create-typed-emitter

Very simple typed event emitter with a simplified api interface, inspired by strict-event-emitter-types

Features

• Very simple api, on, once, off, fire and clear methods
• The on, once, off and fire methods are typed, so you can be sure that the event you are listening to is of the type you expect and receive the correct payload
• The on, once methods returns a function that you can use to remove the listener without having to pass the event name and the listener function

Installation

npm install create-typed-emitter

Usage

import { createEmitter } from 'create-typed-emitter';
// create an interface for your emitter events
interface EmitterInterface {
  event: { foo: string; bar: number };
  // other events signatures come here
}

const emitter = createEmitter<EmitterInterface>();

// typescript will complain if you try to fire an event that doesn't exist
// typescript will complain if the payload is not of the correct type
emitter.on('event', ({ foo, bar }) => {
  console.log(foo, bar);
});

// this will fail as the event listened does not exist in the typed interface
emitter.on('foo', ({ foo, bar }) => {
  console.log(foo, bar);
});

// this will work, the event fired is of the correct type and have the correct payload
emitter.fire('event', { foo: 'bar', bar: 1 });

// this will fail because bar is missing
emitter.fire('event', { foo: 'bar' });

// this will fail because foo is not a string
emitter.fire('event', { foo: 1, bar: 1 });

// this will fail because the emitted event does not exist
emitter.fire('foo', { foo: 'bar', bar: 1 });

// this will execute the listener only once
emitter.once('event', ({ foo, bar }) => {
  console.log(foo, bar);
});

// this will remove the listener added without referencing the listener function
const off = emitter.once('event', ({ foo, bar }) => {
  console.log(foo, bar);
});

// later remove the listener (useful in useEffect cleanup in React for example)
off();

License

MIT