30 Days of Javascript 5 - Apply Transform Over Each Element in Array

Given an integer array arr and a mapping function fn, return a new array with a transformation applied to each element.

The returned array should be created such that returnedArray[i] = fn(arr[i], i).

Please solve it without the built-in Array.map method.

Example 1:

Input: arr = [1,2,3], fn = function plusone(n) { return n + 1; } Output: [2,3,4] Explanation: const newArray = map(arr, plusone); // [2,3,4] The function increases each value in the array by one. Example 2:

Input: arr = [1,2,3], fn = function plusI(n, i) { return n + i; } Output: [1,3,5] Explanation: The function increases each value by the index it resides in. Example 3:

Input: arr = [10,20,30], fn = function constant() { return 42; } Output: [42,42,42] Explanation: The function always returns 42.

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

Inside the map function, a new array called returnedArray is declared to store the results of applying the callback function to each element of the original array. A for loop is used to iterate over each element of the arr array. Within each iteration of the loop, the callback function fn is called with two arguments: the current element of the arr array (arr[i]) and the index of that element (i). The result of the callback function is assigned to the corresponding index of the returnedArray. After iterating over all elements of the arr array, the returnedArray is returned as the result of the map function.