Publish-subscribe pattern

event-emitter.ts

type EventHandler = (...args: any[]) => any;

class EventEmitter {
  private c = new Map<string, EventHandler[]>();

  subscribe(topic: string, ...handlers: EventHandler[]) {
    let topics = this.c.get(topic);
    if (!topics) {
      this.c.set(topic, (topics = []));
    }
    topics.push(...handlers);
  }

  unsubscribe(topic: string, handler?: EventHandler): boolean {
    if (!handler) {
      return this.c.delete(topic);
    }

    const topics = this.c.get(topic);
    if (!topics) {
      return false;
    }

    const index = topics.indexOf(handler);

    if (index < 0) {
      return false;
    }
    topics.splice(index, 1);
    if (topics.length === 0) {
      this.c.delete(topic);
    }
    return true;
  }

  publish(topic: string, ...args: any[]): any[] | null {
    const topics = this.c.get(topic);
    if (!topics) {
      return null;
    }
    return topics.map((handler) => {
      try {
        return handler(...args);
      } catch (e) {
        console.error(e);
        return null;
      }
    });
  }
}