如何在TypeScript中实现发布-订阅模式？

// Step 1: 创建主题类
class Subject {
  private observers: Observer[] = [];

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

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

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

// Step 2: 创建观察者接口或基类
interface Observer {
  update(): void;
}

// Step 3: 创建具体的观察者类
class ConcreteObserver implements Observer {
  private subject: Subject;

  constructor(subject: Subject) {
    this.subject = subject;
  }

  public update(): void {
    // 处理主题通知的逻辑
    console.log('Received notification from subject.');
  }
}

// Step 4: 订阅主题
const subject = new Subject();
const observer = new ConcreteObserver(subject);
subject.subscribe(observer);

// 发布通知
subject.notify();