function setPreviousPlaylist(playlist) {
    /*
      Initializes the previous index
    */
    var previousIndex = null;
    var previousSong = {};

    /*
      If we are repeating the song, then we just start the song over.
    */
    if (_config2.default.repeat_song) {
      /*
        If the playlist is shuffled, get the now playing index.
      */
      if (_config2.default.playlists[playlist].shuffle) {
        previousIndex = _config2.default.playlists[playlist].active_index;
        previousSong = _config2.default.playlists[playlist].shuffle_list[previousIndex];
      } else {
        previousIndex = _config2.default.playlists[playlist].active_index;
        previousSong = _config2.default.playlists[playlist].songs[previousIndex];
      }
    } else {
      /*
        Get the previous index. If the previous index will be less than 0, get the
        last song of the array and continue.
      */
      if (parseInt(_config2.default.playlists[playlist].active_index) - 1 >= 0) {
        previousIndex = parseInt(_config2.default.playlists[playlist].active_index - 1);
      } else {
        previousIndex = parseInt(_config2.default.playlists[playlist].songs.length - 1);
      }

      /*
        If the playlist is shuffled, we grab the song from the shuffle list
      */
      if (_config2.default.playlists[playlist].shuffle) {
        /*
          Grab song from the shuffle list
        */
        previousSong = _config2.default.playlists[playlist].shuffle_list[previousIndex];
      } else {
        /*
          Grab song from the songs array
        */
        previousSong = _config2.default.playlists[playlist].songs[previousIndex];
      }
    }

    /*
      Sets the active playlist to the playlist we are on.
    */
    setActivePlaylist(playlist);

    /*
      Change the song within the playlist.
    */
    changeSongPlaylist(playlist, previousSong, previousIndex);

    /*
      Plays the song
    */
    _core2.default.play();

    /*
      Sync the play pause buttons.
    */
    _playPauseElements2.default.sync();
    _callbacks2.default.run("prev");

    /*
      Repeat the song.
    */
    if (_config2.default.repeat_song) {
      _callbacks2.default.run("song_repeated");
    }
  }
Sets the previous playlist song.

@access private

@prop {string} playlist  - The playlist we are navigating in.