custom JS pubsub

PubSub.ts

export interface IPubSubOptions {
  maxListeners?: number;
}

export class PubSub {
  private maxListeners: number;

  private listenerCount: number;

  private eventListeners: Map<string, Function[]>;

  constructor(options: IPubSubOptions) {
    this.maxListeners = options.maxListeners || 1000;
    this.listenerCount = 0;
  }

  setMaxListeners(listenerCount: number): PubSub {
    this.maxListeners = listenerCount;
    return this;
  }

  private setListenerCount(count: number): void {
    this.listenerCount = count;
  }

  getListenerCount(): number {
    return this.listenerCount;
  }

  getEventListenerCount(event: string): number {
    return (this.eventListeners.get(event) || []).length;
  }

  on(event: string, fn: Function): PubSub {
    if (this.getListenerCount() === this.maxListeners) {
      console.log('Number of listeners exceded maxListeners set');
      return this;
    }
    const listeners = this.eventListeners.get(event) || [];

    listeners.push(fn);
    this.eventListeners.set(event, listeners);
    this.setListenerCount(this.listenerCount + 1);
    return this;
  }

  off(event: string, fn: Function): PubSub {
    const listeners = this.eventListeners.get(event);

    if (!listeners) return this;

    const len = listeners.length;
    for (let i = 0; i < len; i++) {
      if (listeners[i] === fn) {
        listeners.splice(i, 1);
        this.setListenerCount(this.listenerCount - 1);
        break;
      }
    }

    return this;
  }

  once(event: string, fn: Function): PubSub {
    if (this.getListenerCount() === this.maxListeners) {
      console.log('Number of listeners exceded maxListeners set');
      return this;
    }
    const listeners = this.eventListeners.get(event) || [];

    const innerFn = (...args: IArguments[]) => {
      fn(...args);
      this.off(event, fn);
    };
    listeners.push(innerFn);

    this.eventListeners.set(event, listeners);
    this.setListenerCount(this.listenerCount + 1);
    return this;
  }

  emit(event: string, ...args: IArguments[]): boolean {
    const listeners = this.eventListeners.get(event);
    if (!listeners) return false;

    listeners.forEach(fn => fn(...args));

    return true;
  }
}

cont emitterOptions: IPubSubOptions = {
maxListeners: 10000,
}

const emitter = new PubSub(emitterOptions);
emitter.on('msg', (data) => console.log(data));
emitter.once('delete', (id) => console.log('deleted id'));

emitter.emit('msg', 'testing');