const sym1 = Symbol('test');
const sym2 = Symbol('test');
const obj = {
  [sym1]: 'first',
  [sym2]: 'second',
  regular: 'third'
};

const keys = Object.keys(obj);
const symbols = Object.getOwnPropertySymbols(obj);
const allProps = Reflect.ownKeys(obj);

console.log(keys.length);
console.log(symbols.length);
console.log(allProps.length);
console.log(sym1 === sym2);

const sym1 = Symbol('test');
const sym2 = Symbol('test');
const obj = {
  [sym1]: 'first',
  [sym2]: 'second',
  regular: 'third'
};

const keys = Object.keys(obj);
const symbols = Object.getOwnPropertySymbols(obj);
const allProps = Reflect.ownKeys(obj);

console.log(keys.length);
console.log(symbols.length);
console.log(allProps.length);
console.log(sym1 === sym2);

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;
  
  const counter = {
    increment() {
      count++;
      return count;
    },
    getCount() {
      return count;
    }
  };
  
  return counter;
}

let c1 = createCounter();
c1.increment();
c1.increment();

let c2 = c1;
c1 = null;

console.log(c2.getCount());

const arr = [1, 2, 3, 4, 5];
const result = arr
  .map(x => x * 2)
  .filter(x => x > 5)
  .reduce((acc, val) => {
    return acc + (val % 3 === 0 ? val : 0);
  }, 0);

console.log(result);

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();

let x = 5;

function foo() {
  console.log(x);
  let x = 10;
  console.log(x);
}

foo();

const team = {
  members: ['Alice', 'Bob', 'Charlie'],
  [Symbol.iterator]: function*() {
    let index = 0;
    while(index < this.members.length) {
      yield this.members[index++].toUpperCase();
    }
  }
};

const result = [];
for (const member of team) {
  result.push(member);
}

console.log(result.join('-'));

const obj = {};
let value = 0;

Object.defineProperty(obj, 'prop', {
  get() {
    return value;
  },
  set(newValue) {
    value = newValue + 1;
  },
  configurable: true,
  enumerable: true
});

obj.prop = 10;
console.log(obj.prop);

const a = async () => {
   return Promise.reject('rejected');
};

a().catch(error => console.log(error));
console.log('done');

const map = new WeakMap();

let obj1 = { name: 'user1' };
let obj2 = { name: 'user2' };

map.set(obj1, 'data for user1');
map.set(obj2, 'data for user2');

console.log(map.has(obj1));
obj1 = null;

console.log(map.has(obj1));
console.log(map.get(obj2));

function Person(name) {
  this.name = name;
  this.sayName = () => console.log(this.name);
}

const person1 = new Person('David');
const person2 = { name: 'Not David', sayName: person1.sayName };

person2.sayName();

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* 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);