docs: function(playlist) {
    this.playlist = playlist;
    this.index = 0;
  
    // Display the title of the first track.
    track.innerHTML = '1. ' + playlist[0].title;
  
    // Setup the playlist display.
    playlist.forEach(function(song) {
      var div = document.createElement('div');
      div.className = 'list-song';
      div.innerHTML = song.title;
      div.onclick = function() {
        player.skipTo(playlist.indexOf(song));
      };
      list.appendChild(div);
    });
  }