const a = { value: 1 };
const b = Object.create(a);
b.value = 2;

console.log(b.value);
console.log(a.value);

let count = 0;

const counter = (function() {
  count = 0;
  return function() {
    count += 1;
    return count;
  };
})();

count = 10;
counter();
console.log(count);

const target = {
  age: 30
};

const handler = {
  get: function(obj, prop) {
    return obj[prop]++;  
  }
};

const proxy = new Proxy(target, handler);

console.log(proxy.age);
console.log(target.age);
console.log(proxy.age);

let obj1 = { key: 'value1' };
let obj2 = { key: 'value2' };

const weakMap = new WeakMap();
weakMap.set(obj1, 'data1');
weakMap.set(obj2, 'data2');

obj1 = null;
setTimeout(() => {
  console.log(weakMap.has(obj1));
  console.log(weakMap.has(obj2));
}, 100);

const target = {
  secret: "hidden",
  reveal: "nothing"
};

const handler = {
  get: function(obj, prop, receiver) {
    if (prop === "secret") {
      return "revealed";
    }
    return Reflect.get(...arguments);
  }
};

const proxy = new Proxy(target, handler);

with (proxy) {
  console.log(secret);
  console.log(reveal);
}

function* numberDoubler(arr) {
  for (const num of arr) {
    yield num * 2;
  }
}

const result = [...numberDoubler([1, 2, 3])].some(n => n % 4 === 0);

console.log(result);