The WebRTC message event is sent to the onmessage event handler on an RTCDataChannel object when a message has been received from the remote peer.

This event is not cancelable and does not bubble.

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

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

onmessage = (event) => {};

A MessageEvent. Inherits from Event.

Also inherits properties from its parent interface, Event.

MessageEvent.data Read only

The data sent by the message emitter.

MessageEvent.origin Read only

A string representing the origin of the message emitter.

MessageEvent.lastEventId Read only

A string representing a unique ID for the event.

MessageEvent.source Read only

A reference to the message emitter, one of WindowProxy, MessagePort, or ServiceWorker.

MessageEvent.ports Read only

An array of MessagePort 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 given RTCDataChannel, dc, created for a peer connection using its createDataChannel() 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);
  },
  false,
);

Lines 2-4 create the new paragraph element and add the message data to it as a new text node. Line 6 appends the new paragraph to the end of the document's body.

You can also use an RTCDataChannel object's onmessage 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);
};

• WebRTC API
• A simple RTCDataChannel example
• Related events: open, close, and error
• RTCDataChannel.send()