function isValidCreditCard(CCType, ccno) {
   if (CCType == "VISA") {
      // Visa: length 16, prefix 4, dashes optional.
      var re = /^4\d{3}-?\d{4}-?\d{4}-?\d{4}$/;
   } else if (CCType == "MASTERCARD") {
      // Mastercard: length 16, prefix 51-55, dashes optional.
      var re = /^5[1-5]\d{2}-?\d{4}-?\d{4}-?\d{4}$/;
   } else if (CCType == "DISCOVERY") {
      // Discover: length 16, prefix 6011, dashes optional.
      var re = /^6011-?\d{4}-?\d{4}-?\d{4}$/;
   } else if (CCType == "AMEX") {
      // American Express: length 15, prefix 34 or 37.
      var re = /^3[4,7]\d{13}$/;
   } else if (CCType == "Diners") {
      // Diners: length 14, prefix 30, 36, or 38.
      var re = /^3[0,6,8]\d{12}$/;
   } else if (CCType == "NONE"){
	  // No value.
	  var re = /^3[0,6,8]\d{12}$/;
   }
   if (!re.test(ccno)) return false;
   // Checksum ("Mod 10")
   // Add even digits in even length strings or odd digits in odd length strings.
   var checksum = 0;
   for (var i=(2-(ccno.length % 2)); i<=ccno.length; i+=2) {
      checksum += parseInt(ccno.charAt(i-1));
   }
   // Analyze odd digits in even length strings or even digits in odd length strings.
   for (var i=(ccno.length % 2) + 1; i<ccno.length; i+=2) {
      var digit = parseInt(ccno.charAt(i-1)) * 2;
      if (digit < 10) { checksum += digit; } else { checksum += (digit-9); }
   }
   if ((checksum % 10) == 0) return true; else return false;
}