An enhanced EventEmitter with extra methods for detecting whether an event has any handlers or not for efficient event handler attachment.

Install

npm install emitter-b

or download the built package EmitterB.umd.js from the 'dist' folder in the repository

Usage

var EmitterB = require('emitter-b')  // node.js and webpack

define(['EmitterB.umd.js'], function(EmitterB) { ... } // amd

<script src="EmitterB.umd.js">&lt;/script>
<script>
  EmitterB; // global 'EmitterB' module object
</script>

All methods and properties from EventEmitter are inherited. Most of these are inherited from EventEmitter. The important ones:

emitter.emit(event, data, data2, ...) - Emits an event that triggers handlers setup via the Gem's on methods.

emitter.on(event, callback) - Registers a callback that will be called when the passed event is emitted.

• event - The string event name to listen for.
• callback(data, data2, ...) - the callback gets any arguments passed to emit after the event name.

emitter.once(event, callback) - Like on but the callback will only be called the first time the event happens.

emitter.off(event, callback) - Removes a callback as an event handler (the callback won't be called for that event again). emitter.removeListener(event,callback) - Same as off.

emitter.removeAllListeners(event) - Removes all the callbacks for the passed event. emitter.removeAllListeners() - Removes all callbacks.

ifon

The ifon and related methods are useful primarily for performance reasons. They allow registering event listeners only when they're needed, so that the browser doesn't get overloaded with event handlers. Its recommended that ifon is used whenever possible.

An example:

var child = EmitterB()
var parent = EmitterB()

var handler;
parent.ifon('someoneClickedTheThing', function() {
    child.on('click', handler = function() {
        parent.emit('someoneClickedTheThing', "I can't believe it")
    })
})
parent.ifoff('someoneClickedTheThing', function() {
    child.off('click', handler)
})

emitter.ifon(event, callback) - Registers a callback that will be called when a handler is registered for event if it had no handler registered previously. If there is already a listener attached to that event, callback is called immediately.
emitter.ifon(callback) - Registers a callback that will be called when the first handler for any event is registered.

• callback(event) - The callback gets the newly registered event type as its argument.

emitter.ifoff(event, callback) - Registers a callback that will be called when the last handler for event is unregistered.
emitter.ifoff(callback) - Registers a callback that will be called when the last handler for any event is unregistered.

• callback(event) - The callback gets the unregistered event type as its argument.

emitter.removeIfon() - Removes all ifon handlers.
emitter.removeIfon(event) - Removes all ifon handlers for the passed event.
emitter.removeIfon(callback) - Removes callback as an "all" ifon handler (a callback passed to ifon without an event).
emitter.removeIfon(event, callback) - Removes callback as an ifon handler for the passed event.

emitter.removeIfoff() - Removes all ifoff handlers.
emitter.removeIfoff(event) - Removes all ifoff handlers for the passed event.
emitter.removeIfoff(callback) - Removes callback as an "all" ifoff handler (a callback passed to ifoff without an event).
emitter.removeIfoff(event, callback) - Removes callback as an ifoff handler for the passed event.

proxy

The proxy method uses ifon and ifoff to minmize the number of event listeners that need to be attached in the system.

emitter.proxy(emitter, options) - Proxies event registration to emitter.

• emitter - The emitter (usually a Gem) to proxy handler binding to
• options - An object that defines what events are proxied. If undefined, all events are proxied. The object can have one of the following properties:
  • only - An array of events to proxy.
  • except - An array of events to not proxy. All other events are proxied.

Example of proxy:

var A = Text()
var B = Text()

A.proxy(B)
A.on("click", function(arg) {
    console.log("hey hey heyyy! "+arg)
})

B.emit("click", "Ughh..") // console prints "hey hey heyyy! Ughh.."

Todo

Changelog

• 1.0.0 - Initial commit - code transferred from Gem.js.

How to Contribute!

Want to contribute? Start with the Contributing Guide!

Anything helps:

• Creating issues (aka tickets/bugs/etc). Please feel free to use issues to report bugs, request features, and discuss changes.
• Updating the documentation: ie this readme file. Be bold! Help create great documentation!
• Submitting pull requests.

License

Released under the MIT license: http://opensource.org/licenses/MIT