const sym1 = Symbol('sym');
const sym2 = Symbol('sym');

const obj = {
  [sym1]: 'value1',
  [sym2]: 'value2'
};

console.log(obj[sym1], obj[sym2], sym1 === sym2);

function* generator() {
  yield 1;
  yield 2;
  yield 3;
}

const gen = generator();

const { value, done } = gen.return('early');

console.log(value, done);

const sym = Symbol('unique');
const obj = {
  [sym]: 'symbol value',
  a: 1,
  b: 2
};

const keys = Object.keys(obj);
const symbols = Object.getOwnPropertySymbols(obj);

console.log(keys.length, symbols.length);

const obj = {
  value: 1,
  method() {
    return this.value;
  }
};

const boundMethod = obj.method.bind({ value: 2 });
console.log(boundMethod());

const obj1 = { a: 1 };
const obj2 = { b: 2 };
Object.setPrototypeOf(obj2, obj1);

console.log('a' in obj2);
console.log(obj2.hasOwnProperty('a'));
console.log(obj2.__proto__.a);

async function asyncFunc() {
  return 'async';
}

function promiseFunc() {
  return new Promise(resolve => resolve('promise'));
}

(async function() {
  const result = await (true ? asyncFunc() : promiseFunc());
  console.log(result);
})();

const obj1 = {
  a: 1,
  method() {
    return this.a;
  }
};

const obj2 = Object.create(obj1);
obj2.a = 2;

console.log(obj2.method());