JoaoCnh

                          // Let's reduce the array of arrays into a single one
const songNames = allSongs.reduce((acc, currValue) => {
                            return acc.concat(currValue);
                          }, [])
                          // Let's map it out with the seconds turned into minutes 
                          .map(song => {
                            return { ...song, duration: Math.floor(song.duration / 60) };
                          })
                          // Let's filter the ones under 3 minutes
                          .filter(song => {

JoaoCnh

const spotifySongs = [
  { id: 1, name: "Curl of the Burl", artist: "Mastodon", duration: 204 },
  { id: 2, name: "Oblivion", artist: "Mastodon", duration: 306 },
  { id: 3, name: "Flying Whales", artist: "Gojira", duration: 444 },
  { id: 4, name: "L'Enfant Sauvage", artist: "Gojira", duration: 246 }
];

const lastFmSongs = [
  { id: 5, name: "Chop Suey", artist: "System of a Down", duration: 192 },
  { id: 6, name: "Throne", artist: "Bring me the Horizon", duration: 186 },

JoaoCnh

const mult = [songs, [{id: 112, name: "Chop Suey", artist: "System of a Down" }]];

var flatMult = mult.reduce(function (acc, currValue) {
  return acc.concat(currValue);
}, []);

// ES6
const flatMult = mult.reduce((acc, currValue) => {
  return acc.concat(currValue);
}, []);

JoaoCnh

var obj = songs.reduce(function (acc, currValue) {
  var artist = currValue.artist;
  var artistCount = acc[artist] ? acc[artist] + 1 : 1;
  
  var newObj = {};
  newObj[artist] = artistCount;
  
  return Object.assign(acc, newObj);
}, {});

JoaoCnh

const numbers = [2,10,11,5,16];

var sum = numbers.reduce(function (acc, currValue) {
  return acc + currValue;
}, 0);

// ES6
const sum = numbers.reduce((acc, currValue) => {
  return acc + currValue;
}, 0);

JoaoCnh

// using the songs array from previous examples

var mastodonSongs = songs.filter(function (song) {
  return song.artist.toLowerCase() === "mastodon";
});

// ES6
const mastodonSongs = songs.filter(song => {
  return song.artist.toLowerCase() === "mastodon";
});

JoaoCnh

var strings = ["hello", "Matt", "Mastodon", "Cat", "Dog"];

var filtered = strings.filter(function (str) {
  return str.includes("at");
});

// ES6
const filtered = strings.filter(str => {
  return str.includes("at");

JoaoCnh

var numbers = [1,2,3,4,5,6,7,8,9,10];

var evenNumbers = numbers.filter(function (num) {
  return num % 2 === 0;
});

// ES6
const evenNumbers = numbers.filter(num => {
  return num % 2 === 0
});

JoaoCnh

var mapped = songs.map(function (song) {
  // using _.omit we remove the artist property
  // don't use delete because it mutates the song object
  // while _.omit creates a new one
  var newSong = _.omit(song, "artist");
  
  return Object.assign(newSong, {
    scrobbleCount: 0,
    spotifyUrl: "let's just imagine these properties make sense for now",
  });

JoaoCnh

const lowerCaseSongs = songs.map(mySongFunc);

var mySongFunc = function(song) {
  return song.name.toLowerCase();
};

// ES6
const mySongFunc = song => {
  return song.name.toLowerCase();
};