Design by contract in javascript

gistfile1.js

//Design by contract function
function $contracted(pre, post, func){
	return function(){
		var paramsAsArray,
			funcName,
			retVal;
		
		paramsAsArray = Array.slice(arguments)
		funcName = func.toString().substr('function '.length);
		funcName = funcName.substr(0, funcName.indexOf('('));//strip of everything, but the name

		if (!pre.apply(this, paramsAsArray)){
			console.error("pre condition failed for '",func,"' with: ",paramsAsArray);
			throw "pre condition failed for '"+ funcName+"'";
		} else {
			retVal = func.apply(this, paramsAsArray);
			if (!post(retVal)){
				console.error("post condition failed for '",func,"'. It returned '",retVal,"' with: ",paramsAsArray);
				throw "post condition failed for '"+ funcName+"'";
			}
			return retVal;
		}
	}
}

//Example:
var doSomething = $contracted(
	function pre(a,b,c) b > 0, //javascript 1.8 needed for the fancy lambda syntax. else write: function pre(a,b,c){return b>0 }
	function post(r) r > 0,

	function doSomething(a,b,c){
		return a + (c / b);
	}
);

doSomething(1,2,3);
doSomething(0,0,0);
doSomething(0,3,0);