MessageChannel

Available in workers

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.

Constructor

• MessageChannel()
  • : Returns a new MessageChannel object with two new MessagePort objects.

Instance properties

• port1 Read only
  • : Returns port1 of the channel.
• port2 Read only
  • : Returns port2 of the channel.

Example

In the following example, you can see a new channel being created using the MessageChannel() constructor.

When the IFrame has loaded, we register an onmessage handler for port1 and transfer port2 to the IFrame using the postMessage method along with a message.

When a message is received back from the IFrame, the onMessage function outputs the message to a paragraph.

const channel = new MessageChannel();
const output = document.querySelector(".output");
const iframe = document.querySelector("iframe");

// Wait for the iframe to load
iframe.addEventListener("load", onLoad);

function onLoad() {
  // Listen for messages on port1
  channel.port1.onmessage = onMessage;

  // Transfer port2 to the iframe
  iframe.contentWindow.postMessage("Hello from the main page!", "*", [
    channel.port2,
  ]);
}

// Handle messages received on port1
function onMessage(e) {
  output.innerHTML = e.data;
}

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

Specifications

Browser compatibility

See also

• Using channel messaging