MessageChannel
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 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
MessageChannelobject with two newMessagePortobjects.
Instance properties
MessageChannel.port1Read onlyReturns port1 of the channel.
MessageChannel.port2Read onlyReturns 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 MessageChannel.port1 and transfer MessageChannel.port2 to the IFrame using the window.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
| Specification |
|---|
| HTML # message-channels |
