Simple pub/sub TypeScript class for Angular

pubsub.ts

import { Injectable } from '@angular/core';

@Injectable({
  providedIn: 'root',
})
export class PubSub {
  private topics: { [id: string]: PubSubTopic } = {};

  private constructor() {}

  public static subscribe(topic: string, listener: (args: any) => void): void {
    this.getInstance().subscribeToTopic(topic, listener);
  }

  public static publish(topic: string, arg: any): void {
    this.getInstance().publishToTopic(topic, arg);
  }

  private static getInstance(): PubSub {
    if (!(window as any).myPubSub) {
      (window as any).myPubSub = new PubSub();
    }
    return (window as any).myPubSub;
  }

  private subscribeToTopic(topic: string, listener: (args: any) => void): void {
    this.getTopic(topic).subscribe(listener);
  }

  public publishToTopic(topic: string, arg: any): void {
    this.getTopic(topic).notify(arg);
  }

  private getTopic(name: string): PubSubTopic {
    if (!this.topics.hasOwnProperty(name)) {
      this.topics[name] = new PubSubTopic();
    }
    return this.topics[name];
  }
}

class PubSubTopic {
  public subscriptions: ((arg: object) => void)[];

  private lastArg: object | null = null;

  constructor() {
    this.subscriptions = [];
  }

  public subscribe(func: (arg: object) => void): void {
    this.subscriptions.push(func);
    // Publish the last event for this topic to the new subscription
    if (this.lastArg) {
      func(this.lastArg);
    }
  }

  public notify(arg: object): void {
    this.lastArg = arg;
    this.subscriptions.forEach((subscription) => {
      subscription(arg);
    });
  }
}