2635-apply-transform-over-each-element-in-array.js

/**
 * @param {number[]} arr
 * @param {Function} fn
 * @return {number[]}
 */
var map = function (arr, fn) {
  for (let i = 0; i < arr.length; ++i) {
    arr[i] = fn(arr[i], i);
  }
  return arr;
};