slorber / micro-typed-events

The smallest, most convenient typesafe TS event emitter you'll ever need

micro-typed-events

const events = createEvents<number>();
const unsubscribe = events.subscribe(num => console.log(num));
events.emit(42);
events.emit(57);
unsubscribe();

events.emit(99); // not logged
events.emit('hey'); // not compiling

The smallest, most convenient, typesafe (with TS, but also works with normal JS), event emitter / pubsub system you'll ever need.

Unlike other event emitters, it does not use on/off/once methods but only a single subscribe method and returns an unsubscribe handle, which makes it more tiny, easier to type, more convenient to use with arrow functions.

The most minimal code you need for a typesafe pub/sub system, and feature complete, making suitable to include as a dependency on other libraries.

Install

npm install --save micro-typed-events
// or
yarn add micro-typed-events

Usage

Simple typed events

import { createEvents } from 'micro-typed-events';

const events = createEvents<number>();

const unsubscribe = events.subscribe(num => console.log(num));

events.emit(42);
events.emit('hey'); // Does not compile

unsubscribe();

---

Object typed events

import { createEvents } from 'micro-typed-events';

type EventType = { num: number; str: string };
const events = createEvents<EventType>();

const unsubscribe = events.subscribe(obj => console.log(obj));

events.emit({ num: 42, str: 'hello' });
events.emit({ num: 42, str: null }); // Does not compile

unsubscribe();

---

Multiple-args typed events

import { createEvents } from 'micro-typed-events';

const events = createEvents<number, string>();

const unsubscribe = events.subscribe((num, str) => console.log(num, str));

events.emit(42, 'hello');
events.emit('hello', 42); // Does not compile

unsubscribe();

---

Advanced typing, dynamic args...

import { createEvents } from 'micro-typed-events';

// Listener type is any void function
type ListenerType = (str: string, num: number, ...args: any[]) => void;

const events = createEvents<ListenerType>();

const unsubscribe = events.subscribe((str, num, ...args) =>
  console.log(str, num, ...args),
);

events.emit('hey', 1, 'blaa', 'whatever', 'you', 'want', 1, 2, 3);
events.emit(1, 'hey', 'blaa', 'whatever', 'you', 'want', 1, 2, 3); // Does not compile

unsubscribe();

---

Vanilla JS

import { createEvents } from 'micro-typed-events';

const events = createEvents();

const unsubscribe = events.subscribe(num => console.log(num));

events.emit(42);
events.emit('hey'); // Does not fail, you should use typescript

unsubscribe();

FAQ

Should I create a single events object for all my events?

No, you should rather create one per event-type. You could expose all your events as an object, like this:

export const ApiEvents = {
  requests: createEvents<Request>(),
  responses: createEvents<Response>(),
  errors: createEvents<Errors>(),
};

Can I unsubscribe directly inside a listener

Yes, listeners are able to unsubscribe themselves (or other listeners) without messing things up.

Can I subscribe directly inside a listener

Yes, but that listener will only be called on next emitted event.

Can I embed this library in my library?

Yes, this lib is very tiny. It exports ES and CJS modules. Here's the CJS output, I'll let you judge yourself if you can write something shorter:

'use strict';

Object.defineProperty(exports, '__esModule', { value: true });

function createEvents() {
    var listeners = [];
    return {
        subscribe: function (listener) {
            listeners.push(listener);
            return function () {
                var index = listeners.indexOf(listener);
                if (index > -1) {
                    listeners.splice(index, 1);
                }
            };
        },
        emit: function () {
            var args = [];
            for (var _i = 0; _i < arguments.length; _i++) {
                args[_i] = arguments[_i];
            }
            // take care of user trying to unsub inside a listener
            listeners.slice().forEach(function (listener) {
                if (listeners.indexOf(listener) > -1) {
                    listener.apply(void 0, args);
                }
            });
        },
    };
}

exports.createEvents = createEvents;
//# sourceMappingURL=index.js.map

License

MIT © slorber

Hire a freelance expert

Looking for a React/ReactNative freelance expert with more than 5 years production experience? Contact me from my website or with Twitter.