EventSource: message event

The message event of the EventSource API is fired when data is received through an event source.

This event is not cancelable and does not bubble.

Syntax

Use the event name in methods like addEventListener(), or set an event handler property.

addEventListener('message', event => { });

onmessage = event => { };

Event type

Event properties

This interface also inherits properties from its parent, Event.

MessageEvent.data Read only

The data sent by the message emitter.

MessageEvent.origin Read only

A string representing the origin of the message emitter.

MessageEvent.lastEventId Read only

A string representing a unique ID for the event.

MessageEvent.source Read only

A MessageEventSource (which can be a WindowProxy, MessagePort, or ServiceWorker object) representing the message emitter.

MessageEvent.ports Read only

An array of MessagePort objects representing the ports associated with the channel the message is being sent through (where appropriate, e.g. in channel messaging or when sending a message to a shared worker).

Examples

In this basic example, an EventSource is created to receive events from the server; a page with the name sse.php is responsible for generating the events.

var evtSource = new EventSource('sse.php');
var eventList = document.querySelector('ul');

evtSource.addEventListener('message', (e) => {
  var newElement = document.createElement("li");

  newElement.textContent = "message: " + e.data;
  eventList.appendChild(newElement);
});

onmessage equivalent

evtSource.onmessage = (e) => {
  var newElement = document.createElement("li");

  newElement.textContent = "message: " + e.data;
  eventList.appendChild(newElement);
};

Specifications

Specification
HTML Standard
# event-message
HTML Standard
# handler-eventsource-onmessage

Browser compatibility

BCD tables only load in the browser

See also