Focus and active element

src/browser/dom/document.zig

@@ -42,6 +42,8 @@ pub const Document = struct {
     pub const prototype = *Node;
     pub const subtype = .node;
 
+    active_element: ?*parser.Element = null,
+
     pub fn constructor(page: *const Page) !*parser.DocumentHTML {
         const doc = try parser.documentCreateDocument(
             try parser.documentHTMLGetTitle(page.window.document),
@@ -242,6 +244,19 @@ 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(doc: *parser.Document, page: *Page) !?ElementUnion {
+        const self = try page.getOrCreateNodeWrapper(Document, @ptrCast(doc));
+        if (self.active_element) |ae| {
+            return try Element.toInterface(ae);
+        }
+
+        if (try parser.documentHTMLBody(page.window.document)) |body| {
+            return try Element.toInterface(@ptrCast(body));
+        }
+
+        return get_documentElement(doc);
+    }
 };
 
 const testing = @import("../../testing.zig");
@@ -412,6 +427,12 @@ 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/dom/element.zig

@@ -368,8 +368,7 @@ 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.
-        const root = try parser.nodeGetRootNode(parser.elementToNode(self));
-        if (root != parser.documentToNode(parser.documentHTMLToDocument(page.window.document))) {
+        if (!try page.isNodeAttached(parser.elementToNode(self))) {
             return DOMRect{ .x = 0, .y = 0, .width = 0, .height = 0 };
         }
         return page.renderer.getRect(self);
@@ -379,8 +378,7 @@ 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 {
-        const root = try parser.nodeGetRootNode(parser.elementToNode(self));
-        if (root != parser.documentToNode(parser.documentHTMLToDocument(page.window.document))) {
+        if (!try page.isNodeAttached(parser.elementToNode(self))) {
             return &.{};
         }
         const heap_ptr = try page.call_arena.create(DOMRect);

src/browser/html/elements.zig

@@ -148,6 +148,27 @@ pub const HTMLElement = struct {
         });
         _ = try parser.elementDispatchEvent(@ptrCast(e), @ptrCast(event));
     }
+
+    const FocusOpts = struct {
+        preventScroll: bool,
+        focusVisible: bool,
+    };
+    pub fn _focus(e: *parser.ElementHTML, _: ?FocusOpts, page: *Page) !void {
+        if (!try page.isNodeAttached(@ptrCast(e))) {
+            return;
+        }
+
+        const root_node = try parser.nodeGetRootNode(@ptrCast(e));
+
+        const Document = @import("../dom/document.zig").Document;
+        const document = try page.getOrCreateNodeWrapper(Document, @ptrCast(root_node));
+
+        // 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.
+        document.active_element = @ptrCast(e);
+    }
 };
 
 // Deprecated HTMLElements in Chrome (2023/03/15)
@@ -1181,4 +1202,11 @@ test "Browser.HTML.Element" {
         .{ "a.href = 'about'", null },
         .{ "a.href", "https://lightpanda.io/opensource-browser/about" },
     }, .{});
+
+    // detached node cannot be focused
+    try runner.testCases(&.{
+        .{ "const focused = document.activeElement", null },
+        .{ "document.createElement('a').focus()", null },
+        .{ "document.activeElement === focused", "true" },
+    }, .{});
 }

src/browser/page.zig

@@ -643,6 +643,11 @@ pub const Page = struct {
         try self.navigateFromWebAPI(action, opts);
     }
 
+    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);
+    }
+
     fn elementSubmitForm(self: *Page, element: *parser.Element) !void {
         const form = (try self.formForElement(element)) orelse return;
         return self.submitForm(@ptrCast(form), @ptrCast(element));