Credit Card Validation

gistfile1.js

// thanks to http://datagenetics.com/blog/july42013/index.html
function mod10_check(val){
	var nondigits = new RegExp(/[^0-9]+/g);
	var number = val.replace(nondigits,'');
	var pos, digit, i, sub_total, sum = 0;
	var strlen = number.length;
	if(strlen < 13){ return false; }
	for(i=0;i<strlen;i++){
		pos = strlen - i;
		digit = parseInt(number.substring(pos - 1, pos));
		if(i % 2 == 1){
			sub_total = digit * 2;
			if(sub_total > 9){
				sub_total = 1 + (sub_total - 10);
			}
		} else {
			sub_total = digit;
		}
		sum += sub_total;
	}
	if(!sum){ return false; }
	if(sum % 10 == 0){
		return true;
	}
	return false;
}