var _ = {
  map: function(list, cbFn) {
    var newArray = [];
    list.forEach(function(elem, index) {
      var newElem = cbFn(elem, index);
      newArray.push(newElem);
    });
    return newArray;
  }
};

_.map([2, 4, 6], function(num){ return num / 2 ; });

[12, 5, 8, 300, 44].every(x => 4);

var even = _.find([1, 2, 3, 4, 5, 6], function(num){ return num % 2 == 0; });