Javascript Event Emitter Object

A simple event emitter object that you can plug into your javascript libraries.

API is very similar to the node.js events.

Install

npm install event-emitter-object

Import

This package exports multiple builds. Developer has the responsibility to choose the one that best fits to her/his needs.

1. Minified (default)

This is basically the source code itself but minified. There are no compilation and polyfills inside. Use it if you already have a compiler (like babel) and polyfills in your project. (which is mostly is the case.)

const EventEmitter = require('event-emitter-object')

2. UMD Bundle

The source code bundled with browserify to generate a UMD bundle. This bundle can also be imported by html script tag. No compilation and polyfills. The variable attached to the browser's window object is EventEmitterObject.

const EventEmitterObject = require('event-emitter-object/dist/umd')

or

<script src="https://unpkg.com/event-emitter-object@1/dist/umd.js" crossorigin type="text/javascript"></script>

3. Polyfilled UMD bundle

The source code compiled with babel and bundled with browserify to generate a UMD bundle. This bundle can also be imported by html script tag. The variable attached to the browser's window object is EventEmitterObject.

<script src="https://unpkg.com/event-emitter-object@1/dist/umd.polyfilled.js" crossorigin type="text/javascript"></script>

Use

This is a pure javascript object which can be used as a super class of another objects or as a standalone.

Using it as a standalone library

const EventEmitter = require('event-emitter-object')

const logger = new EventEmitter()

logger.on('criticalError', function(err) {
  // send log to the server
})

if (resourceNotFound) {
  logger.emit('criticalError', [new Error('resourceNotFound')])
}

Using as a super class

const EventEmitter = require('event-emitter-object')

// A Logger object which inherits the methods of EventEmitter
const initialEvents = {} // you may not send this
function Logger() {
  EventEmitter.call(this, initialEvents)
}
Logger.prototype = Object.create(EventEmitter.prototype)
Logger.prototype.constructor = Logger

Logger.prototype.propertyYouWant = function() {}

// Initiate a logger for a particular type of logs
const errorLogger = new Logger()
errorLogger.on('error', function(err) {
  // send log to the server
})
if (resourceNotFound) {
  errorLogger.emit('error', [new Error('resourceNotFound')])
}

API

.on(eventName, callback, opts)

Registers a new listener for a certain event.

emitter.on('someEvent', function() {
  console.log('Some event happened in some emitter.')
}, {
  once: true // default is false
})

.once(eventName, callback)

This is a shortcut for the on method with {once: true}:

// instead of doin this:
emitter.on('someEvent', function(){}, {once: true})
// you can do this:
emitter.once('someEvent', function(){})

.emit(eventName, args)

Emits a certain event with arguments.

emitter.emit('someEvent')

// or with arguments
emitter.on('anotherEvent', function(arg1, arg2) {
  console.log('Another event emitted with arguments: ', arg1, arg2)
})
emitter.emit('anotherEvent', ['hello', 'world'])

.removeListeners(eventName)

Removes all listeners that belong to a certain event.

emitter.removeListeners('someEvent')

.flushEventEmitter()

Removes all events and listeners.

emitter.flushEventEmitter()

Babel Polyfills Report

This module uses the following polyfills in its polyfilled builds.

1. es.array.splice
2. es.date.to-string
3. es.object.to-string
4. es.regexp.to-string
5. es.array.reduce
6. es.object.keys