WeakMap, WeakSet, Proxy, Reflect

const wm = new WeakMap();

let user = { name: "রহিম" };
wm.set(user, "active");

console.log(wm.get(user)); // "active"

// user-কে মুছে দিলে entry গার্বেজ-কুড়ির সুযোগ
user = null;

// WeakMap: key অবশ্যই object — string নয়

// object-সংগত private/extra data
const meta = new WeakMap();

class Player {
  constructor(name) {
    this.name = name;
    meta.set(this, { score: 0 });
  }
  addScore(points) {
    meta.get(this).score += points;
  }
  getScore() {
    return meta.get(this).score;
  }
}

const p = new Player("রহিম");
p.addScore(10);
console.log(p.getScore()); // 10

const ws = new WeakSet();

let obj = {};
ws.add(obj);

console.log(ws.has(obj)); // true

obj = null;
// WeakSet-থেকে object নিজে-নিজে সরে যায়

const ref = new WeakRef({ data: "কিছু" });

// deref() — object বেঁচে থাকলে দেয়, নাহলে undefined
const value = ref.deref?.();
console.log(value?.data);

const target = { name: "রহিম" };

const proxy = new Proxy(target, {
  get(obj, prop) {
    if (!(prop in obj)) {
      return `অজানা: ${prop}`;
    }
    return obj[prop];
  },
  set(obj, prop, value) {
    if (prop === "age" && (typeof value !== "number" || value < 0)) {
      throw new Error("invalid age");
    }
    obj[prop] = value;
    return true;
  },
});

console.log(proxy.name);          // রহিম
console.log(proxy.nonexistent);   // অজানা: nonexistent

proxy.age = 25;
console.log(proxy.age);
// proxy.age = -5;  // Error

const user = { name: "রহিম" };
const proxy2 = new Proxy(user, {
  get(obj, prop) {
    console.log(`অ্যাক্সেস: ${prop}`);
    return obj[prop];
  },
});

console.log(proxy2.name);
// অ্যাক্সেস: name
// রহিম

const target = { a: 1 };

const proxy3 = new Proxy(target, {
  get(obj, prop, receiver) {
    return Reflect.get(obj, prop, receiver) ?? "নেই";
  },
});

console.log(proxy3.a);   // 1
console.log(proxy3.zzz); // নেই