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

Let's say you have a state manager object to control the state of your app.

function StateManager() {}
StateManager.prototype.updateState = function updateState(payload) {
  // update state
  // ...
  // and inform listeners that the state has just updated
  this.emit('update')
}
module.exports = StateManager

To plug event emitter into your state manager:

StateManager.prototype = Object.assign({}, StateManager.prototype, EventEmitter.prototype)

Now, you can listen and emit events within your state manager:

const state = new StateManager()
state.on('update', function() {
  console.log('State updated!')
})

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')

.flush()

Removes all events and listeners.

emitter.flush()

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