RTCDataChannel: message event

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since ⁨January 2020⁩.

The WebRTCmessage event is sent to theonmessage event handler on anRTCDataChannel object when a message has been received from the remote peer.

Note:Themessage event uses as its event object type theMessageEvent interface defined by the HTML specification.

This event is not cancelable and does not bubble.

Syntax

Use the event name in methods likeaddEventListener(), or set an event handler property.

addEventListener("message", (event) => { })onmessage = (event) => { }

Event properties

Also inherits properties from its parent interface,Event.

MessageEvent.dataRead only: The data sent by the message emitter.
MessageEvent.originRead only: A string representing the origin of the message emitter.
MessageEvent.lastEventIdRead only: A string representing a unique ID for the event.
MessageEvent.sourceRead only: A reference to the message emitter, one ofWindowProxy,MessagePort, orServiceWorker.
MessageEvent.portsRead only: An array ofMessagePort objects representing the ports associated with the channel the message is being sent through (where appropriate, e.g., in channel messaging or when sending a message to a shared worker).

For a givenRTCDataChannel,dc, created for a peer connection using itscreateDataChannel() method, this code sets up a handler for incoming messages and acts on them by adding the data contained within the message to the current document as a new<p> (paragraph) element.

dc.addEventListener("message", (event) => {  let newParagraph = document.createElement("p");  let textNode = document.createTextNode(event.data);  newParagraph.appendChild(textNode);  document.body.appendChild(newParagraph);});

We first create the new paragraph element and add the message data to it as a new text node. Then we append the new paragraph to the end of the document's body.

You can also use anRTCDataChannel object'sonmessage event handler property to set the event handler:

dc.onmessage = (event) => {  let newParagraph = document.createElement("p");  let textNode = document.createTextNode(event.data);  newParagraph.appendChild(textNode);  document.body.appendChild(newParagraph);};