Uses a callback and loop to implement the map functionality of lodash and ruby in Javascript

map.js

"use strict";

var _ = {
  // Implements:
  // https://lodash.com/docs#map
  map: (array, callback) => {
    var newArray = []

    array.forEach(function(item){
      newArray.push(callback(item))
    })

    return newArray
  }
}

// Define a method that multiplies the input by 10
function multiplyBy10(value) {
  return 10 * value;
}
const value = _.map([1, 2, 3], multiplyBy10);

// value => [10, 20, 30]
console.log(value);