JavaScript

console.log(typeof myVar);
console.log(typeof myFunc);
console.log(typeof myArrow);

var myVar = 'initialized';

function myFunc() {
  return 'function declaration';
}

var myArrow = () => 'arrow function';

console.log(typeof myVar);
console.log(typeof myFunc);
console.log(typeof myArrow);

const config = { api: 'v1', timeout: 5000 };
Object.seal(config);

const settings = { theme: 'dark', lang: 'en' };
Object.freeze(settings);

config.api = 'v2';
config.retries = 3;
settings.theme = 'light';
settings.debug = true;

console.log(config.api);
console.log(config.retries);
console.log(settings.theme);
console.log(settings.debug);

const obj = { a: 1, b: 2, c: 3 };
const entries = Object.entries(obj);
const keys = Object.keys(obj);
const values = Object.values(obj);

const result = {
  entriesLength: entries.length,
  keysJoined: keys.join('-'),
  valuesSum: values.reduce((sum, val) => sum + val, 0),
  firstEntry: entries[0]
};

console.log(result.entriesLength);
console.log(result.keysJoined);
console.log(result.valuesSum);
console.log(result.firstEntry);

function* outer() {
  yield 1;
  yield* inner();
  yield 4;
}

function* inner() {
  yield 2;
  yield 3;
}

const gen = outer();
console.log(gen.next().value);
console.log(gen.next().value);
console.log(gen.next().value);
console.log(gen.next().value);

const user = {
  name: 'Sarah',
  age: 28,
  getName() {
    return this.name;
  }
};

const { getName } = user;
const boundGetName = user.getName.bind(user);

console.log(getName());
console.log(boundGetName());
console.log(user.getName());

function* fibonacci() {
  let a = 0, b = 1;
  yield a;
  yield b;
  while (true) {
    let next = a + b;
    yield next;
    a = b;
    b = next;
  }
}

const gen = fibonacci();
const results = [];
for (let i = 0; i < 6; i++) {
  results.push(gen.next().value);
}
console.log(results.join(','));

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);