function prev() {
    var playlist = arguments.length > 0 && arguments[0] !== undefined ? arguments[0] : null;

    var prevData = {};

    /*
    If the playlist is empty or null, then we check the active
    playlist
    */
    if (playlist == "" || playlist == null) {
      /*
      If the active playlist is null, then we set the prev global
      song or we set the prev in the playlist.
      */
      if (_config2.default.active_playlist == null || _config2.default.active_playlist == "") {
        _audioNavigation2.default.setPrevious();
      } else {
        _audioNavigation2.default.setPreviousPlaylist(_config2.default.active_playlist);
      }
    } else {
      _audioNavigation2.default.setPreviousPlaylist(playlist);
    }
  }
Plays the prev song either in the playlist or globally.

Public Accessor: Amplitude.prev( playlist );

@access public
@param {string} [playlist = null] 	- The playlist key