HTMLTrackElement: cuechange event

The cuechange event fires when a TextTrack has changed the currently displaying cues. The event is fired on both the TextTrack and the HTMLTrackElement in which it's being presented, if any.

You can set up a listener for the cuechange event on a TextTrack using the addEventListener() method:

track.addEventListener('cuechange', function () {
  let cues = track.activeCues;  // array of current cues
});

Or you can just set the oncuechange event handler property:

track.oncuechange = function () {
  let cues = track.activeCues; // array of current cues
}

The underlying TextTrack, indicated by the track property, receives a cuechange event every time the currently-presented cue is changed. This happens even if the track isn't associated with a media element.

If the track is associated with a media element, using the <track> element as a child of the <audio> or <video> element, the cuechange event is also sent to the HTMLTrackElement.

let textTrackElem = document.getElementById("texttrack");

textTrackElem.addEventListener("cuechange", (event) => {
  let cues = event.target.track.activeCues;
});

In addition, you can use the oncuechange event handler:

let textTrackElem = document.getElementById("texttrack");

textTrackElem.oncuechange = (event) => {
  let cues = event.target.track.activeCues;
});

• WebVTT