From 14349f058a8a8f3ca47e271aeb3bc53eb0047718 Mon Sep 17 00:00:00 2001
From: Timothy Flynn <trflynn89@pm.me>
Date: Mon, 18 Oct 2021 13:21:23 -0400
Subject: [PATCH] LibWeb: Implement the Element classList attribute

And ensure it is updated (if it exists) when the 'class' attribute is
changed.
---
 Userland/Libraries/LibWeb/DOM/Element.cpp | 10 ++++++++++
 Userland/Libraries/LibWeb/DOM/Element.h   |  3 +++
 Userland/Libraries/LibWeb/DOM/Element.idl |  1 +
 3 files changed, 14 insertions(+)

diff --git a/Userland/Libraries/LibWeb/DOM/Element.cpp b/Userland/Libraries/LibWeb/DOM/Element.cpp
index 58c476de80..b01bbd8f0a 100644
--- a/Userland/Libraries/LibWeb/DOM/Element.cpp
+++ b/Userland/Libraries/LibWeb/DOM/Element.cpp
@@ -12,6 +12,7 @@
 #include <LibWeb/CSS/SelectorEngine.h>
 #include <LibWeb/CSS/StyleInvalidator.h>
 #include <LibWeb/DOM/DOMException.h>
+#include <LibWeb/DOM/DOMTokenList.h>
 #include <LibWeb/DOM/Document.h>
 #include <LibWeb/DOM/Element.h>
 #include <LibWeb/DOM/ExceptionOr.h>
@@ -171,6 +172,8 @@ void Element::parse_attribute(const FlyString& name, const String& value)
         for (auto& new_class : new_classes) {
             m_classes.unchecked_append(new_class);
         }
+        if (m_class_list)
+            m_class_list->associated_attribute_changed(value);
     } else if (name == HTML::AttributeNames::style) {
         auto parsed_style = parse_css_declaration(CSS::ParsingContext(document()), value);
         if (!parsed_style.is_null()) {
@@ -256,6 +259,13 @@ NonnullRefPtr<CSS::StyleProperties> Element::computed_style()
     return properties;
 }
 
+RefPtr<DOMTokenList> const& Element::class_list()
+{
+    if (!m_class_list)
+        m_class_list = DOMTokenList::create(*this, HTML::AttributeNames::class_);
+    return m_class_list;
+}
+
 // https://dom.spec.whatwg.org/#dom-element-matches
 DOM::ExceptionOr<bool> Element::matches(StringView selectors) const
 {
diff --git a/Userland/Libraries/LibWeb/DOM/Element.h b/Userland/Libraries/LibWeb/DOM/Element.h
index 5ae982baa0..7f2d3f4fb1 100644
--- a/Userland/Libraries/LibWeb/DOM/Element.h
+++ b/Userland/Libraries/LibWeb/DOM/Element.h
@@ -58,6 +58,8 @@ public:
     size_t attribute_list_size() const { return m_attributes->length(); }
     NonnullRefPtr<NamedNodeMap> const& attributes() const { return m_attributes; }
 
+    RefPtr<DOMTokenList> const& class_list();
+
     DOM::ExceptionOr<bool> matches(StringView selectors) const;
 
     int client_top() const;
@@ -140,6 +142,7 @@ private:
     RefPtr<CSS::StyleProperties> m_specified_css_values;
     HashMap<String, CSS::StyleComputer::CustomPropertyResolutionTuple> m_custom_properties;
 
+    RefPtr<DOMTokenList> m_class_list;
     Vector<FlyString> m_classes;
 
     RefPtr<ShadowRoot> m_shadow_root;
diff --git a/Userland/Libraries/LibWeb/DOM/Element.idl b/Userland/Libraries/LibWeb/DOM/Element.idl
index aa5ef33882..21a2bfe011 100644
--- a/Userland/Libraries/LibWeb/DOM/Element.idl
+++ b/Userland/Libraries/LibWeb/DOM/Element.idl
@@ -20,6 +20,7 @@ interface Element : Node {
 
     [Reflect] attribute DOMString id;
     [Reflect=class] attribute DOMString className;
+    [SameObject, PutForwards=value] readonly attribute DOMTokenList classList;
 
     boolean matches(DOMString selectors);