LibWeb: Implement MediaQueryList.{addListener,removeListener}

Userland/Libraries/LibWeb/CSS/MediaQueryList.cpp

@@ -8,6 +8,7 @@
 #include <LibWeb/CSS/MediaQueryList.h>
 #include <LibWeb/DOM/Document.h>
 #include <LibWeb/DOM/EventDispatcher.h>
+#include <LibWeb/DOM/EventListener.h>
 
 namespace Web::CSS {
 
@@ -46,4 +47,27 @@ JS::Object* MediaQueryList::create_wrapper(JS::GlobalObject& global_object)
     return wrap(global_object, *this);
 }
 
+// https://www.w3.org/TR/cssom-view/#dom-mediaquerylist-addlistener
+void MediaQueryList::add_listener(RefPtr<DOM::EventListener> listener)
+{
+    // 1. If listener is null, terminate these steps.
+    if (!listener)
+        return;
+
+    // 2. Append an event listener to the associated list of event listeners with type set to change,
+    //    callback set to listener, and capture set to false, unless there already is an event listener
+    //    in that list with the same type, callback, and capture.
+    //    (NOTE: capture is set to false by default)
+    add_event_listener(HTML::EventNames::change, listener);
+}
+
+// https://www.w3.org/TR/cssom-view/#dom-mediaquerylist-removelistener
+void MediaQueryList::remove_listener(RefPtr<DOM::EventListener> listener)
+{
+    // 1. Remove an event listener from the associated list of event listeners, whose type is change, callback is listener, and capture is false.
+    // NOTE: While the spec doesn't technically use remove_event_listener and instead manipulates the list directly, every major engine uses remove_event_listener.
+    //       This means if an event listener removes another event listener that comes after it, the removed event listener will not be invoked.
+    remove_event_listener(HTML::EventNames::change, listener);
+}
+
 }