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 ports read-only property of the ExtendableMessageEvent interface returns the array containing the MessagePort objects representing the ports of the associated message channel (the channel the message is being sent through.)


var myPorts = ExtendableMessageEventInstance.ports;


An array of MessagePort objects.


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.ports' in that specification.
Working Draft Initial definition.

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support ? 45.0 (45.0)[1] No support ? No support
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 ?

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

See also

Document Tags and Contributors

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