JS Array Prototype - Interview Question

array-prototype.js

/**
 * Without calling Array.prototype.map(), Array.prototype.filter(), Array.prototype.reduce(), or
 * Array.prototype.forEach(), implement the following three similar functions on the Array prototype:
 */

/*
 * myMap(callback)
 * Without mutating the original array, this function should call the passed callback function on every
 * element of the array and return a new array containing the result of all these calls, in the corresponding order.
 * The callback function can take up to three parameters:
 * 1. The current value in the array
 * 2. The current index in the array
 * 3. The array itself
 */
Array.prototype.myMap = function (callback) {};

/*
 * myFilter(callback)
 * Without mutating the original array, this function should call the passed callback function on every element
 * of the array and return a new array containing the values of the original array that, when passed to the callback
 * function, returned true. These values should maintain their original order.
 *
 * The callback function takes in the same arguments as the one that the callback function in myMap takes in.
 */
Array.prototype.myFilter = function (callback) {};

/*
 * myReduce(callback, initialValue)
 * Without mutating the original array, this function should call the passed callback function on every element
 * of the array and return the result of the last call to the callback.
 *
 * The callback function can take up to four parameters:
 * 1. The accumulator, which is the return value of the previous call to the callback. On the first call to the
 * callback, the accumulator should be set to the intialValue. If the initialValue is undefined, then it should
 * be set to the first value of the array, and the callback should skip the first element in the array and be
 * called directly on the second element.
 * 2. The current value in the array
 * 3. The current index in the array
 * 4. The array itself
 *
 * If the array contains no elements, the initialValue should be returned. Note that this differs slightly from
 * the Array.prototype.reduce function.
 */
Array.prototype.myReduce = function (callback, initialValue) {};

const arr = [1, 2, 3];
const mappedArray = arr.myMap((value, i, arr) => {
  return value + i + arr[1];
});
const filteredArray = arr.myFilter((value, i, arr) => {
  return value + i + arr[1] > 5;
});
const reducedValue = arr.myReduce((accumulator, value, i, arr) => {
  return accumulator + value + i + arr[1];
}, 3);

console.log(mappedArray); // [3, 5, 7]
console.log(filteredArray); // [3]
console.log(reducedValue); // 18