Observer & Singleton Patterns

How should you implement an Observer Pattern for handling asynchronous events?

class AsyncSubject {
  constructor() {
    this.observers = new Set();
  }

  subscribe(observer) {
    this.observers.add(observer);
    return () => this.observers.delete(observer);
  }

  async notify(data) {
    const notifications = Array.from(this.observers)
      .map(observer => observer.update(data));
    await Promise.all(notifications);
  }
}

class AsyncObserver {
  async update(data) {
    // Handle async update
    await processData(data);
  }
}

Async operations should be avoided in observers
The notify method shouldn't be async
Each observer should handle its own async operations independently
The implementation correctly handles async notifications
This implementation correctly handles asynchronous events in the Observer Pattern by: 1) Using async/await for the notify method, 2) Handling Promise.all to wait for all observer updates, 3) Allowing observers to perform async operations, and 4) Using a Set to manage unique observers. This approach ensures proper handling of asynchronous updates while maintaining the pattern's structure.

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