map.js

'use strict';


/**
 * @param {Array} arr
 * @param {Function} cb
 * @returns {Array}
 */
function map(a, b) {
    const result = [];
    a.forEach(x => result.push(b(x)));

    return result;
}

// var array1 = [1, 4, 9, 16];
// console.log(array1.map(x => x * 2));
// console.log(map(array1, x => x * 2));

function reduce(arr, reducer, initial) {
    let i = 0;
    if (initial === undefined) {
        initial = arr[0];
        i = 1;
    }
    while (i < arr.length) {
        initial = reducer(initial, arr[i]);
        i++;
    }

    return initial;
}

const reducer = (a, c) => a + c;
const array2 = [2, 2, 3, 4];
console.log(array2.reduce(reducer));
console.log(reduce(array2, reducer));