const secretKey = Symbol('key');
const secretValue = 'secret';

function Store() {
  this[secretKey] = secretValue;
}

Store.prototype.get = function(key) {
  return this[key];
};

const store = new Store();
const revealed = store.get(secretKey);
console.log(revealed);

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

async function asyncFunc() {
  for (let value of gen()) {
    await new Promise(res => setTimeout(res, 100));
    console.log(value);
  }
  return 'done';
}

const result = asyncFunc();
console.log(result instanceof Promise);

const handler = {
  get(target, prop, receiver) {
    if (prop === 'secret') {
      return Reflect.get(...arguments) + ' exposed';
    }
    return Reflect.get(...arguments);
  }
};

const secretObj = { secret: 'hidden', reveal: 'nothing' };
const proxy = new Proxy(secretObj, handler);

console.log(proxy.secret);

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

const gen = generator();
const sym = Symbol('unique');

gen[sym] = function() {
  return this.next().value;
};

console.log(gen[sym](), gen[sym](), gen[sym]());

const func = new Function('a', 'b', 'return a + b');
console.log(func(1, 2));

function* generator() {
  yield 1;
  yield* [2, 3];
  yield 4;
}

const gen = generator();

const arr = Array.from(gen);
console.log(arr);

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

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

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