Library agnostic invokation events for functions

couple.js

(function () {
	"use strict";
	/**
	 * Add event couplings to a function, enabling aspect-oriented design patterns
	 *
	 * @return	Function 	Coupled function
	 **/
	Function.prototype.couple = function () {
		var fn = this,
			events = {before: {}, after: {}};
			wFn = function () {
				var i, 
					token = {
						context: this,
						args: Array.prototype.slice.apply(arguments),
						returned: null,
						event: 'before'
					};
				if (false === triggerEvents(token)) 
					return null;
				
				token.returned = fn.apply(token.context, token.args);
				token.event = after;
				if (false === triggerEvents(token))
					return null;
				
				return token.returned;
			};
		function triggerEvents(token) {
			for (var i in events[token.event]) {
				if (false === events[token.event][i].call(token.context, token))
					return false;
			}
			return true;
		}
		function addEventMethod(which) {
			return function () {
				for (var i=0; i<arguments.length; i++) 
					events[which][arguments[i]] = arguments[i];
				return wFn;
			};
		}
		/**
		 * Insert a closure before the invokation of the coupled function
		 * 
		 * @rest	Function[context](token)	closure to insert
		 * 	@param	Object	token			Invokation token
		 *	@param	Object	token.context	Context in which the function was called
		 * 	@param	Array 	token.args		Arguments with which the function was called
		 * 	@param	Object	token.returned	Return value of the function (null for before)
		 * 	@param	String	token.event		Event on which the handler was called
		 * 	@return	Boolean	Whether to continue event handling.  For before, determines whether invokation completes.
		 * @return Function	Coupled function (chainable)
		 **/
		wFn.before = addEventMethod('before');
		/**
		 * Insert a closure after the invokation of the coupled function
		 * @see	wFn.before
		 **/
		wFn.after = addEventMethod('after');
		/**
		 * Remove an event handler
		 **/
		wFn.decouple = function () {
			for (var i=0; i<arguments.length; i++) {
				delete events.before[arguments[i]];
				delete events.after[arguments[i]];
			}
			return wFn;
		};
		/**
		 * The original function
		 **/
		wFn.original = fn;
		
		return wFn;
	};
}());