The port1 read-only property of the MessageChannel interface returns the first port of the message channel, the port attached to the context that originated the channel.

Note: This feature is available in Web Workers.




A MessagePort object, the first port of the channel, that is the port attached to the context that originated the channel.


In the following code block, you can see a new channel being created using the MessageChannel() constructor. When the <iframe> has loaded, we pass MessageChannel.port2 to the <iframe> using MessagePort.postMessage along with a message. The handleMessage handler then responds to a message being sent back from the <iframe> (using MessagePort.onmessage), putting it into a paragraph. The handleMessage method is associated to the port1 to listen when the message arrives.

var channel = new MessageChannel();
var para = document.querySelector('p');
var ifr = document.querySelector('iframe');
var otherWindow = ifr.contentWindow;

ifr.addEventListener("load", iframeLoaded, false);
function iframeLoaded() {
  otherWindow.postMessage('Hello from the main page!', '*', [channel.port2]);

channel.port1.onmessage = handleMessage;
function handleMessage(e) {
  para.innerHTML =;

For a full working example, see our channel messaging basic demo on Github (run it live too).


Specification Status Comment
WHATWG HTML Living Standard
The definition of 'port1' in that specification.
Living Standard No difference from HTML5 Web Messaging.
HTML5 Web Messaging
The definition of 'port1' in that specification.
Recommendation W3C version of the spec

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support 4 41 (41) 10.0 10.6 5
Available in workers (Yes) 41 (41) (Yes) (Yes) (Yes)
Feature Android Chrome for Android Firefox Mobile (Gecko) Firefox OS (Gecko) IE Phone Opera Mobile Safari Mobile
Basic support 4.4 4 41.0 (41) (Yes) 10.0 11.5 5.1
Available in workers (Yes) (Yes) 41.0 (41) (Yes) (Yes) (Yes) (Yes)

See also

Document Tags and Contributors

 Contributors to this page: Sebastianz, chrisdavidmills, teoli, fscholz, kscarfone
 Last updated by: Sebastianz,