Add document.activeElement and HTMLElement.focus()

src/browser/dom/document.zig

@@ -242,6 +242,11 @@ pub const Document = struct {
     pub fn _createTreeWalker(_: *parser.Document, root: *parser.Node, what_to_show: ?u32, filter: ?TreeWalker.TreeWalkerOpts) !TreeWalker {
         return try TreeWalker.init(root, what_to_show, filter);
     }
+
+    pub fn get_activeElement(_: *parser.Document, page: *const Page) !?ElementUnion {
+        const el = (try page.activeElement()) orelse return null;
+        return try Element.toInterface(el);
+    }
 };
 
 const testing = @import("../../testing.zig");
@@ -412,6 +417,12 @@ test "Browser.DOM.Document" {
         },
     }, .{});
 
+    try runner.testCases(&.{
+        .{ "document.activeElement === document.body", "true" },
+        .{ "document.getElementById('link').focus()", "undefined" },
+        .{ "document.activeElement === document.getElementById('link')", "true" },
+    }, .{});
+
     // this test breaks the doc structure, keep it at the end of the test
     // suite.
     try runner.testCases(&.{

src/browser/html/elements.zig

@@ -148,6 +148,14 @@ pub const HTMLElement = struct {
         });
         _ = try parser.elementDispatchEvent(@ptrCast(e), @ptrCast(event));
     }
+
+    pub fn _focus(e: *parser.ElementHTML, page: *Page) void {
+        // TODO: some elements can't be focused, like if they're disabled
+        // but there doesn't seem to be a generic way to check this. For example
+        // we could look for the "disabled" attribute, but that's only meaningful
+        // on certain types, and libdom's vtable doesn't seem to expose this.
+        page.active_element = @ptrCast(e);
+    }
 };
 
 // Deprecated HTMLElements in Chrome (2023/03/15)

src/browser/page.zig

@@ -95,6 +95,8 @@ pub const Page = struct {
     // indicates intention to navigate to another page on the next loop execution.
     delayed_navigation: bool = false,
 
+    active_element: ?*parser.Element = null,
+
     pub fn init(self: *Page, arena: Allocator, session: *Session) !void {
         const browser = session.browser;
         self.* = .{
@@ -643,6 +645,23 @@ pub const Page = struct {
         try self.navigateFromWebAPI(action, opts);
     }
 
+    pub fn activeElement(self: *const Page) !?*parser.Element {
+        if (self.active_element) |ae| {
+            return ae;
+        }
+
+        if (try parser.documentHTMLBody(self.window.document)) |body| {
+            return @ptrCast(body);
+        }
+
+        const doc = self.window.document;
+        if (try parser.documentGetDocumentElement(@ptrCast(doc))) |de| {
+            return @ptrCast(de);
+        }
+
+        return null;
+    }
+
     fn elementSubmitForm(self: *Page, element: *parser.Element) !void {
         const form = (try self.formForElement(element)) orelse return;
         return self.submitForm(@ptrCast(form), @ptrCast(element));