MediaStream: addtrack event

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since ⁨September 2017⁩.

The addtrack event is fired when a new MediaStreamTrack object has been added to a MediaStream.

This event is not cancelable and does not bubble.

Syntax

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

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

onaddtrack = (event) => { }

Also inherits properties from its parent interface, Event.

MediaStreamTrackEvent.track Read only: A MediaStreamTrack object representing the track which was added to the stream.

Using addEventListener():

const stream = new MediaStream();

stream.addEventListener("addtrack", (event) => {
  console.log(`New ${event.track.kind} track added`);
});

Using the onaddtrack event handler property:

const stream = new MediaStream();

stream.onaddtrack = (event) => {
  console.log(`New ${event.track.kind} track added`);
};

Specification
Media Capture and Streams # event-mediastream-addtrack

This page was last modified on ⁨May 2, 2025⁩ by MDN contributors.