Enum module augmentation

event-bus-consumer.ts

import { Event, Payload, bus } from './event-bus'

// Module augmentation here
declare module './event-bus' {
  interface Event {
    SIGN_IN: 'SIGN_IN'
    SIGN_OUT: 'SIGN_OUT'
  }

  interface Payload {
    SIGN_IN: string
  }
}

bus.emit('SIGN_OUT') // Valid TS
bus.emit('SIGN_IN', 1) // Argument of type 'number' is not assignable to parameter of type 'string'.

event-bus.ts

export interface Event {
  NOTIFY: 'NOTIFY'
}

export interface Payload {
  NOTIFY: string
}

export type EventName = Event[keyof Event]
export type EventPayload<E> = E extends keyof Payload ? Payload[E] : unknown

type EventBus = {
  subscribe<E extends EventName>(e: E, cb: (e: EventPayload<E>) => void): void
  emit<E extends EventName>(e: E, payload: EventPayload<E>): void
  emit<E extends EventName>(e: E): void
}

export const bus: EventBus = {
  emit(e, payload?): void {
  },
  subscribe(e, cb) {
    // Subscribe implementation
  }
}