Credit card validation not working

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   Dear gurus, 
I have a credit card script that should check for the card type and determine that a user entered correct value for the card.

For instance, Master card, Visa and Discover have 16 digits.

I am trying to ensure that if a user enters less than 16 digitis, there should be an error flag.

Similarly, if a user enters more than the required digits, he or she should be flagged.

So far, as long as the card is up to 15 digits, it is processed.

Please take a look and advise.

Thanks in advance.

<SCRIPT LANGUAGE=javascript>
<!--
// Client script validates form field entries for credit card
function validate(theForm)
 {
  if(document.cform.IsHidden.value=="false")
   {
    if (theForm.cardname.value == "" || theForm.cardname.value.length < 2)
     {
      alert("Please fill in the name found on your credit card.");
      theForm.cardname.focus() ;
      return false;
     }
     if ((theForm.paymentm = "Visa" || theForm.paymentm = "Dis" || theForm.paymentm = "MC" ) AND (theForm.cardno.value == "" || theForm.cardno.value.length < 16 || theForm.cardno.value == "0000-0000-0000-0000")
     {
      alert("Please fill in the card number in this format: 0000-0000-0000-0000.");
      theForm.cardno.focus();
      return false;
     }
     return true;
   }
 }
function isValidCreditCard(type, ccnum) {
   if (type == "Visa") {
      // Visa: length 16, prefix 4, dashes optional.
      var re = /^4\d{3}-?\d{4}-?\d{4}-?\d{4}$/;
   } else if (type == "MC") {
      // Mastercard: length 16, prefix 51-55, dashes optional.
      var re = /^5[1-5]\d{2}-?\d{4}-?\d{4}-?\d{4}$/;
   } else if (type == "Disc") {
      // Discover: length 16, prefix 6011, dashes optional.
      var re = /^6011-?\d{4}-?\d{4}-?\d{4}$/;
   } else if (type == "AmEx") {
      // American Express: length 15, prefix 34 or 37.
      var re = /^3[4,7]\d{13}$/;
   } else if (type == "Diners") {
      // Diners: length 14, prefix 30, 36, or 38.
      var re = /^3[0,6,8]\d{12}$/;
   }
   if (!re.test(ccnum)) 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-(ccnum.length % 2)); i<=ccnum.length; i+=2) {
      checksum += parseInt(ccnum.charAt(i-1));
   }
   // Analyze odd digits in even length strings or even digits in odd length strings.
   for (var i=(ccnum.length % 2) + 1; i<ccnum.length; i+=2) {
      var digit = parseInt(ccnum.charAt(i-1)) * 2;
      if (digit < 10) { checksum += digit; } else { checksum += (digit-9); }
   }
   if ((checksum % 10) == 0) return true; else return false;
}
</script>

Then I will invoke it here:

   <td width="350">
    <select name="paymentm" onChange="isValidCreditCard(this)">
     <option value="Disc">Discover</option>
     <option selected value="Visa">Visa</option>
     <option value="AmEx">American Express</option>
     <option value="MC">Mastercard</option>
     <option value="Diners">Diner's Club</option>
    </select>
   </td>

Edited by simflex - 03 December 2004 at 10:37am