Array.prototype

custom-with-callback.js

const numbersArray = [1, 2, 3, 4];

const logTimesTwo = num => console.log(num * 2);

const customForEach = (arr, cb) => {
  for (let i = 0; i < arr.length; i++) {
    cb(arr[i]);
  }
}

customForEach(numbersArray, logTimesTwo);

custom-without-callback.js

// custom forEach without callback

const numbersArray = [1, 2, 3, 4];

const logTimesTwo = num => console.log(num * 2);

const customForEach = (arr) => {
  for (let i = 0; i < arr.length; i++) {
    logTimesTwo(arr[i]);
  }
}

customForEach(numbersArray);

log-double.js

const numbersArray = [1, 2, 3, 4];

console.log(numbersArray[0]); // 1
console.log(numbersArray[1]); // 2
console.log(numbersArray[2]); // 3
console.log(numbersArray[3]); // 4