HTML: The Living Standard

Edition for Web Developers — Last Updated 23 July 2021

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:

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.