LibHTML: Add Document::get_element_by_id() and get_elements_by_name()

These will be useful for implementing various things. They don't do any
caching at the moment, but that might become valuable in the future.

To facilitate this change, I also made it possible to abort a tree walk
with for_each_in_subtree() by returning IterationDecision::Break from
the callback.

3 files changed, 31 insertions, 3 deletions

diff --git a/Libraries/LibHTML/DOM/Document.cpp b/Libraries/LibHTML/DOM/Document.cpp
index 4856a71739..c0d1c524a4 100644
--- a/Libraries/LibHTML/DOM/Document.cpp
+++ b/Libraries/LibHTML/DOM/Document.cpp
@@ -193,9 +193,9 @@ void Document::layout()
 void Document::update_style()
 {
     for_each_in_subtree([&](Node& node) {
-        if (!node.needs_style_update())
-            return;
-        to<Element>(node).recompute_style();
+        if (node.needs_style_update())
+            to<Element>(node).recompute_style();
+        return IterationDecision::Continue;
     });
     update_layout();
 }
@@ -242,3 +242,27 @@ void Document::set_hovered_node(Node* node)
 
     invalidate_style();
 }
+
+const Element* Document::get_element_by_id(const String& id) const
+{
+    const Element* element = nullptr;
+    for_each_in_subtree([&](auto& node) {
+        if (is<Element>(node) && to<Element>(node).attribute("id") == id) {
+            element = &to<Element>(node);
+            return IterationDecision::Break;
+        }
+        return IterationDecision::Continue;
+    });
+    return element;
+}
+
+Vector<const Element*> Document::get_elements_by_name(const String& name) const
+{
+    Vector<const Element*> elements;
+    for_each_in_subtree([&](auto& node) {
+        if (is<Element>(node) && to<Element>(node).attribute("name") == name)
+            elements.append(&to<Element>(node));
+        return IterationDecision::Continue;
+    });
+    return elements;
+}
diff --git a/Libraries/LibHTML/DOM/Document.h b/Libraries/LibHTML/DOM/Document.h
index dc3c6c625e..c7c7541748 100644
--- a/Libraries/LibHTML/DOM/Document.h
+++ b/Libraries/LibHTML/DOM/Document.h
@@ -80,6 +80,9 @@ public:
 
     void schedule_style_update();
 
+    const Element* get_element_by_id(const String&) const;
+    Vector<const Element*> get_elements_by_name(const String&) const;
+
 private:
     virtual RefPtr<LayoutNode> create_layout_node(const StyleProperties* parent_style) const override;
 
diff --git a/Libraries/LibHTML/DOM/Node.cpp b/Libraries/LibHTML/DOM/Node.cpp
index 8995a3e689..bebf6b23be 100644
--- a/Libraries/LibHTML/DOM/Node.cpp
+++ b/Libraries/LibHTML/DOM/Node.cpp
@@ -77,6 +77,7 @@ void Node::invalidate_style()
     for_each_in_subtree([&](auto& node) {
         if (is<Element>(node))
             node.set_needs_style_update(true);
+        return IterationDecision::Continue;
     });
     document().schedule_style_update();
 }