Observable.js

/*global define*/
/**
 * Simple Observable Patter
 */
define(function(){
	
	function Observable(){}

	Observable.prototype = {
		/**
		 * Initializes the events
		 */
		_initEvents: function(){
			if( this._events ) return
			this._events = {
				all: []
			}

		},

		/**
		 * Adds an observer
		 * @param  {String}   	evt      	event name
		 * @param  {Function} 	callback 	calback function
		 * @param  {Object}		context		the referenced this
		 * @return {Observable} this
		 */
		on: function(evt, callback, context){
			evt = evt || 'all'

			this._initEvents()
			
			if(!this._events[ evt ])
				this._events[ evt ] = []

			this._events[ evt ].push({ 
					cb: callback, 
					ctx: context 
				})

			return this
		},

		/**
		 * Removes an observer (callback) from
		 * the specified event list
		 * @param  {String}   	evt      	event name
		 * @param  {Function} 	callback 	calback function
		 * @param  {Object}		context		the referenced this
		 * @return {Observable} this
		 */
		off: function(evt, callback, context){
			var callbacks, i, tuple

			evt = evt || 'all'

			this._initEvents()

			callbacks = this._events[evt]

			if( !callbacks ) return this

			for( i = callbacks.length; i--; ){
				tuple = callbacks[i]
				if( tuple.cb == callback && tuple.ctx == context ){
					callbacks.splice( i, 1 )
					return this
				}
			}

			return this
		},

		/**
		 * Fires the event. Callable with any numer of arguments,
		 * but first the event name
		 * @param  {String} evt the event name
		 */
		trigger: function( evt ){
			this._initEvents()
			

			var callbacks = this._events[ evt ],
				i, tuple

			if( callbacks ) for( i = callbacks.length; i--; ){
				try{
					tuple = callbacks[i]
					tuple.cb.apply( tuple.ctx, arguments )
				}catch(e){
					console.error( 'Error executing callback: ' +
						'(' + tuple.cb.name + ')' + 
						e.message )
				}
			}
			
			// Those subscribed to all events shall be notified
			// allways
			if( evt != 'all' ){
				callbacks = this._events[ 'all' ]

				for( i = callbacks.length; i--; ){
					try{
						tuple = callbacks[i]
						tuple.cb.apply( tuple.ctx, arguments )
					}catch(e){
						console.error( 'Error executing callback: ' +
							'(' + tuple.cb.name + ')' + 
						e.message )	
					}
				}
			}	
			return this
		}
	}

	return Observable
})