typed-event-emitter-2

This module provides a strict usage and implementation of Node.js' EventEmitter API. Without needing to rely on another implementation. Arbitrary events or listeners can not be added without a TypeScript compile time error.

Install

$ npm i typed-event-emitter-2

Usage

Before using Node.js / Browsers conventional EventEmitter.

import * as UntypedEventEmitter from 'events';
 
const conventionalEventEmitter = new UntypedEventEmitter();
 
conventionalEventEmitter
    .on('foo', (arg: number) => console.log(Math.abs(arg)))
    .on('bar', (arg: string) => console.log(arg.length))
    .on('baz', () => console.log('baz'));
 
conventionalEventEmitter.emit('foo', 1);
conventionalEventEmitter.emit('foo'); // Should have an error
conventionalEventEmitter.emit('bar', 'bar');
conventionalEventEmitter.emit('bar', 1); // Should have an error
conventionalEventEmitter.emit('baz');
conventionalEventEmitter.emit('baz', 'bar'); // Should have an error

Using a type safe EventEmitter with no arguments in listeners.

import TypedEventEmitter from 'typed-event-emitter-2';
 
const typedEventEmitterNoArgs = new TypedEventEmitter<'foo' | 'baz'>();
 
typedEventEmitterNoArgs
    .on('foo', () => console.log('foo'))
    .on('baz', () => console.log('baz'));
 
typedEventEmitterNoArgs.emit('baz');
typedEventEmitterNoArgs.emit('foo');

Using a type safe EventEmitter with one argument in listeners.

import TypedEventEmitter from 'typed-event-emitter-2';
 
class TypedEventEmitterOneArg extends TypedEventEmitter<never, {
    foo: number
    bar: string
}> {}
 
const typedEventEmitterOneArg = new TypedEventEmitterOneArg();
typedEventEmitterOneArg
    .on('foo', (arg: number) => console.log(Math.abs(arg)))
    .on('bar', (arg: string) => console.log(arg.length));
 
typedEventEmitterOneArg.emit('foo', 1);
typedEventEmitterOneArg.emit('bar', 'bar');

Using a type safe EventEmitter with zero or one arguments in listeners.

import TypedEventEmitter from 'typed-event-emitter-2';
 
enum keys {
    baz,
    zoo,
};
 
const typedEventEmitterMix = new TypedEventEmitter<
    keyof typeof keys,
    {
    	foo: number
    	bar: string
    }
>();
 
typedEventEmitterMix
    .on('foo', (arg: number) => console.log(Math.abs(arg)))
    .on('bar', (arg: string) => console.log(arg.length))
    .on('baz', () => console.log('baz'));
 
typedEventEmitterMix.emit('foo', 1);
typedEventEmitterMix.emit('bar', 'bar');
typedEventEmitterMix.emit('zoo');

License

typed-event-emitter-2 is licensed under the ISC License.