TrackEvent
The TrackEvent
interface, which is part of the HTML DOM specification, is used for events which represent changes to a set of available tracks on an HTML media element; these events are addtrack
and removetrack
.
It's important not to confuse TrackEvent
with the RTCTrackEvent
interface, which is used for tracks which are part of an RTCPeerConnection
.
Events based on TrackEvent
are always sent to one of the media track list types:
- Events involving video tracks are always sent to the
VideoTrackList
found inHTMLMediaElement.videoTracks
- Events involving audio tracks are always sent to the
AudioTrackList
specified inHTMLMediaElement.audioTracks
- Events affecting text tracks are sent to the
TextTrackList
object indicated byHTMLMediaElement.textTracks
.
Constructor
TrackEvent()
-
Creates and initializes a new
TrackEvent
object with the event type specified, as well as optional additional properties.
Instance properties
TrackEvent
is based on Event
, so properties of Event
are also available on TrackEvent
objects.
track
Read 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
TrackEvent
has no methods of its own; however, it is based on Event
, so it provides the methods available on Event
objects.
Example
This example sets up a function, handleTrackEvent()
, which is called for any addtrack
or removetrack
event on the first <video>
element found in the document.
js
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 JavaScript instanceof
operator 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