Different patterns for listening/subscribing to events within a class

eventSubscriber.ts

export type Subscriber = (event: YourEvent) => void;

/**
 * When you have specific events and want to use a subscriber pattern.
 */
class WithEventSubscribers {
  private _subscribers: Partial<{ [type in YourEventTypes]: Subscriber[] }>;
    
  constructor() {
    this._subscribers = {};  
  }

  subscribe(type: YourEventTypes, subscriber: Subscriber) {
    (this._subscribers[type] ?? (this._subscribers[type] = [])).push(subscriber);
    return this._removeSubscriber(type, subscriber);
  }

  private _removeSubscriber(type: YourEventTypes, subscriber: Subscriber) {
    return () => this._subscribers[type] = this._subscribers[type]?.filter(s => s !== subscriber);
  }
}
    
// To use:

const subscriber = (e: YourEvent) => console.log(e);

const withSubscribers = new WithEventSubscribers();

const unsubscribe = withSubscribers.subscribe('some-event-type', subscriber);

// Later...

unsubscribe()

listeners.ts

export type EventListener = (event: YourEvent) => void;

/**
 * When you have specific events and want to use an event listener pattern.
 */
class WithEventListeners {
  private _eventListeners: Partial<{ [type in YourEventTypes]: EventListener[] }>;
    
  constructor() {
    this._eventListeners = {};  
  }

  addEventListener(type: YourEventTypes, listener: EventListener) {
    (this._eventListeners[type] ?? (this._eventListeners[type] = [])).push(listener);
  }

  removeEventListener(type: YourEventTypes, listener: EventListener) {
    this._eventListeners[type] = this._eventListeners[type]?.filter(l => l !== listener);
  }
}
    
// To use:

const eventListener = (e: YourEvent) => console.log(e);

const withEventListeners = new WithEventListeners();

withEventListeners.addEventListener('some-event-type', eventListener);

// Later...

withEventListeners.removeEventListener('some-event-type', eventListener);

simpleSubscriber.ts

export type Subscriber = () => void;

/**
 * When you don't have specific events, just one thing to subscribe to.
 */
class WithSimpleSubscribers {
  private _subscribers: Subscriber[];
    
  constructor() {
    this._subscribers = [];  
  }

  subscribe(subscriber: Subscriber) {
    this._subscribers.push(subscriber);
    return this._removeSubscriber(subscriber);
  }

  private _removeSubscriber(subscriber: Subscriber) {
    return () => this._subscribers.filter(s => s !== subscriber);
  }
}
    
// To use:

const subscriber = () => console.log('fired');

const withSubscribers = new WithSimpleSubscribers();

const unsubscribe = withSubscribers.subscribe(subscriber);

// Later...

unsubscribe()