eventemitter3

What is eventemitter3?

The eventemitter3 package is a high-performance event emitter library that provides an interface for emitting and listening to events. It is a drop-in replacement for existing EventEmitter implementations with a focus on performance.

What are eventemitter3's main functionalities?

Emitting events

This feature allows you to emit events with a specified name and pass arguments to the event listeners.

const EventEmitter = require('eventemitter3');
const emitter = new EventEmitter();
emitter.on('greet', function(message) {
  console.log(message);
});
emitter.emit('greet', 'Hello World!');

Listening to events

This feature allows you to add a listener for a specific type of event. The listener will be invoked when an event with that name is emitted.

const EventEmitter = require('eventemitter3');
const emitter = new EventEmitter();
emitter.on('greet', function(message) {
  console.log(message);
});

Removing event listeners

This feature allows you to remove a specific listener from an event so that it no longer gets called when the event is emitted.

const EventEmitter = require('eventemitter3');
const emitter = new EventEmitter();
function onGreet(message) {
  console.log(message);
}
emitter.on('greet', onGreet);
emitter.removeListener('greet', onGreet);

Once listeners

This feature allows you to add a one-time listener for an event. The listener will be invoked only the first time the event is emitted, after which it is removed.

const EventEmitter = require('eventemitter3');
const emitter = new EventEmitter();
emitter.once('greet', function(message) {
  console.log('This will only be logged once:', message);
});
emitter.emit('greet', 'Hello World!');
emitter.emit('greet', 'Hello again!');

Other packages similar to eventemitter3

events

The 'events' package is Node.js's native event emitter implementation. It is very similar to eventemitter3 but may not be as optimized for performance.

mitt

Mitt is a tiny functional event emitter / pubsub. It offers the same core functionality as eventemitter3 but with a smaller footprint and a functional API.

wolfy87-eventemitter

Wolfy87's EventEmitter is an implementation of the EventEmitter module found in Node.js but can be used in the browser. It is larger in size compared to eventemitter3 and includes additional features like namespaces and wildcard listeners.

README

EventEmitter3

EventEmitter3 is a faster alternative to EventEmitter2 and the built-in EventEmitter that ships within Node.js. It removes some features that you might not need:

• Domain support.
• Thrown errors when there are no error listeners specified.
• That a newListener event is emitted when an event is emitted.
• No silly setMaxListeners.
• No silly listenerCount function.. Just do EventEmitter.listeners(event).length

And adds some features you want:

• Emit events with a custom context without binding: EE.on(event, fn, context) which also works with once EE.once(event, fn, context)

It's a drop in replacement of your existing EventEmitters, but just faster. Free performance, who wouldn't want that?

The source of the EventEmitter is compatible for browser usage, no fancy pancy Array.isArray stuff is used, it's just plain ol JavaScript that should even work IE5 if you want to. This module currently serves its use in Primus's client file.

Installation

$ npm install --save eventemitter3

or as a component

$ component install eventemitter3

then

var EventEmitter = require('eventemitter3');

// or

var EventEmitter = require('eventemitter3').EventEmitter;

For API methods see the official Node.js documentation:

http://nodejs.org/api/events.html