MessageChannel

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.

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 a message being sent back from the <iframe> (using MessagePort.onmessage), 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

Browser compatibility

Compatibility notes

Channel messaging support for Firefox is close; MessagePort is already being used in shared workers. See bug 952139 for progress.

See also

• Using channel messaging