MessageChannel: MessageChannel() constructor

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since September 2015.

Note: This feature is available in Web Workers.

The MessageChannel() constructor of the MessageChannel interface returns a new MessageChannel object with two new MessagePort objects.

Syntax

new MessageChannel()

In the following code block, you can see a new channel being created using the MessageChannel() constructor. When the <iframe> has loaded, we pass 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 onmessage), putting it into a paragraph. The port1 is listened to, to check when the message arrives.

js
const channel = new MessageChannel();
const para = document.querySelector("p");

const ifr = document.querySelector("iframe");
const otherWindow = ifr.contentWindow;

ifr.addEventListener("load", iframeLoaded);

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).