TrackEvent
TheTrackEventinterface of theHTML DOM APIis used for events which represent changes to a set of available tracks on an HTML media element; these events areaddtrackandremovetrack.
It's important not to confuseTrackEventwith theRTCTrackEventinterface, which is used for tracks which are part of anRTCPeerConnection.
Events based onTrackEventare always sent to one of the media track list types:
- Events involving video tracks are always sent to the
VideoTrackListfound inHTMLMediaElement.videoTracks - Events involving audio tracks are always sent to the
AudioTrackListspecified inHTMLMediaElement.audioTracks - Events affecting text tracks are sent to the
TextTrackListobject indicated byHTMLMediaElement.textTracks.
Constructor
TrackEvent()-
Creates and initializes a new
TrackEventobject with the event type specified, as well as optional additional properties.
Instance properties
TrackEventis based onEvent,so properties ofEventare also available onTrackEventobjects.
trackRead only-
The DOM track object the event is in reference to. If not
null,this is always an object of one of the media track types:AudioTrack,VideoTrack,orTextTrack).
Instance methods
TrackEventhas no methods of its own; however, it is based onEvent,so it provides the methods available onEventobjects.
Example
This example sets up a function,handleTrackEvent(),which is called for anyaddtrackorremovetrackevent on the first<video>element found in the document.
const videoElem = document.querySelector( "video" );
videoElem.videoTracks.addEventListener( "addtrack", handleTrackEvent, false);
videoElem.videoTracks.addEventListener( "removetrack", handleTrackEvent, false);
videoElem.audioTracks.addEventListener( "addtrack", handleTrackEvent, false);
videoElem.audioTracks.addEventListener( "removetrack", handleTrackEvent, false);
videoElem.textTracks.addEventListener( "addtrack", handleTrackEvent, false);
videoElem.textTracks.addEventListener( "removetrack", handleTrackEvent, false);
function handleTrackEvent(event) {
let trackKind;
if (event.target instanceof VideoTrackList) {
trackKind = "video";
} else if (event.target instanceof AudioTrackList) {
trackKind = "audio";
} else if (event.target instanceof TextTrackList) {
trackKind = "text";
} else {
trackKind = "unknown";
}
switch (event.type) {
case "addtrack":
console.log(`Added a ${trackKind} track`);
break;
case "removetrack":
console.log(`Removed a ${trackKind} track`);
break;
}
}
The event handler uses the JavaScriptinstanceofoperator to determine which type of track the event occurred on, then outputs to console a message indicating what kind of track it is and whether it's being added to or removed from the element.
Specifications
| Specification |
|---|
| HTML Standard #the-trackevent-interface |
Browser compatibility
BCD tables only load in the browser