index.js

// Copyright (c) 2023 by Shakhbozbek Usmonov Miracle Programmer.
// leetcode.com 30 Days of JavaScript challenge

// ----- Started -----

/**
 * @param {Function} fn
 * @param {number} t milliseconds
 * @return {Function}
 */
var debounce = function (fn, t) {
    let timeout;
    return function (...args) {
        clearTimeout(timeout);
        timeout = setTimeout(() => fn.apply(this, args), t);
    };
};

/**
 * const log = debounce(console.log, 100);
 * log('Hello'); // cancelled
 * log('Hello'); // cancelled
 * log('Hello'); // Logged at t=100ms
 */

//----------------------------------------------------------------

/**
 * @param {Array<Function>} functions
 * @return {Promise<any>}
 */
var promiseAll = async function (functions) {
    return new Promise((resolve, reject) => {
        let results = new Array(functions.length);
        let count = 0;
        functions.forEach((fn, i) => {
            fn()
                .then((value) => {
                    results[i] = value;
                    count++;
                    if (count === functions.length) resolve(results);
                })
                .catch((err) => reject(err));
        });
    });
};

/**
 * const promise = promiseAll([() => new Promise(res => res(42))])
 * promise.then(console.log); // [42]
 */

//----------------------------------------------------------------

/**
 * @param {Function} fn
 * @return {Array}
 */
Array.prototype.groupBy = function (fn) {
    return this.reduce((result, item) => {
        const groupKey = fn(item);
        if (!result[groupKey]) {
            result[groupKey] = [];
        }
        result[groupKey].push(item);
        return result;
    }, {});
};

/**
 * [1,2,3].groupBy(String) // {"1":[1],"2":[2],"3":[3]}
 */

//-------------------------------------------------------------

/**
 * @param {Array} arr
 * @param {Function} fn
 * @return {Array}
 */
var sortBy = function (arr, fn) {
    return arr.sort((a, b) => fn(a) - fn(b));
};

//-------------------------------------------------------------

/**
 * @param {Array} arr1
 * @param {Array} arr2
 * @return {Array}
 */
var join = function (arr1, arr2) {
    const result = {};
    for (let i = 0; i < arr1.length; i++) {
        result[arr1[i].id] = arr1[i];
    }
    for (let i = 0; i < arr2.length; i++) {
        if (result[arr2[i].id]) {
            for (const key in arr2[i]) result[arr2[i].id][key] = arr2[i][key];
        } else {
            result[arr2[i].id] = arr2[i];
        }
    }

    return Object.values(result);
};

//-------------------------------------------------------------

/**
 * @param {number[]} nums
 */
var ArrayWrapper = function (nums) {
    this.nums = nums;
};

ArrayWrapper.prototype.valueOf = function () {
    return this.nums.reduce((acc, cur) => acc + cur, 0);
};

ArrayWrapper.prototype.toString = function () {
    return JSON.stringify(this.nums);
};

/**
 * const obj1 = new ArrayWrapper([1,2]);
 * const obj2 = new ArrayWrapper([3,4]);
 * obj1 + obj2; // 10
 * String(obj1); // "[1,2]"
 * String(obj2); // "[3,4]"
 */

//-------------------- END ------------------------