Detached node can't have focus.

Refactor isNodeAttached because of the "law of three."

Author: karlseguin

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

@@ -149,7 +149,11 @@ pub const HTMLElement = struct {
         _ = try parser.elementDispatchEvent(@ptrCast(e), @ptrCast(event));
     }
 
-    pub fn _focus(e: *parser.ElementHTML, page: *Page) void {
+    pub fn _focus(e: *parser.ElementHTML, page: *Page) !void {
+        if (!try page.isNodeAttached(@ptrCast(e))) {
+            return;
+        }
+
         // 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
@@ -1182,4 +1186,11 @@ test "Browser.HTML.Element" {
         .{ "lyric.src = 15", "15" },
         .{ "lyric.src", "15" },
     }, .{});
+
+    // 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

@@ -659,6 +659,11 @@ pub const Page = struct {
         return null;
     }
 
+    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));