simplyfied requestAnimationFrame

gistfile1.js

/**
 * An even more common approach to look for vendor specific implementations in
 * the browsers javascript object model.
 * lookUpImplementation(vendors,subject,functionName,replacement) is reusable
 * for other tasks too :-)
 */
var vendors = ['webkit','moz','o','ms'];
window.requestAnimationFrame = lookUpImplementation(
	vendors, window, 'requestAnimationFrame'
	,function(step) {
		return setInterval(step, 1000/60);
	}
);
window.cancelAnimationFrame = lookUpImplementation(
	vendors, window, 'cancelAnimationFrame'
	,function(id) {
		clearInterval(id);
	}
);

/** PrivateFunction: lookUpImplementation(vendors, subject, functionName, replacement)
 * Searches for a function with the name "functionName" inside of
 * "subject".
 * If the function was not found, the vendor prefixes from the array
 * "vendors" are prepended to "functionName" to check, if a function
 * from the regarding vendor exists.
 * If a "native" or a "vendor" implementation was found, it gets
 * returned. If not, "replacement" gets returned instead (if given)
 *
 * "functionName" will be reformatted automatically to match
 * camelcase notation when prepending vendor prefixes. Means:
 * "toLookup" becomes automatically "webkitToLookup".
 *
 * Parameters:
 *     (Array) vendors - vendor prefixes like "webkit" or "moz"
 *     (mixed) subject - an object too search for implementations
 *     (String) functionName - name of the implementation
 *     (Function) replacement - this gets returned if a native nor a 
 *                              vendor specific implementation was found.
 *
 * Returns:
 *     (Function|undefined)
 */
function lookUpImplementation(vendors, subject, functionName, replacement) {
	var implementation;
	
	if(subject) {
		if(subject[functionName]) {
			implementation = subject[functionName];
		} else {
			var camelnotation = functionName.substr(0,1).toUpperCase()
			                  + functionName.substr(1);
			for(var i = 0, l = vendors.length; i < l; i++) {
				var vendorFn = vendors[i]+camelnotation;
				if(subject[vendorFn]) {
					implementation = subject[vendorFn];
					break;
				}
			}						
		}
	}
	
	if(!implementation && replacement) {
		implementation = replacement;
	}
	
	return implementation;
};