platform/video.videojs/dist/video.es.js
function DescriptionsButton(player, options, ready) {
    classCallCheck(this, DescriptionsButton);

    var _this = possibleConstructorReturn(this, _TextTrackButton.call(this, player, options, ready));

    var tracks = player.textTracks();
    var changeHandler = bind(_this, _this.handleTracksChange);

    tracks.addEventListener('change', changeHandler);
    _this.on('dispose', function () {
      tracks.removeEventListener('change', changeHandler);
    });
    return _this;
  }
function DescriptionsButton(player, options, ready) {
    classCallCheck(this, DescriptionsButton);

    var _this = possibleConstructorReturn(this, _TextTrackButton.call(this, player, options, ready));

    var tracks = player.textTracks();
    var changeHandler = bind(_this, _this.handleTracksChange);

    tracks.addEventListener('change', changeHandler);
    _this.on('dispose', function () {
      tracks.removeEventListener('change', changeHandler);
    });
    return _this;
  }
Creates an instance of this class.

@param {Player} player
The `Player` that this class should be attached to.

@param {Object} [options]
The key/value store of player options.

@param {Component~ReadyCallback} [ready]
The function to call when this component is ready.