Simple and tiny (117 bytes) event emitter library for JavaScript
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Latest commit e32e47f Jul 17, 2018

README.md

Nano Events

Simple and tiny event emitter library for JavaScript.

  • No Node.js EventEmitter compatibility.
  • Only 117 bytes (minified and gzipped). It uses Size Limit to control size.
  • on method returns unbind function. You don’t need to save callback to variable for removeListener.
  • No aliases, just emit and on methods.
import NanoEvents from 'nanoevents'
const emitter = new NanoEvents()

const unbind = emitter.on('tick', volume => {
  summary += volume
})

function disable () {
  unbind()
}
Sponsored by Evil Martians

Usage

Mixing to Object

Because main Nano Events API has only 2 methods, you could just create proxy methods in your class:

class Ticker {
  constructor() {
    this.emitter = new NanoEvents()
  }
  on() {
    return this.emitter.on.apply(this.events, arguments)
  }
  tick() {
    this.emitter.emit('tick')
  }
}

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', 2)
// Prints "2"

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 nothing

Execute 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', () => { })
Object.keys(emitter.events) //=> ["tick"]

unbind()
Object.keys(emitter.events) //=> []

Helpers

Once

If you need add event listener only for first event dispatch, you can use this snippet:

class Ticker {
  constructor() {
    this.emitter = new NanoEvents()
  }
  …
  once (event, callback) {
    const unbind = this.emitter.on(event, function () {
      unbind()
      callback.apply(this, arguments)
    })
    return unbind
  }
}

Remove all listeners

unbindAll method will remove all listeners to all events.

import unbindAll from 'nanoevents/unbind-all';

emitter.on('event1', () => { })
emitter.on('event2', () => { })

unbindAll(emitter);

Object.keys(emitter.events) //=> { }