RTCDataChannel: message event

{{APIRef("WebRTC")}}

The WebRTC message event is sent to the onmessage event handler on an {{domxref("RTCDataChannel")}} object when a message has been received from the remote peer.

[!NOTE] The message event uses as its event object type the {{domxref("MessageEvent")}} interface defined by the HTML specification.

This event is not cancelable and does not bubble.

Syntax

Use the event name in methods like {{domxref("EventTarget.addEventListener", "addEventListener()")}}, or set an event handler property.

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

onmessage = (event) => { }

Event type

A {{domxref("MessageEvent")}}. Inherits from {{domxref("Event")}}.

{{InheritanceDiagram("MessageEvent")}}

Event properties

Also inherits properties from its parent interface, {{domxref("Event")}}.

• {{domxref("MessageEvent.data")}} {{ReadOnlyInline}}
  • : The data sent by the message emitter.
• {{domxref("MessageEvent.origin")}} {{ReadOnlyInline}}
  • : A string representing the origin of the message emitter.
• {{domxref("MessageEvent.lastEventId")}} {{ReadOnlyInline}}
  • : A string representing a unique ID for the event.
• {{domxref("MessageEvent.source")}} {{ReadOnlyInline}}
  • : A reference to the message emitter, one of {{glossary("WindowProxy")}}, {{domxref("MessagePort")}}, or {{domxref("ServiceWorker")}}.
• {{domxref("MessageEvent.ports")}} {{ReadOnlyInline}}
  • : An array of {{domxref("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).

Examples

For a given {{domxref("RTCDataChannel")}}, dc, created for a peer connection using its {{domxref("RTCPeerConnection.createDataChannel", "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 {{HTMLElement("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 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);
};

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

See also

• WebRTC API
• A simple RTCDataChannel example
• Related events: {{domxref("RTCDataChannel.open_event", "open")}}, {{domxref("RTCDataChannel.close_event", "close")}}, and {{domxref("RTCDataChannel.error_event", "error")}}
• {{domxref("RTCDataChannel.send()")}}