gistfile1.js

/**********************************************************************************
* 
* @author Jordan Boesch
* @version 1.2
* @link http://boedesign.com/blog/2010/02/13/hijacking-javascriptjquery-methods/
* @date Feb 20, 2010
*
* Hijack is a little snippet of code that allows you to hijack arguments passed to
* functions/methods.  Not only can you alter arguments, but you call the old method
* from within the hijacked function (2nd param) and 'return false' if you want to call the
* function yourself.
*
* Be aware that this was more-so a proof of concept.  I don't
* fully recommend hijacking and overwriting methods but it does have its uses. 
* I thought I would attempt it by making it easy to do... It's still "eval" ;)
* 
* USAGE:
* 
* Here is how you could hijack the css method in jQuery:
*
----------------------------------------------------------------------------------
var hijackedjQueryCSS = new Hijack('jQuery.fn.css', function(user_args, old_method){
		
	var args = user_args;
	
	if(args[1] == 'dark-violet'){
		args[1] = '#6B238E';
	}
	
	return args;
	
});
----------------------------------------------------------------------------------
*
* Now if you run this:
*
----------------------------------------------------------------------------------
$('body').css('color', 'dark-violet')
----------------------------------------------------------------------------------
*
* it will change the color to the hex value you set in your hijacked method.
*
* You can also restore the original method by calling destroy() like so:
*
*
----------------------------------------------------------------------------------
hijackedjQueryCSS.destroy();
----------------------------------------------------------------------------------
*
* Now when you run the code that sets the color to dark-violet, nothing will happen.
*
* If you're interested in over-writing the MooTools css method, then you would use
* this string: Element.prototype.setStyle as the first parameter.
*/

/**
* Allows you to alter with arguments before the method is actually called
* @param {Function} method A method/function to call after doing some tampering
* @param {Function} cb A callback that is passed the arguments for you to play with
* @constructor
*/

function Hijack(method_name, cb){
	
	// A function needs to be passed or there will be hell to pay
	if(Object.prototype.toString.call(cb) !== "[object Function]"){
		throw new Error('An anonymous function must be passed as the second parameter!');
	}
	
	var self = this,
		method_old = eval(method_name); // Keep track of the old one to call 
	
	// Make sure this is the first time we create an instance for this method
	if(!Hijack._inArray(method_name, Hijack._methodInstances)){
		
		// Store it, just in case we need to restore it for "destroy"
		self._orig = { method_name: method_name, method_old: method_old };
		Hijack._methodInstances.push(method_name);
		
		// Evil, I know.. 
		eval(method_name + " = function(){var args = Array.prototype.slice.call(arguments);if(a = cb.call(this, args, method_old)){return method_old.apply(this, a)}};");
		
	}
	// F off.
	else {
		throw new Error('You cannot create multiple instances of a specific method (yet), sorry!');
	}
	
}

Hijack.prototype = {
	
	/**
	* Bring it back to the original method (before it was hijacked)
	* @public
	*/
	destroy: function(){
	
		var self = this;
		eval(self._orig.method_name + " = function(){ return self._orig.method_old.apply(this, arguments); }");
	
	}
	
}

/**
* Keep track of methods being hijacked, you can only hijack a method once!
* @private (but not really)
*/
Hijack._methodInstances = [];

/**
* Searches an array for a specific value
* @param {String} needle What you're searching for
* @param {Array} haystack What you're searching in
* @private (but not really)
*/
Hijack._inArray = function(needle, haystack){
	
	for(var i = 0, length = haystack.length; i < length; i++) {
	    if(haystack[i] == needle) return true;
	}
	
	return false;
	
}