Array Multiply Prototype Method

arrayMultiply.js

let integerLists = [1,2,3];

Array.prototype.multiply = function (callback) {
  let list = [];
  for(let i= 0; i < this.length; i++) {
    list.push(callback(this[i], i));
  }
  return list;
};

let multipliedLists = integerLists.multiply(function (item, index) {
  return item * 2;
}); // [2,4,6];

// Without Prototype using map
[1,2,3].map(i => i * 2); // [2,4,6];