@mizdra/strictly-typed-event-target

This is a strictly-typed version of EventTarget.

Motivation

Traditionally, there was no universal native event emitter for browsers and Node.js. Therefore, if you wanted a universal event emitter that worked in both environments, you had to use a 3rd-party library like eventemitter3. However, recently, Node.js has implemented EventTarget (An experimental feature not yet available to the public as of 2020/09), EventTarget is establishing itself as a universal event emitter.

Because EventTarget is a native API, it's smaller than a 3rd party library like eventemitter3 (rather than needing an extra bundle!). However, EventTarget cannot restrict the types of events it dispatches like eventemitter3. This has the problem that unexpected events of type is dispatched , may cause runtime errors.

Therefore, @mizdra/strictly-typed-event-target provides EventTarget, which can restrict the types of events to be dispatched. It's based on EventTarget and CustomEvent, so it's very small in size.

Feature

• Based on EventTarget and CustomEvent
• Strictly-typed API
  • Restrict the types of events to be dispatched with EventMap
• Universal
  • Work in the browser/Node.js in the future (NOTE: not supported in some environments yet)
• Standardized API
  • EventTarget and CustomEvent are standardized by WHATWG (ref: spec)
• VERY VERY small size
  • ES Module version size is 1XX B. (ref: source)

Install

$ npm install -S @mizdra/strictly-typed-event-target
$ yarn add @mizdra/strictly-typed-event-target

Usage

import { createSTEventTarget } from '@mizdra/strictly-typed-event-target';

// First, you should define event for `EventTarget`.
interface FooEventMap {
  // `onmessage` is event name, and `string` is type of `CustomEvent#detail`.
  onmessage: string;
  onerror: Error;
  oninstall: undefined;
}

// `createSTEventTarget` is a utility for creating
// strictly-typed `CustomEvent` and `EventTarget`.
const [FooCustomEvent, FooEventTarget] = createSTEventTarget<FooEventMap>();
const fooEventTarget = new FooEventTarget();

// `addEventListener`
fooEventTarget.addEventListener('onmessage', (event) => {
  // `event.detail` is infered `string` type.
});
fooEventTarget.addEventListener('onerror', (event) => {
  // `event.detail` is infered `Error` type.
});

// `dispatchEvent`
fooEventTarget.dispatchEvent(
  new FooCustomEvent('onmessage', { detail: 'hello' })
);
// compile error
fooEventTarget.dispatchEvent(
  new FooCustomEvent('onmessage', { detail: new Error() }),
);
fooEventTarget.dispatchEvent(new FooCustomEvent('oninstall'));

// `removeEventListener`
const listener: STEventListenerOrEventListenerObject<
  FooEventMap,
  'onmessage',
> = () => {};
fooEventTarget.addEventListener('onmessage', listener);
fooEventTarget.removeEventListener('onmessage', listener);

APIs

ref: src/index.ts

Compatibility

Apart from the type definition, they are identical to EventTarget CustomEvent, so the compatibility with them is the same. See MDN or Node.js API Documents for details.

• Browser
  • EventTarget: https://developer.mozilla.org/en-US/docs/Web/API/EventTarget#Browser_compatibility
  • CustomEvent: https://developer.mozilla.org/en-US/docs/Web/API/CustomEvent#Browser_compatibility
• Node.js
  • EventTarget: https://nodejs.org/api/events.html#events_eventtarget_and_event_api
  • CustomEvent: not implemented yet

How to develop (for Contributor)

• yarn run start: Run for production
• yarn run build: Build for production
• yarn run dev: Run for development
• yarn run check: Try static-checking

How to release (for Contributor)

$ # Wait for passing CI...
$ git switch master
$ git pull
$ yarn version
$ npm run build
$ npm publish
$ git push --follow-tags