nanoevents

What is nanoevents?

Nanoevents is a tiny (less than 1KB) event emitter library for JavaScript. It provides a simple and efficient way to handle events in your application, making it ideal for both client-side and server-side development.

What are nanoevents's main functionalities?

Event Emission

This feature allows you to emit events with associated data. The `emit` method triggers all listeners attached to the specified event.

const { createNanoEvents } = require('nanoevents');
const emitter = createNanoEvents();
emitter.emit('event', 'data');

Event Listening

This feature allows you to listen for specific events. The `on` method registers a callback function that will be called whenever the specified event is emitted.

const { createNanoEvents } = require('nanoevents');
const emitter = createNanoEvents();
emitter.on('event', data => {
  console.log(data);
});
emitter.emit('event', 'data');

Event Unsubscription

This feature allows you to unsubscribe from events. The `on` method returns an unsubscribe function that can be called to remove the listener.

const { createNanoEvents } = require('nanoevents');
const emitter = createNanoEvents();
const unsubscribe = emitter.on('event', data => {
  console.log(data);
});
emitter.emit('event', 'data');
unsubscribe();
emitter.emit('event', 'data');

Other packages similar to nanoevents

eventemitter3

EventEmitter3 is a high-performance event emitter for Node.js and the browser. It is more feature-rich compared to Nanoevents, offering wildcard event listeners and more advanced event handling capabilities.

mitt

Mitt is another tiny event emitter library. It is similar in size and simplicity to Nanoevents but offers a slightly different API. Mitt is also less than 1KB and is designed for minimal overhead.

events

The 'events' package is the Node.js core EventEmitter module extracted for use in browser environments. It is more heavyweight compared to Nanoevents but offers a robust set of features and is widely used in the Node.js ecosystem.

README

Nano Events

Simple and tiny event emitter library for JavaScript.

• No Node.js EventEmitter compatibility.
• Only 115 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()
}

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.emitter, 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) //=> { }

Changelog

1.0.7

• Reduce size (by Vladlen Grachev).