Polyfill
Polyfill for the map function
let arr = [1, 2, 3 ,4, 5];
arr.map((e,i) => e*i);
Array.prototype.myMap = function (cb) {
let res = [];
for(let i=0; i<this.length; i++){
// map(element, index, array)
res.push(cb(this[i], i, this));
}
return res;
}
let newArr = arr.myMap((e,i) => e*i);
console.log(newArr); // [ 0, 2, 6, 12, 20 ]
Polyfill for the filter function
let arr = [1, 2, 3, 4, 5, 6];
Array.prototype.myFilter = function(cb) {
let res = [];
for(let i = 0; i < this.length; i++){
if(cb(this[i], i, this)){
res.push(this[i]);
}
}
return res;
}
let ans = arr.myFilter((el, i, arr) => el <= 4);
console.log(ans); // [1, 2, 3, 4]
Polyfill for the reduce function
let arr = [1, 2, 3, 4, 5];
// let ans = arr.reduce((acc, cur) => {
// return acc + cur
// }, 0)
// Syntax: arr.reduce(function(total, currentValue, currentIndex, arr), initialValue)
Array.prototype.myReduce = function(cb , initialValue) {
let acc = initialValue;
for(let i = 0; i < this.length; i++){
acc = acc ? cb(acc, this[i], i, this) : this[i];
}
return acc;
}
console.log(arr.myReduce((acc, cur) => acc+cur)); // 15
console.log(arr.myReduce((acc, cur) => acc+cur , 2)); // 17
Polyfill for the call function
___ The call() method takes arguments separately. fn.call(obj, "arg1", "arg2", "arg3") ___
const person1 = {name: "Sandeep"};
const person2 = {name: "Abhishek"};
function printSection(section){
console.log(`${this.name} is in class 12-${section}.`);
}
Function.prototype.myCall = function(obj, ...args){
if(typeof this !== 'function'){
throw new Error("Not Callable");
}
obj.fn = this;
obj.fn(args);
}
printSection.myCall(person1, 'C'); // Sandeep is in class 12-C.
printSection.myCall(person2, 'A'); // Abhishek is in class 12-A.
Polyfill for the apply function
___ The apply() method takes arguments as an array. fn.call(obj, ["arg1", "arg2", "arg3"]) ___
const person1 = {name: "Sandeep"};
const person2 = {name: "Abhishek"};
function printStudent(section, background){
console.log(`${this.name} is in class 12-${section}, background = ${background}.`);
}
Function.prototype.myApply = function(obj, args){
if(typeof this !== 'function'){
throw new Error("Not Callable");
}
if (!Array.isArray(args)) {
throw new Error("TypeError: CreateListFromArrayLike called on non-object");
}
obj.fn = this;
obj.fn(...args);
}
printStudent.myApply(person1, ['C', "Science"]); // Sandeep is in class 12-C, background = Science.
printStudent.myApply(person2, ['A', "Arts"]); // Sandeep is in class 12-C, background = Science.
Polyfill for the bind function
const person1 = {name: "Sandeep"};
const person2 = {name: "Abhishek"};
function printStudent(section, background){
console.log(`${this.name} is in class 12-${section}, background = ${background}.`);
}
Function.prototype.myBind = function(obj, ...args){
if(typeof this !== 'function'){
throw new Error("Not Callable");
}
obj.fn = this;
return function(...newArgs){
return obj.fn(...args, ...newArgs);
}
}
const func = printStudent.myBind(person1, 'C');
func("Science"); // Sandeep is in class 12-C, background = Science.
const func2 = printStudent.myBind(person2, 'A', "Arts");
func2(); // Abhishek is in class 12-A, background = Arts.
Polyfill for the Promise
function myPromise(executor){
let onResolve, onReject, isFullfilled = false, isRejected = false, isCalled = false, value;
function resolve(val){
isFullfilled = true;
value = val;
if(typeof onResolve === 'function'){
onResolve(val);
isCalled = true;
};
}
function reject(val){
isRejected = true;
value = val;
if(typeof onResolve === 'function'){
onReject(val);
isCalled = true;
};
}
this.then = function(cb){
onResolve = cb;
if(isFullfilled && !isCalled){
isCalled = true;
onResolve(value)
}
return this;
}
this.catch = function(cb){
onReject = cb;
if(isRejected && !isCalled){
isCalled = true;
onReject(value)
}
return this;
}
try{
executor(resolve, reject)
}catch(error){
reject(error)
}
}
const promise = new myPromise((resolve, reject) => {
resolve(5)
})
promise.then((res) => {
console.log(res);
})
.catch((err) => console.log(err));
Polyfill for the Promise.all()
function func1(){
return new Promise((resolve, reject) => {
resolve("Hello");
})
}
function func2(){
return new Promise((resolve, reject) => {
resolve("World");
})
}
function func3(val){
return new Promise((resolve, reject) => {
resolve(val);
})
}
Promise.promiseAll = (promises) => {
return new Promise((resolve, reject) => {
const result = [];
if(!promises.length){
resolve(result);
return;
}
let pending = promises.length;
promises.forEach((promise, idx) => {
Promise.resolve(promise).then((res) => {
result[idx] = res;
pending--;
if(pending === 0){
resolve(result);
}
}, reject)
})
})
}
Promise.promiseAll([
func1(), func2(), func3("Sandeep")
]).then((res) => console.log(res))
Polyfill for the flat
let arr = [1, 2, [3, [4, 5]]];
// console.log(arr.flat(2)) // [ 1, 2, 3, 4, 5 ]
Array.prototype.myFlat = function(depth){
let res = [];
if(!Array.isArray(this)){
throw new Error(`${this}.myFlat is not a function`);
}
this.forEach((el) => {
if(Array.isArray(el) && depth > 0){
res.push(...el.myFlat(depth-1));
}else{
res.push(el);
}
})
return res;
}
console.log(arr.myFlat(2)); // [ 1, 2, 3, 4, 5 ]
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