JavaScript

async function fetchData() {
  return Promise.resolve('data');
}

async function processData() {
  console.log('start');
  const result = fetchData();
  console.log(typeof result);
  const data = await fetchData();
  console.log(typeof data);
  console.log('end');
}

processData();

class Vehicle {
  #engine = 'V6';
  static count = 0;
  
  constructor(type) {
    this.type = type;
    Vehicle.count++;
  }
  
  static getCount() {
    return this.count;
  }
  
  get info() {
    return `${this.type} with ${this.#engine}`;
  }
}

class Car extends Vehicle {
  static count = 0;
  
  constructor(brand) {
    super('car');
    this.brand = brand;
    Car.count++;
  }
}

const tesla = new Car('Tesla');
const ford = new Car('Ford');
console.log(Vehicle.getCount());
console.log(Car.getCount());
console.log(tesla.info);

function createCounter() {
  let count = 0;
  return function(increment = 1) {
    count += increment;
    return count;
  };
}

const counter1 = createCounter();
const counter2 = createCounter();

console.log(counter1());
console.log(counter1(5));
console.log(counter2(3));
console.log(counter1());
console.log(counter2());

const getValue = (x) => {
  console.log(`Getting: ${x}`);
  return x;
};

const obj = { name: null };

const result = obj.name || getValue('default') && getValue('final');
console.log(`Result: ${result}`);

const numbers = [1, 2, 3, 4, 5];
const result = numbers
  .filter(n => n % 2 === 0)
  .map(n => n * 2)
  .reduce((acc, curr) => acc + curr, 0);

const original = numbers.slice();
numbers.splice(2, 1, 99);

console.log(result);
console.log(numbers);
console.log(original);

const obj = Object.seal({ a: 1, b: { c: 2 } });
obj.a = 10;
obj.b.c = 20;
obj.d = 30;
delete obj.a;

const frozen = Object.freeze({ x: 5, y: { z: 10 } });
frozen.x = 50;
frozen.y.z = 100;
delete frozen.y;

console.log(obj.a, obj.b.c, obj.d, frozen.x, frozen.y.z);