async.test.js

var async = {
  map: function (arr, iterator, callback) {
    throw "IMPLEMENT ME PLZ"
  },
  mapSeries: function (arr, iterator, callback) {
    throw "IMPLEMENT ME PLZ"
  }
};

var test_arr = [1,2,3,4,5,6,7,8,9,0];

var test_iterator = function (item, callback) {
  setTimeout(function () {
    console.log(item);
    callback(null, item);
  }, Math.random() * 999);
};

var test_callback = function (err, result) {
  console.log(result);
};

async.map(test_arr, test_iterator, test_callback);

// RESULT may be...
// 3
// 1
// ...
// 7 <- random number from 0 to 9
// [1,2,3,4,5,6,7,8,9,0] <- final result

setTimeout(function () {
  async.mapSeries(test_arr, test_iterator, test_callback);

  // RESULT may be...
  // 1
  // 2
  // ...
  // 0 <- in order to test_arr
  // [1,2,3,4,5,6,7,8,9,0] <- final result
}, 1200);