const library = function(name, creator) {
  this.name = name;
  this.creator = creator;
  this.tracks = [];
  this.playlists = [];
  this.addTrack = track => this.tracks.push(track);
  this.addPlaylist = playlist => this.playlists.push(playlist);
};

const playlist = function(name) {
  this.name = name;
  this.tracks = [];
  this.addTrack = track => this.tracks.push(track);
  this.plRating = 0;
  this.rating = () => {
    let ratesum = 0;
    for (song in this.tracks) {
      ratesum = ratesum += this.tracks[song].Rating;
    }
    let orating = ratesum / this.tracks.length;
    return orating;
  };
  this.duration = () => {
    let dursum = 0;
    for (song in this.tracks) {
      dursum = dursum += this.tracks[song].length;
    }
    return dursum;
  };
};

const track = function(name, rating, length) {
  this.name = name;
  this.Rating = rating;
  this.length = length;
};

const myLib = new library();
const Dog_Police = new track('Dog Police', 5, 3.1);
const Love_Shack = new track('Love Shack', 10, 3.1);
const Sandstorm = new track('Sandstorm by Darude', 3, 5.3);

const myPL = new playlist('Cool Songs');

myPL.addTrack(Dog_Police);
myPL.addTrack(Love_Shack);
myPL.addTrack(Sandstorm);

console.log(myPL.duration());