Javascript Web Application: PusSub Object

PusSub.js

var PubSub = {
		subscribe: function(ev, callback) {
		// Create _callbacks object, unless it already exists 
		var calls = this._callbacks || (this._callbacks = {});
		// Create an array for the given event key, unless it exists, then 
		// append the callback to the array
		(this._callbacks[ev] || (this._callbacks[ev] = [])).push(callback);
		return this; 
	},
	publish: function() {
		// Turn arguments object into a real array
		var args = Array.prototype.slice.call(arguments, 0);
		// Extract the first argument, the event name 
		var ev = args.shift();
		// Return if there isn't a _callbacks object, or
		// if it doesn't contain an array for the given event
		var list, calls, i, l;
		if (!(calls = this._callbacks)) return this;
		if (!(list = this._callbacks[ev])) return this;
		// Invoke the callbacks
		for (i = 0, l = list.length; i < l; i++)
			list[i].apply(this, args);
		
		return this;
	} 
};

To Test it:

PubSub.subscribe("wem", function () {
console.log("web!");
});
PubSub.publish("wem");