class EventManager {
  constructor() {
    this.listeners = new Map();
  }
  
  addListener(event, callback) {
    if (!this.listeners.has(event)) {
      this.listeners.set(event, new Set());
    }
    this.listeners.get(event).add(callback);
  }
  
  removeListener(event, callback) {
    this.listeners.get(event)?.delete(callback);
  }
}

const manager = new EventManager();
const handler = () => console.log('handled');
manager.addListener('click', handler);
manager.removeListener('click', () => console.log('handled'));
console.log(manager.listeners.get('click').size);