music box solution

music.js

(function() {
    var MusicBox = function() {
        var _albums = [];

        var self = {
            addAlbum: function(album) {
               _albums.push(album);
            },

            favoriteAlbum: function() {
              if ( _albums.length === 0 ) {
                  return null;
              }

              var fav = _albums[0];
              for ( var i=1; i < _albums.length; ++i ) {
                  if ( _albums[i].getPlayCounter() > fav.getPlayCounter() ) {
                      fav = _albums[i];
                  }
              }

              return fav.toString();
            }
        };
        return self;
    };

    var Album = function(artist, title) {
        var _play_counter = 0;
        var self = {
            toString: function() { return artist + " - " + title; },

            play: function() {
               console.log(self.toString());
               _play_counter += 1;
            },

            getPlayCounter: function() { return _play_counter; }
        };

        return self;
    };

    var box = MusicBox(),
        a1  = Album("The Who", "Tommy"),
        a2  = Album("Tom Waits", "Closing Time"),
        a3  = Album("John Cale", "Paris 1919"),
        favorite;

    box.addAlbum(a1);
    box.addAlbum(a2);
    box.addAlbum(a3);

    a1.play(); // prints "Playing The Who - Tommy"
    a2.play(); // prints "Playing John Cale - Paris 1919"
    a1.play(); // prints "Playing The Who - Tommy"

    favorite = box.favoriteAlbum();

    // prints "favorite album is The Who - Tommy"
    console.log("favorite album is " + favorite);

}());