Abstract class to add Event Emitter functionality for decoupling objects, setting up patterns (PubSub, Mediator, Observer)

EventEmiterBehaviour.js

/**
* Provides Event Emitter functionality
* 
* Allows decoupling existing classes/prototypes
* Events are emitted in Sync.
* 
* Usage
* @example
*
*	function YourClass()
*	{
*		EventEmitterBehaviour.constructor.call(this)
*	}
*
* 	YourClass.prototype = new EventEmitterBehaviour()
* 
* @module EventEmitterBehaviour
*/
var EventEmitterBehaviour = (function () {

/**
* @class EventEmitterBehaviour
* @constructor
*/
function EventEmitterBehaviour()
{
	Object.defineProperty(this, '_events', {
		configurable: false,
		enumerable: false,
		value: {}
	})
}

/**
* Emits an event
*
* @method emit
* @param evt {String}
* @param ... {Mixed}
*/
EventEmitterBehaviour.prototype.emit = function(evt) 
{
	if (this._events[evt] && this._events[evt].length)
	{
		var args = Array.prototype.slice.call(arguments, 1)
		var count = this._events[evt].length
		for (var i = 0; i <count; i++) {
			this._events[evt][i].apply(this, args)
		}
	}
	return this
}

/**
* Subscribe to a event
*
* @method on
* @param evt {String}
* @param callback {Function}
*/
EventEmitterBehaviour.prototype.on = function(evt, callback) 
{
	if (Object.prototype.toString.call(this._events[evt]) === '[object Array]')
	{
		this._events[evt].push(callback)
	}
	else
	{
		this._events[evt] = [callback]
	}
	return this
}

/**
* Unsubscribes from a event
*
* @method off
* @param evt {String}
* @param [callback] {Function}
*/
EventEmitterBehaviour.prototype.off = function(evt, callback) 
{
	if (this._events[evt] && this._events[evt].length)
	{
		if (typeof callback === 'function')
		{
			this._events[evt].splice(this._events[evt].indexOf(callback), 1)
		}
		else
		{
			this._events[evt] = []
		}
	}
	return this
}

// expose
return EventEmitterBehaviour
})();