Make this better - phillipdornauer

jsmasterclass-exercides-1.js

// taken from http://www.dreamincode.net/code/snippet154.htm
//
// Find the weaknesses, and clean up the code.
// Find at least 3 things you can make better!
//
// Test numbers (return true):
// 4111111111111111
// 378282246310005
// 5555555555554444

function isCreditCard( CC ) {
	if (CC.length > 19)
		return false;

	var sum = 0
	   , mul = 1
	   , len = CC.length
	   , i
	   , digit
	   , tproduct;
	for (i = 0; i < len; i++)
	{
		digit = CC.substring(len - i - 1, len - i);
		tproduct = parseInt(digit ,10) * mul;
		
		if (tproduct >= 10)
			sum += (tproduct % 10) + 1;
		else
			sum += tproduct;
		
		mul += mul == 1 ? 1 : -1
	}
	return ((sum % 10) == 0);
}