CustomMap.js

// Q. you need to make your own customMap method

// Array.prototype - this is Javascript way of saying 
// "Hey i want to add a brand new method or tool to every single array 
// that ever gets created by atteching the customMap to the prototype
// and any array can now use it"  like [2,3,6,7].customMap(...).   

// thisArg is optional helper. if we want to our callback function to use
// a specific this context inside it. then we pass it
// (Most people don't use this often, but the official JavaScript spec requires it!).

Array.prototype.customMap = function (callback, thisArg) {

    let result = [];

    for (let i = 0; i < this.length; i++) {
        if (i in this) {
            result[i] = callback.call(thisArg, this[i], i, this);
        }
    }

    return result
}

let nums = [2, 4, 6, 8];
let squareArr = nums.customMap((e) => {
    return e ** 2;
})

console.log(squareArr);


// Create a CustomFilter method that works actual like Array.filter() method
Array.prototype.customFilter = function (callback, thisArg) {
    let filtereArr = [];

    for (let i = 0; i < this.length; i++) {

        if (i in this) {
            let passed = callback.call(thisArg, this[i], i, this);
            if (passed) {
                filtereArr.push(this[i])
            }
        }
    }

    return filtereArr;
}

let filteredArr = nums.customFilter((ele) => {
    return ele > 5;
})

console.log(filteredArr);