bknd/app/src/core/events/Event.ts

export type EventClass = {
   new (params: any): Event<any, any>;
   slug: string;
};

export abstract class Event<Params = any, Returning = void> {
   _returning!: Returning;

   /**
    * Unique event slug
    * Must be static, because registering events is done by class
    */
   static slug: string = "untitled-event";
   params: Params;
   returned: boolean = false;

   /**
    * Shallow validation of the event return
    * It'll be deeply validated on the place where it is called
    */
   validate(value: Returning): Event<Params, Returning> | void {
      throw new EventReturnedWithoutValidation(this as any, value);
   }

   protected clone<This extends Event<Params, Returning> = Event<Params, Returning>>(
      this: This,
      params: Params,
   ): This {
      const cloned = new (this.constructor as any)(params);
      cloned.returned = true;
      return cloned as This;
   }

   constructor(params: Params) {
      this.params = params;
   }
}

// @todo: current workaround: potentially there is "none" and that's the way
export class NoParamEvent extends Event<null> {
   static override slug: string = "noparam-event";

   constructor() {
      super(null);
   }
}

export class InvalidEventReturn extends Error {
   constructor(expected: string, given: string) {
      super(`Expected "${expected}", got "${given}"`);
   }
}

export class EventReturnedWithoutValidation extends Error {
   constructor(
      event: EventClass,
      public data: any,
   ) {
      // @ts-expect-error slug is static
      super(`Event "${event.constructor.slug}" returned without validation`);
   }
}