diff --git a/Userland/Libraries/LibWeb/HTML/MessageEvent.h b/Userland/Libraries/LibWeb/HTML/MessageEvent.h
index 32b80883cb..e08c001eb0 100644
--- a/Userland/Libraries/LibWeb/HTML/MessageEvent.h
+++ b/Userland/Libraries/LibWeb/HTML/MessageEvent.h
@@ -10,13 +10,23 @@
 
 namespace Web::HTML {
 
+struct MessageEventInit : public DOM::EventInit {
+    JS::Value data { JS::js_null() };
+    String origin { "" };
+    String last_event_id { "" };
+};
+
 class MessageEvent : public DOM::Event {
 public:
     using WrapperType = Bindings::MessageEventWrapper;
 
-    static NonnullRefPtr<MessageEvent> create(const FlyString& event_name, JS::Value data, String const& origin)
+    static NonnullRefPtr<MessageEvent> create(FlyString const& event_name, MessageEventInit const& event_init = {})
     {
-        return adopt_ref(*new MessageEvent(event_name, data, origin));
+        return adopt_ref(*new MessageEvent(event_name, event_init));
+    }
+    static NonnullRefPtr<MessageEvent> create_with_global_object(Bindings::WindowObject&, FlyString const& event_name, MessageEventInit const& event_init)
+    {
+        return MessageEvent::create(event_name, event_init);
     }
 
     virtual ~MessageEvent() override = default;
@@ -26,10 +36,11 @@ public:
     String const& last_event_id() const { return m_last_event_id; }
 
 protected:
-    MessageEvent(const FlyString& event_name, JS::Value data, String origin)
-        : DOM::Event(event_name)
-        , m_data(data)
-        , m_origin(move(origin))
+    MessageEvent(FlyString const& event_name, MessageEventInit const& event_init)
+        : DOM::Event(event_name, event_init)
+        , m_data(event_init.data)
+        , m_origin(event_init.origin)
+        , m_last_event_id(event_init.last_event_id)
     {
     }
 
diff --git a/Userland/Libraries/LibWeb/HTML/MessageEvent.idl b/Userland/Libraries/LibWeb/HTML/MessageEvent.idl
index 5eadf05c26..7f5970ddf3 100644
--- a/Userland/Libraries/LibWeb/HTML/MessageEvent.idl
+++ b/Userland/Libraries/LibWeb/HTML/MessageEvent.idl
@@ -1,4 +1,7 @@
+#import <DOM/Event.idl>
+
 interface MessageEvent : Event {
+    constructor(DOMString type, optional MessageEventInit eventInitDict = {});
 
     readonly attribute any data;
     readonly attribute USVString origin;
@@ -6,3 +9,11 @@ interface MessageEvent : Event {
     // FIXME: readonly attribute MessageEventSource? source;
     // FIXME: readonly attribute FrozenArray<MessagePort> ports;
 };
+
+dictionary MessageEventInit : EventInit {
+    any data = null;
+    USVString origin = "";
+    DOMString lastEventId = "";
+    // FIXME: MessageEventSource? source = null;
+    // FIXME: sequence<MessagePort> ports = [];
+};
diff --git a/Userland/Libraries/LibWeb/HTML/MessagePort.cpp b/Userland/Libraries/LibWeb/HTML/MessagePort.cpp
index 9f94ba1f5e..2ae143647e 100644
--- a/Userland/Libraries/LibWeb/HTML/MessagePort.cpp
+++ b/Userland/Libraries/LibWeb/HTML/MessagePort.cpp
@@ -80,7 +80,10 @@ void MessagePort::post_message(JS::Value message)
     // FIXME: This is an ad-hoc hack implementation instead, since we don't currently
     //        have serialization and deserialization of messages.
     main_thread_event_loop().task_queue().add(HTML::Task::create(HTML::Task::Source::PostedMessage, nullptr, [strong_port = NonnullRefPtr { *target_port }, message]() mutable {
-        strong_port->dispatch_event(MessageEvent::create(HTML::EventNames::message, message, "<origin>"));
+        MessageEventInit event_init {};
+        event_init.data = message;
+        event_init.origin = "<origin>";
+        strong_port->dispatch_event(MessageEvent::create(HTML::EventNames::message, event_init));
     }));
 }
 
diff --git a/Userland/Libraries/LibWeb/HTML/WebSocket.cpp b/Userland/Libraries/LibWeb/HTML/WebSocket.cpp
index a73df59177..5094174577 100644
--- a/Userland/Libraries/LibWeb/HTML/WebSocket.cpp
+++ b/Userland/Libraries/LibWeb/HTML/WebSocket.cpp
@@ -203,7 +203,10 @@ void WebSocket::on_message(ByteBuffer message, bool is_text)
         return;
     if (is_text) {
         auto text_message = String(ReadonlyBytes(message));
-        dispatch_event(MessageEvent::create(EventNames::message, JS::js_string(wrapper()->vm(), text_message), url()));
+        MessageEventInit event_init {};
+        event_init.data = JS::js_string(wrapper()->vm(), text_message);
+        event_init.origin = url();
+        dispatch_event(MessageEvent::create(EventNames::message, event_init));
         return;
     }
     // type indicates that the data is Binary and binaryType is "blob"