Nano Events
Simple and tiny event emitter library for JavaScript.
- Only 107 bytes (minified and brotlied). It uses Size Limit to control size.
- The
onmethod returnsunbindfunction. You don’t need to save callback to variable forremoveListener. - TypeScript and ES modules support.
- No aliases, just
emitandonmethods. No Node.js EventEmitter compatibility.
import { createNanoEvents } from 'nanoevents'
const emitter = createNanoEvents()
const unbind = emitter.on('tick', volume => {
summary += volume
})
emitter.emit('tick', 2)
summary //=> 2
unbind()
emitter.emit('tick', 2)
summary //=> 2
Table of Contents
- Install
- TypeScript
- Mixing to Object
- Add Listener
- Remove Listener
- Execute Listeners
- Events List
- Once
- Remove All Listeners
Install
npm install nanoeventsTypeScript
Nano Events accepts interface with event name to listener argument types mapping.
interface Events {
set: (name: string, count: number) => void,
tick: () => void
}
const emitter = createNanoEvents<Events>()
// Correct calls:
emitter.emit('set', 'prop', 1)
emitter.emit('tick')
// Compilation errors:
emitter.emit('set', 'prop', '1')
emitter.emit('tick', 2)Mixing to Object
Because Nano Events API has only just 2 methods, you could just create proxy methods in your class or encapsulate them entirely.
class Ticker {
constructor () {
this.emitter = createNanoEvents()
this.internal = setInterval(() => {
this.emitter.emit('tick')
}, 100)
}
stop () {
clearInterval(this.internal)
this.emitter.emit('stop')
}
on (event, callback) {
return this.emitter.on(event, callback)
}
}With Typescript:
import { createNanoEvents, Emitter } from "nanoevents"
interface Events {
start: (startedAt: number) => void
}
class Ticker {
emitter: Emitter
constructor () {
this.emitter = createNanoEvents<Events>()
}
on<E extends keyof Events>(event: E, callback: Events[E]) {
return this.emitter.on(event, callback)
}
}Add Listener
Use on method to add listener for specific event:
emitter.on('tick', number => {
console.log(number)
})
emitter.emit('tick', 1)
// Prints 1
emitter.emit('tick', 5)
// Prints 5In case of your listener relies on some particular context
(if it uses this within itself) you have to bind required
context explicitly before passing function in as a callback.
var app = {
userId: 1,
getListener () {
return () => {
console.log(this.userId)
}
}
}
emitter.on('print', app.getListener())Note: binding with use of the .bind() method won’t work as you might expect
and therefore is not recommended.
Remove Listener
Methods on returns unbind function. Call it and this listener
will be removed from event.
const unbind = emitter.on('tick', number => {
console.log('on ' + number)
})
emitter.emit('tick', 1)
// Prints "on 1"
unbind()
emitter.emit('tick', 2)
// Prints nothingExecute Listeners
Method emit will execute all listeners. First argument is event name, others
will be passed to listeners.
emitter.on('tick', (a, b) => {
console.log(a, b)
})
emitter.emit('tick', 1, 'one')
// Prints 1, 'one'Events List
You can get used events list by events property.
const unbind = emitter.on('tick', () => { })
emitter.events //=> { tick: [ [Function] ] }Once
If you need add event listener only for first event dispatch, you can use this snippet:
class Ticker {
constructor () {
this.emitter = createNanoEvents()
}
…
once (event, callback) {
const unbind = this.emitter.on(event, (...args) => {
unbind()
callback(...args)
})
return unbind
}
}Remove All Listeners
emitter.on('event1', () => { })
emitter.on('event2', () => { })
emitter.events = { }