necolas / emitter.js

A simple JavaScript event-emitter

emitter.js

JavaScript event-emitter.

Installation

npm: npm install emitter.js Component(1): component install necolas/emitter.js Bower: bower install emitter.js

API

Emitter(obj)

The Emitter function can be used as a Constructor or as a mixin.

As an Emitter instance:

var Emitter = require('emitter');
var foo = new Emitter;
foo.trigger('foo');

As a mixin:

var Emitter = require('emitter');
var foo = {};
Emitter(foo);

foo.trigger('bar');

As a prototype mixin:

var Emitter = require('emitter');
var Foo = function () {};
Emitter(Foo.prototype);

Emitter#on(event, callback)

Register an event handler callback. Protects against duplicate handlers being registered.

var handler = function () {
  console.log('The function `handler` has been registered for the event `foo`.');
};

foo.on('foo', handler);

Emitter#once(event, callback)

Register a one-off event handler callback, removed immediately after it is invoked the first time.

var handler = function () {
  console.log('The function `handler` has been registered as a one-off callback for the event `foo`.');
};

foo.once('foo', handler);

Emitter#off([event], [callback])

Remove the event handler callback. If no callback is specified, it will remove all callbacks for the event. If no event is specified, the entire event registry will be deleted.

var handler = function () {
  console.log('Registered for the event `foo`.');
};

foo.off('foo', handler);
foo.off('foo');
foo.off();

Emitter#trigger(event, [...])

Trigger an event with optional arguments. Alias: emit.

var data = { name: 'nicolas' };
foo.trigger('foo', data);

Emitter#getListeners(event)

Return an array of callbacks registered for the event, or an empty array. Initializes the registry if necessary.

foo.getListeners('foo');

Emitter#hasListeners(event)

Check if any callbacks are registered for the event.

foo.hasListeners('foo');

Testing

Install and run the test suite:

make

Re-run the test suite:

make test

Browser support

• Google Chrome (latest)
• Opera (latest)
• Firefox 4+
• Safari 5+
• Internet Explorer 8+

emitter.js's Issues

Why throw an error if an event is not registered?

https://github.com/necolas/emitter.js/blob/master/emitter.js#L223
I don't understand why you throw an error here. It should be ignored. The common use case for events is that an object triggers events and you can choose to listen to them. You're not required.

off(): Remove `_wrapper` from callback

Should probably clean up and not leave the wrapped function attached to the callback once it's been removed.

support automatic re-emit event?

let me explain the idea by taking an example:

says i have a event which called 'ready', it fires when my object is ready.

After the event is fired, that means my object will stay "ready" forever,
so i also would like to make sure, later if any callback gets added to 'ready' event, it gets called directly with the arguments previously emitted.

obj.reemit('ready',1,2,3);
obj.on('ready', function callback(){ console.log(arguments);});
// output "[1, 2, 3]"

wouldn't it be cool?