Publish-subscriber. Implementation of observer pattern in TypeScript.

Publisher.ts

type Subscriber<TData> = (data: TData) => void;

interface IPublisher<TEvent, TData> {
  subscribe(event?: TEvent): (subscriber: Subscriber<TData>) => () => void;
  notify(event: TEvent, data: TData): void;
}

export class Publisher<TEvent, TData> implements IPublisher<TEvent, TData> {
  protected subscribers: { event: TEvent; subscriber: Subscriber<TData> }[] = [];

  public subscribe = (event?: TEvent) => (subscriber: Subscriber<TData>) => {
    this.subscribers.push({ event, subscriber });
    return () => {
      this.subscribers = this.subscribers.filter(
        (sub) => subscriber !== sub.subscriber
      );
    };
  };

  public notify = (event: TEvent, data: TData) => {
    for (const sub of this.subscribers) {
      if (sub.event === event || !sub.event) {
        sub.subscriber(data);
      }
    }
  };
}