TextTrack.id

The id read-only property of the TextTrack interface returns the ID of the track if it has one.

A string containing the ID, or an empty string.

In the following example the value of id is printed to the console.

let video = document.querySelector('video');
  let track = video.addTextTrack("captions", "Captions", "en");
  track.mode = "showing";
  console.log(track.id);