VideoTrackList.onchange - Web APIs 编辑

The VideoTrackList property onchange is an event handler which is called when the change event occurs, indicating that a VideoTrack in the VideoTrackList has been made active.

The event is passed into the event handler in the form of an Event object; the event doesn't provide any additional information. To determine the new state of media's tracks, you'll have to look at their VideoTrack.selected flags.

Note: You can also add a handler for the change event using addEventListener().

Syntax

VideoTrackList.onchange = eventHandler;

Value

Set onchange to a function that should be called whenever a track is made active.

Example

This snippet establishes a handler for the change event that looks at each of the tracks in the list, calling a function to update the state of a user interface control that indicates the current state of the track.

var trackList = document.querySelector("video").videoTracks;

trackList.onchange = function(event) {
  trackList.forEach(function(track) {
    updateTrackSelectedButton(track.id, track.selected);
  });
};

The updateTrackSelectedButton(), in this example, should be a function that finds a user interface control using the track's id (perhaps the app uses the track ID as the control element's ID) and the track's selected flag to determine which state the control should be in now.

Specifications

Browser compatibility

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