如何在TypeScript中使用观察者而不是主题来处理事件消息？

interface Observer {
  update(message: string): void;
}

class Subject {
  private observers: Observer[] = [];

  public registerObserver(observer: Observer): void {
    this.observers.push(observer);
  }

  public unregisterObserver(observer: Observer): void {
    const index = this.observers.indexOf(observer);
    if (index !== -1) {
      this.observers.splice(index, 1);
    }
  }

  public notifyObservers(message: string): void {
    for (const observer of this.observers) {
      observer.update(message);
    }
  }
}

class ConcreteObserver implements Observer {
  public update(message: string): void {
    console.log(`Received message: ${message}`);
    // 执行相应的操作
  }
}

const subject = new Subject();

const observer1 = new ConcreteObserver();
const observer2 = new ConcreteObserver();

subject.registerObserver(observer1);
subject.registerObserver(observer2);

subject.notifyObservers("Hello, observers!");

subject.unregisterObserver(observer2);

subject.notifyObservers("Another message");