Channel Messaging API

The Channel Messaging API allows two separate scripts running in different browsing contexts attached to the same document (e.g., two IFrames, or the main document and an IFrame, two documents via a SharedWorker, or two workers) to communicate directly, passing messages between one another through two-way channels (or pipes) with a port at each end.

Note: This feature is available in Web Workers

Channel messaging concepts and usage

A message channel is created using the MessageChannel() constructor. Once created, the two ports of the channel can be accessed through the MessageChannel.port1 and MessageChannel.port2 properties (which both return MessagePort objects.) The app that created the channel uses port1, and the app at the other end of the port uses port2 — you send a message to port2, and transfer the port over to the other browsing context using window.postMessage along with two arguments (the message to send, and the object to transfer ownership of, in this case the port itself.)

When these transferable objects are transferred, they are no longer usable on the context they previously belonged to. A port, after it is sent, can no longer be used by the original context.

The other browsing context can listen for the message using MessagePort.onmessage, and grab the contents of the message using the event's data attribute. You could then respond by sending a message back to the original document using MessagePort.postMessage.

When you want to stop sending messages down the channel, you can invoke MessagePort.close to close the ports.

Find out more about how to use this API in Using channel messaging.

Channel messaging interfaces

MessageChannel: Creates a new message channel to send messages across.
MessagePort: Controls the ports on the message channel, allowing sending of messages from one port and listening out for them arriving at the other.
PortCollection: An array of MessagePorts; an experimental solution to allow broadcasting of a message to multiple ports simultaneously.

Examples

We have published a channel messaging basic demo on Github (run it live too), which shows a really simple single message transfer between a page and an embedded <iframe>.
You can also see a multimessaging demo (run this live), which shows a slightly more complex setup that can send multiple messages between main page and IFrame.

Specifications

Specification
HTML Standard (HTML) # message-channels

Browser compatibility

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	WebView Android	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet
`Channel_Messaging_API`	4	12	41	10	10.6	5	≤37	18	41	11	4.2	1.0
`close`	4	12	41	10	10.6	5	≤37	18	41	11	4.2	1.0
`message_event`	4	12	Yes	10	10.6	5	≤37	18	No	11.5	4.2	1.0
`messageerror_event`	60	18	57	No	47	No See bug 171216.	60	60	57	47	No See bug 171216.	8.0
`onmessage`	4	12	41	10	10.6	5	≤37	18	41	11	4.2	1.0
`onmessageerror`	60	18	57	No	47	No See bug 171216.	60	60	57	44	No See bug 171216.	8.0
`postMessage`	4	12	41	10	10.6	5	≤37	18	41	11	4.2	1.0
`start`	4	12	41	10	10.6	5	≤37	18	41	11	4.2	1.0
`worker_support`	4	12	41	10	≤15	5	≤37	18	41	≤14	5	1.0

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	WebView Android	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet
`Channel_Messaging_API`	4	12	41	10	10.6	5	4.4	18	41	11	4.2	1.0
`MessageChannel`	4	12	41	10	10.6	5	4.4	18	41	11	4.2	1.0
`port1`	4	12	41	10	10.6	5	4.4	18	41	11	4.2	1.0
`port2`	4	12	41	10	10.6	5	4.4	18	41	11	4.2	1.0

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MessagePort