tiny-typed-emitter

What is tiny-typed-emitter?

The tiny-typed-emitter package is a lightweight, strongly-typed event emitter for TypeScript and JavaScript. It allows you to create and manage events with type safety, ensuring that event listeners and emitters are correctly typed.

What are tiny-typed-emitter's main functionalities?

Basic Event Emission

This feature allows you to define and emit events with specific types. The code sample demonstrates how to create a custom event emitter, add listeners for 'data' and 'error' events, and emit those events with the appropriate data types.

const { TypedEmitter } = require('tiny-typed-emitter');

class MyEmitter extends TypedEmitter {
  // Define event types
  on(event: 'data', listener: (data: string) => void): this;
  on(event: 'error', listener: (error: Error) => void): this;
}

const emitter = new MyEmitter();

// Add listeners
emitter.on('data', (data) => {
  console.log('Data received:', data);
});

emitter.on('error', (error) => {
  console.error('Error occurred:', error);
});

// Emit events
emitter.emit('data', 'Hello, World!');
emitter.emit('error', new Error('Something went wrong!'));

Removing Event Listeners

This feature allows you to remove event listeners. The code sample demonstrates how to add a listener for the 'data' event, emit the event, remove the listener, and then emit the event again to show that the listener has been removed.

const { TypedEmitter } = require('tiny-typed-emitter');

class MyEmitter extends TypedEmitter {
  on(event: 'data', listener: (data: string) => void): this;
}

const emitter = new MyEmitter();

function onData(data) {
  console.log('Data received:', data);
}

// Add listener
emitter.on('data', onData);

// Emit event
emitter.emit('data', 'Hello, World!');

// Remove listener
emitter.off('data', onData);

// Emit event again (no output expected)
emitter.emit('data', 'Hello again!');

Once Event Listeners

This feature allows you to add a listener that will be called only once. The code sample demonstrates how to add a 'once' listener for the 'data' event, emit the event to trigger the listener, and then emit the event again to show that the listener is not called a second time.

const { TypedEmitter } = require('tiny-typed-emitter');

class MyEmitter extends TypedEmitter {
  on(event: 'data', listener: (data: string) => void): this;
  once(event: 'data', listener: (data: string) => void): this;
}

const emitter = new MyEmitter();

// Add a once listener
emitter.once('data', (data) => {
  console.log('Data received:', data);
});

// Emit event (listener will be called)
emitter.emit('data', 'Hello, World!');

// Emit event again (listener will not be called)
emitter.emit('data', 'Hello again!');

Other packages similar to tiny-typed-emitter

eventemitter3

EventEmitter3 is a high-performance event emitter for Node.js and the browser. It is similar to tiny-typed-emitter but does not provide built-in TypeScript support. You can use TypeScript with EventEmitter3, but you will need to define your own type definitions.

mitt

Mitt is a tiny, functional event emitter. It is similar to tiny-typed-emitter in terms of size and simplicity but does not offer built-in TypeScript support. Mitt is designed to be extremely lightweight and fast.

node-event-emitter

Node-Event-Emitter is a simple and lightweight event emitter for Node.js. It is similar to tiny-typed-emitter but does not provide type safety. It is a good choice if you need a basic event emitter without the overhead of type definitions.

README

tiny-typed-emitter

Have your events and their listeners type-checked with no overhead.

Install

Simply add the dependency using npm:

$ npm i tiny-typed-emitter

or using yarn:

$ yarn add tiny-typed-emitter

Usage

1. import tiny-typed-emitter library:

import { TypedEmitter } from 'tiny-typed-emitter';

1. define events and their listener signatures (note: quotes around event names are not mandatory):

interface MyClassEvents {
  'added': (el: string, wasNew: boolean) => void;
  'deleted': (deletedCount: number) => void;
}

1. on this step depending on your use case, you can:

• define your custom class extending EventEmitter:

  class MyClass extends TypedEmitter<MyClassEvents> {
    constructor() {
      super();
    }
  }
  

• create new event emitter instance:

  const emitter = new TypedEmitter<MyClassEvent>();
  

Generic events interface

To use with generic events interface:

interface MyClassEvents<T> {
  'added': (el: T, wasNew: boolean) => void;
}

class MyClass<T> extends TypedEmitter<MyClassEvents<T>> {

}

Compatible subclasses with different events

The type of eventNames() is a superset of the actual event names to make subclasses of a TypedEmitter that introduce different events type compatible. For example the following is possible:

class Animal<E extends ListenerSignature<E>=ListenerSignature<unknown>> extends TypedEmitter<{spawn: () => void} & E> {
  constructor() {
    super();
  }
}

class Frog<E extends ListenerSignature<E>> extends Animal<{jump: () => void} & E> {
}

class Bird<E extends ListenerSignature<E>> extends Animal<{fly: () => void} & E> {
}

const animals: Animal[] = [new Frog(), new Bird()];

No Overhead

Library adds no overhead. All it does is it simply reexports renamed EventEmitter with customized typings. You can check lib/index.js to see the exported code.