This is an experimental technology
Because this technology's specification has not stabilized, check the compatibility table for usage in various browsers. Also note that the syntax and behavior of an experimental technology is subject to change in future versions of browsers as the specification changes.


The ExtendableMessageEvent interface of the ServiceWorker API represents the event object of a message event fired on a service worker (when a channel message is received on the ServiceWorkerGlobalScope from another context) — extends the lifetime of such events.

This interface inherits from the ExtendableEvent interface.


Creates a new ExtendableMessageEvent object instance.


Inherits properties from its parent, ExtendableEvent.

ExtendableMessageEvent.data Read only
Returns the event's data. It can be any data type.
ExtendableMessageEvent.origin Read only
Returns the origin of the ServiceWorkerClient that sent the message
ExtendableMessageEvent.lastEventId Read only
Represents, in server-sent events, the last event ID of the event source.
ExtendableMessageEvent.source Read only
Returns a reference to the service worker that sent the message.
ExtendableMessageEvent.ports Read only
Returns the array containing the MessagePort objects representing the ports of the associated message channel.


Inherits methods from its parent, ExtendableEvent.


When the following code is used inside a service worker to respond to a push messages by sending the data received via PushMessageData to the main context via a channel message, the event object of onmessage will be a ExtendableMessageEvent.

var port;

self.addEventListener('push', function(e) {
  var obj = e.data.json();

  if(obj.action === 'subscribe' || obj.action === 'unsubscribe') {
  } else if(obj.action === 'init' || obj.action === 'chatMsg') {

self.onmessage = function(e) {
  port = e.ports[0];


Specification Status Comment
Service Workers
The definition of 'ExtendableMessageEvent' in that specification.
Working Draft Initial definition.

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support (Yes) 45.0 (45.0)[1] No support ? No support
data property 51.0 ? ? ? ?
Feature Android Android Webview Firefox Mobile (Gecko) Firefox OS IE Mobile Opera Mobile Safari Mobile Chrome for Android
Basic support No support No support (Yes) (Yes) No support ? No support (Yes)
data property No support No support ? ? ? ? ? 51.0

[1] Service workers (and Push) have been disabled in the Firefox 45 Extended Support Release (ESR.)

See also


© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.

API Experimental ExtendableMessageEvent Interface Reference Service Workers