daubattu

console.log(users[1]?.girl_friend?.name)
// output: undefined

daubattu

const users = [
  {
    name: 'Nguyễn Hưng Khánh',
    girl_friend: {
      name: 'Nguyễn Thị Khánh',
      address: 'Hà Nội'
    }
  },
  {
    name: 'Nguyễn Văn Khánh'

daubattu

// Written as of ES2019
if (onError) { // Testing if onError really exists
  onError();
}

// Using optional chaining with function calls
onError?.(); // no exception if onError is undefined

daubattu

class User {
  #salary = 1000;
}

const newUser = new User();
console.log(newUser.salary) // undefined

daubattu

const number1 = 10;
const number2 = 0;

// Written as of ES2019
const score1 = number1 || 1;
console.log(score1); // 10
const score2 = number2 || 1;
console.log(score2); // 1

// Using nullish coalescing

daubattu

// Written as of ES2019
await Promise.resolve(console.log('🎉')); // → SyntaxError: await is only valid in async function

(async function() {
  await Promise.resolve(console.log('🎉')); // → 🎉
}());

// Top level await
await Promise.resolve(console.log('🎉')); // → 🎉

daubattu

// Complete the encryption function below.
function encryption(s) {
   const ceil = Math.ceil(Math.sqrt(s.length));
    
   let temp = s;
   let array = [];
      
   while(temp) {
        array = array.concat(temp.substring(0, ceil));
        temp = temp.substring(ceil)

daubattu

//[Hackerrank] Solution of Modified Kaprekar Numbers in JavaScript
function kaprekarNumbers(p, q) {
    let result = [];
    for(let i = p; i <= q; i++) {
        const squareString = (i * i).toString();
        const num1 = squareString.substring(0, squareString.length/2);
        const num2 = squareString.substring(squareString.length/2, squareString.length);
          
        if (Number(num1) + Number(num2) === i) {
            result = result.concat(i)

daubattu

function beautifulTriplets(d, arr) {
    let result = 0;
    for (let i = 0; i < arr.length; i++) {
        const numb1 = arr[i] - d;
        const numb2 = numb1 - d;
        if (arr.includes(numb1) && arr.includes(numb2)) {
            result += 1;
        }
    }
    return result;

daubattu

function minimumDistances(a) {
    let min;
    const findOtherIndex = index => {
    	for (let i = index + 1; i < a.length; i++) {
      	if (a[i] === a[index]) {
        	return i;
        }
      }
      return null;
    }