TypedEventTarget

Strictly typed EventTarget that directly extends EventTarget to function as a drop-in replacement. It works with all Event-Types and accounts for basically no additional bundle-size.

Motivation

Since EventTarget support landed in NodeJS v14.5, they are the only way to go forward, when talking about event driven JS.
But EventTarget lacks in terms of developer experience and Typescript integration. To be specific:

• No strictly typed event listeners & events
• Missing proper IntelliSense integration
• No auto-complete for event types

The weird thing is, that with JS-native objects, which implement EventTarget (like WebSocket, Worker or any HTML-Elements), you get all those features out of the box:

This package aims to fix these shortcomings and add all these missing features for custom EventTargets.

Installation

NPM

Install the package:

npm i --save typescript-event-target

Then import as follows:

import { TypedEventTarget } from 'typescript-event-target';

Deno

Either install from JSR:

deno add @derzade/typescript-event-target

or import directly form deno.land/x/:

import { TypedEventTarget } from 'https://deno.land/x/typescript_event_target/mod.ts';

⚠️ Warning: It is best practice to “pin” to a particular version. https://deno.land/x/ supports using git tags in the URL to direct you at a particular version. So to use version 1.0.0 of TypedEventTarget, you would want to import https://deno.land/x/typescript_event_target@v1.0.0/mod.ts.

Usage

1. Basic Example
2. Dispatching Events
3. Extending TypedEventTarget
4. Different Event Types

Basic Example

// Step 1: Create an interface, which
// includes all dispatchable events
interface MyEventMap {
    hello: Event;
    time: CustomEvent<number>;
}

// Step 2: Create your TypedEventTarget, with
// the EventMap as the type parameter
const eventTarget = new TypedEventTarget<MyEventMap>();

// Step 3: Strictly typed EventListeners 🎉
eventTarget.addEventListener('time', (event) => {
    // event is of type CustomEvent<number>

    const time = event.detail;

    // time is of type number
});

Dispatching Events

TypedEventTarget directly extends EventTarget, so dispatchEvent works as expected, but is marked as deprecated. The reason for this is that dispatchEvent cannot be strictly typed easily. Instead, TypedEventTarget introduces a dispatchTypedEvent method, which is strictly typed by taking an additional _type parameter (just used for type checking).

interface MyEventMap {
    time: CustomEvent<number>;
}

const eventTarget = new TypedEventTarget<MyEventMap>();

eventTarget.dispatchTypedEvent(
    'time',
    new CustomEvent('time', { detail: Date.now() })
);

Extending TypedEventTarget

Instead of directly instantiating TypedEventTarget, you can also extend it:

interface MyEventMap {
    time: CustomEvent<number>;
    // [...]
}

class MyEventTarget extends TypedEventTarget<MyEventMap> {
    /* [...] */
}

const myTarget = new MyEventTarget();
myTarget.addEventListener('time', (e) => {
    /* [...] */
});

Different Event Types

Your EventMap can include Event as well as any type, that extends Event. These can be native Events or even own classes:

class MyEvent extends Event {
    /* [...] */
}

class MyEventMap {
    boring: Event;
    custom: CustomEvent<number>;
    mine: MyEvent;
    mouse: MouseEvent;
    keyboard: KeyboardEvent;
}

const eventTarget = new TypedEventTarget<MyEventMap>();

eventTarget.addEventListener('mine', (e) => {
    // e is of type MyEvent
});

Bundle Size

This package mostly only contains TypeScript definitions. Therefore, it amounts up to basically no bundle size. The only thing that is bundled is the dispatchTypedEvent-method, which is just a simple wrapper around the native dispatchEvent-method.