best-events

Tiny type-safe event machine

Why

Lets you strictly type your events and only fire and listen for events with specified names and sets of arguments

Installation

npm i best-events

Usage

Import

import Events from 'best-events'

Provide type annotations

Event types should be provided as a generic when instantiating the class.

The generic type should provide a map of all possible events, where key is the event's name and value is its callback:

const events = new Events<{
  hello: (name: string) => void
  math: (a: number, b: number) => void
}>()

It's also possible to use tuple types for callbacks, which is less verbose:

const events = new Events<{
  hello: [name: string] // provide argument names for intellisense
  math: [number, number] // or keep them anonymous
}>()

Fire and Listen the events

With enabled type safety:

// ✅ OK
events.on('hello', (name) => console.log('hello ' + name))
events.fire('hello', 'world')

// ✅ OK
events.on('math', (a, b) => console.log(a + b))
events.fire('math', 1, 2)

// ❌ WRONG ARGUMENT TYPE
// Argument of type 'number' is not assignable to parameter of type 'string'
events.fire('hello', 1)

// ❌ NOT ENOUGH ARGUMENTS
// Expected 3 arguments, but got 2
events.fire('math', 1)

// ❌ TOO MANY ARGUMENTS
// Argument of type '(name: any, lastName: any) => void' is not assignable to parameter of type '(name: string) => void'
events.on('hello', (name, lastName) => console.log('hello ' + name + lastName))

// ❌ UNKNOWN EVENT
// Argument of type '"howdy"' is not assignable to parameter of type '"hello" | "math"'
events.fire('howdy', 'world')

// ❌ WRONG TYPE IN LISTENER
// Property 'push' does not exist on type 'number'
events.on('math', (a, b) => a.push(b))

Methods

on to listen to the event

const myEventHandler = (value: string) => console.log(value)
events.on('myEvent', myEventHandler)

on returns an "off" function, which can be used as an alternative to the off method:

const offMyEvent = events.on('myEvent', (value) => console.log(value))
offMyEvent()

fire to emit the event

events.fire('myEvent', 'Some value')

off to remove a specific listener

events.off('myEvent', myEventHandler)

offAll to remove all listeners

(Use this one with caution, you might remove the event listener that was assigned elsewhere)

events.offAll('myEvent')

Usage without TS

Also supported but discouraged

import Events from 'best-events'

const events = new Events()

events.on('hello', (name) => console.log('hello ' + name))

events.fire('hello', 'world')