This is an experimental technology
Check the Browser compatibility table carefully before using this in production.


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

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support Yes ?451 No ? No
ExtendableMessageEvent ? ?451 No ? No
data51 ?451 No ? No
lastEventId ?17451 ? ? No
origin ? ?451 No ? No
ports ? ?451 No ? No
source ? ?451 No ? No
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Basic support No Yes ?45 ? No ?
ExtendableMessageEvent No ? ?45 ? No ?
data No51 ?45 ? No ?
lastEventId No ?1745 ? No ?
origin No ? ?45 ? No ?
ports No ? ?45 ? No ?
source No ? ?45 ? No ?

1. Service workers (and Push) have been disabled in the Firefox 45 & 52 Extended Support Releases (ESR).

See also

Document Tags and Contributors

Contributors to this page: fscholz, chrisdavidmills, jpmedley
Last updated by: fscholz,