HTMLTrackElement: cuechange event

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

Bubbles	No
Cancelable	No
Interface	Event
Event handler property	GlobalEventHandlers.oncuechange

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