The MessageChannel interface of the Channel Messaging API allows us to create a new message channel and send data through it via its two MessagePort properties.

Note: This feature is available in Web Workers.

Properties

MessageChannel.port1 Read only
Returns port1 of the channel.
MessageChannel.port2 Read only
Returns port2 of the channel.

Constructor

MessageChannel()

Returns a new MessageChannel object with two new MessagePort objects.

Example

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 the message being sent back from the <iframe> (using MessagePort.onmessage), by putting it into a paragraph.

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 = e.data;
}   

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

Specifications

Specification Status Comment
WHATWG HTML Living Standard
The definition of 'MessageChannel' in that specification.
Living Standard No difference from HTML5 Web Messaging.

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

 Last updated by: jsx,