[JavaScript] boolean return, null return

function isLess(a, b){
	return a<b;
}

console.log(isLess(10,15));
//return false


if(isLess(10,15))
	console.log("true");
else
	console.log("false");

function test(a, b){
	if(a<0 || b<0)
    	return undefined;

	return Math.round(Math.pow(Math.sqrt(a) + Math.sqrt(b), 2));
}

console.log(test(-2,2));
//null return