strict-mrs-mitt 🙋

This is a minimalist event-emitter, written in Typescript, providing type safety, where some preexisting solutions bail out.

Installation

Install it via npm

npm i -S strict-mrs-mitt

Usage

Just import the class constructor

import {StrictMrsMitt} from 'strict-mrs-mitt'

if using Typescript describe events and their arguments in a type. One simple example how to type your events and the arguments they emit:

type EventMap = {
  done: () => void;
  greet: (name: string) => void;
  greetCouple: (name1: string, name2: string) => void;
};

Pass the types to the emitter on initialization:

const emitter = new StrictMrsMitt<EventMap>()

Registering and unregistering listeners

Listeners can be registered via the on method:

emitter.on('done', ()=>console.log("I'm done")

Listeners, that should unregister after they listen do some event once can be registered using the once method:

emitter.once('done', ()=>console.log("I'm done")

All event listeners can be removed manually using the off method.

emitter.off('done', someHandler)

Emitting Events

To emit a particular event, use the emit method and pass the right argument.

emitter.emit('greet', 'peter')

Typesafety

If the emitter is passed types of events and listeners on initialization, Typescript will register if you emit events without passing the right arguments. Examples:

type EventMap = {
 done: () => void;
 greet: (name: string) => void;
 greetCouple: (name1: string, name2: string) => void;
};
const emitter = new StrictMrsMitt<EventMap>()
// the following won't work, because 'done' does not emit the string, the registered callback expects
emitter.on('done', (name: string)=>console.log(`hello, ${name}`)
// the next example will also cause a compiler warning, since the done event won't emit the string passed to it
emitter.emit('done', 'unexpexted string arg')

Contributing

Pull requests are welcome. For major changes, please open an issue first to discuss what you would like to change.

Please make sure to update tests as appropriate.

License

MIT