A typed event emitter for TypeScript

event.ts

// This lets you emit and listen for events in a type-safe manner
// Awesome!

import { EventEmitter } from 'events'

type Type<Name> = { type: Name }
type Value<Type> = { value: Type }

export type TypedValue<T, V> = Type<T> & Value<V>

// These are some examples of typed events. One expects a string payload, and the other a number.
// You can add your custom events here!
export type EventOne = TypedValue<'EventOne', { payload: string }>
export type EventTwo = TypedValue<'EventTwo', { payload: number }>

type Types = EventOne | EventTwo

const bus: EventEmitter = new EventEmitter()

// Call on() to listen to an event
export const on = <T extends Types> (type: Pick<T, 'type'>, listener: (value: T) => void) => {
  console.log('registering event handler for type', type.type)
  bus.addListener(type.type, listener)
}

// Call emit() to publish a specific type of event
export const emit = <T extends Types> (type: T) => {
  console.log('emitting event of type', type.type)
  bus.emit(type.type, type)
}