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 'neutered' on the previous context — the one they previously belonged to. For instance a port, when is sent, cannot be used anymore by the original context. Note that the only two objects that can currently be transferred are ArrayBuffer and MessagePort.

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

Specifications

Specification Status Comment
HTML Living Standard
The definition of 'Channel messaging' in that specification.
Living Standard  

Browser compatibility

MessageChannel

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
Basic supportChrome Full support 4Edge Full support YesFirefox Full support 41IE Full support 10Opera Full support 10.6Safari Full support 5WebView Android Full support 4.4Chrome Android Full support 18Edge Mobile Full support YesFirefox Android Full support 41Opera Android Full support 11.5Safari iOS Full support 5.1Samsung Internet Android ?

Legend

Full support  
Full support
Compatibility unknown  
Compatibility unknown

MessagePort

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
Basic supportChrome Full support 4Edge Full support YesFirefox Full support YesIE Full support 10Opera Full support 10.6Safari Full support 5WebView Android Full support YesChrome Android Full support 18Edge Mobile Full support YesFirefox Android Full support YesOpera Android Full support 11.5Safari iOS Full support 5.1Samsung Internet Android ?

Legend

Full support  
Full support
Compatibility unknown  
Compatibility unknown

See also

Document Tags and Contributors

Last updated by: fscholz,