pub-sub EventEmitter

EventEmitter.ts

type EventCallback<Opts extends unknown = any> = Opts extends undefined
  ? (opts?: undefined) => void
  : (opts: Opts) => void;

class EventEmitter<EventType = string> {
  private listeners: Map<EventType, Array<EventCallback>>;

  constructor() {
    this.listeners = new Map();
    this.addListeners = this.addListeners.bind(this);
    this.emit = this.emit.bind(this);
  }

  addListeners(type: EventType, callback: EventCallback) {
    const callbacks = this.listeners.get(type) ?? [];
    const alreadyListening = callbacks.some((cb) => cb === callback);

    if (!alreadyListening) {
      callbacks.push(callback);
      this.listeners.set(type, callbacks);
    }
  }

  removeListeners(type: EventType, callback: EventCallback) {
    const callbacks = this.listeners.get(type) ?? [];
    const filteredCallbacks = callbacks.filter((cb) => cb !== callback);

    if (callbacks.length !== filteredCallbacks.length) {
      this.listeners.set(type, filteredCallbacks);
    }
  }

  emit(type: EventType, opts?: unknown) {
    const callbacks = this.listeners.get(type) ?? [];
    callbacks.forEach((callback) => callback(opts));
  }
}

export { type EventCallback };
export default EventEmitter;