The read-only VideoTrackList property length returns the number of entries in the VideoTrackList, each of which is a VideoTrack representing one video track in the media element.

A value of 0 indicates that there are no video tracks in the media.

A number indicating how many video tracks are included in the VideoTrackList. Each track can be accessed by treating the VideoTrackList as an array of objects of type VideoTrack.

This snippet gets the number of video tracks in the first <video> element found in the DOM by querySelector().

const videoElem = document.querySelector("video");
let numVideoTracks = 0;

if (videoElem.videoTracks) {
  numVideoTracks = videoElem.videoTracks.length;
}

Note that this sample checks to be sure HTMLMediaElement.videoTracks is defined, to avoid failing on browsers without support for VideoTrack.