class EventEmitter {
  #listeners = new WeakMap();
  #registry = new FinalizationRegistry((label) => {
    console.log(`Cleaned up: ${label}`);
  });

  subscribe(target, callback) {
    if (!this.#listeners.has(target)) {
      this.#listeners.set(target, []);
    }
    this.#listeners.get(target).push(callback);
    this.#registry.register(target, target.name ?? "unknown");
  }

  emit(target) {
    const cbs = this.#listeners.get(target);
    if (cbs) cbs.forEach(cb => cb());
  }
}

const emitter = new EventEmitter();
let obj1 = { name: "sensor" };
let obj2 = { name: "timer" };

const ws = new WeakSet([obj1, obj2]);

emitter.subscribe(obj1, () => console.log("sensor fired"));
emitter.subscribe(obj2, () => console.log("timer fired"));
emitter.subscribe(obj1, () => console.log("sensor logged"));

emitter.emit(obj1);

console.log(ws.has(obj1));
obj1 = null;
console.log(ws.has({ name: "sensor" }));