -261,7 +261,7 @@ pub const JsApi = struct {
     pub const applets = bridge.accessor(HTMLDocument.getApplets, null, .{});
     pub const plugins = bridge.accessor(HTMLDocument.getEmbeds, null, .{});
     pub const currentScript = bridge.accessor(HTMLDocument.getCurrentScript, null, .{});
-    pub const location = bridge.accessor(HTMLDocument.getLocation, HTMLDocument.setLocation, .{ .cache = "location" });
+    pub const location = bridge.accessor(HTMLDocument.getLocation, HTMLDocument.setLocation, .{});
     pub const all = bridge.accessor(HTMLDocument.getAll, null, .{});
     pub const cookie = bridge.accessor(HTMLDocument.getCookie, HTMLDocument.setCookie, .{});
     pub const doctype = bridge.accessor(HTMLDocument.getDocType, null, .{});

src/browser/webapi/Window.zig

@@ -651,7 +651,7 @@ pub const JsApi = struct {
     pub const localStorage = bridge.accessor(Window.getLocalStorage, null, .{ .cache = "localStorage" });
     pub const sessionStorage = bridge.accessor(Window.getSessionStorage, null, .{ .cache = "sessionStorage" });
     pub const document = bridge.accessor(Window.getDocument, null, .{ .cache = "document" });
-    pub const location = bridge.accessor(Window.getLocation, Window.setLocation, .{ .cache = "location" });
+    pub const location = bridge.accessor(Window.getLocation, Window.setLocation, .{});
     pub const history = bridge.accessor(Window.getHistory, null, .{});
     pub const navigation = bridge.accessor(Window.getNavigation, null, .{});
     pub const crypto = bridge.accessor(Window.getCrypto, null, .{ .cache = "crypto" });