1. 9 Communication
    1. 9.1 The MessageEvent interface

9 Communication

9.1 The MessageEvent interface

Messages in server-sent events, Web sockets, cross-document messaging, channel messaging, and broadcast channels use the MessageEvent interface for their message events:

[Constructor(DOMString type, optional MessageEventInit eventInitDict), Exposed=(Window,Worker,AudioWorklet)]
interface MessageEvent : Event {
  readonly attribute any data;
  readonly attribute USVString origin;
  readonly attribute DOMString lastEventId;
  readonly attribute MessageEventSource? source;
  readonly attribute FrozenArray<MessagePort> ports;

  void initMessageEvent(DOMString type, optional boolean bubbles = false, optional boolean cancelable = false, optional any data = null, optional USVString origin = "", optional DOMString lastEventId = "", optional MessageEventSource? source = null, optional sequence<MessagePort> ports = []);
};

dictionary MessageEventInit : EventInit {
  any data = null;
  USVString origin = "";
  DOMString lastEventId = "";
  MessageEventSource? source = null;
  sequence<MessagePort> ports = [];
};

typedef (WindowProxy or MessagePort or ServiceWorker) MessageEventSource;
event . data

Returns the data of the message.

event . origin

Returns the origin of the message, for server-sent events and cross-document messaging.

event . lastEventId

Returns the last event ID string, for server-sent events.

event . source

Returns the WindowProxy of the source window, for cross-document messaging, and the MessagePort being attached, in the connect event fired at SharedWorkerGlobalScope objects.

event . ports

Returns the MessagePort array sent with the message, for cross-document messaging and channel messaging.

Various APIs (e.g., WebSocket, EventSource) use the MessageEvent interface for their message event without using the MessagePort API.