Credit card validation:using JavaScript

Sample Credit Cards:

Credit card name	Valid format
American Express	378282246310005 or 371449635398431
American Express Corporate	378734493671000
Australian BankCard	5610591081018250
Diners Club	30569309025904 or 38520000023237
Discover	6011111111111117 or 6011000990139424
JCB	3530111333300000 or 3566002020360505
MasterCard	5555555555554444 or 5105105105105100
Visa	4111111111111111 or 4012888888881881 or 4222222222222* *Even though this number has a different character count than the other test numbers, it is the correct and functional number.

 
JavaScript Method:
 
 var ccErrorNo = 0;
 var ccErrors = new Array ()

 ccErrors [0] = "Unknown card type";
 ccErrors [1] = "No card number provided";
 ccErrors [2] = "Credit card number is in invalid format";
 ccErrors [3] = "Credit card number is invalid";
 ccErrors [4] = "Credit card number has an inappropriate number of digits";
 ccErrors [5] = "Warning! This credit card number is associated with a scam attempt";
 function checkCreditCard (cardnumber, cardname) {
  
   // Array to hold the permitted card characteristics
   var cards = new Array();

   // Define the cards we support. You may add addtional card types as follows.
  
   //  Name:         As in the selection box of the form - must be same as user's
   //  Length:       List of possible valid lengths of the card number for the card
   //  prefixes:     List of possible prefixes for the card
   //  checkdigit:   Boolean to say whether there is a check digit
  
   cards [0] = {name: "Visa",
       length: "13,16",
       prefixes: "4",
       checkdigit: true};
   cards [1] = {name: "MasterCard",
       length: "16",
       prefixes: "51,52,53,54,55",
       checkdigit: true};
   cards [2] = {name: "DinersClub",
       length: "14,16",
       prefixes: "36,38,54,55",
       checkdigit: true};
   cards [3] = {name: "CarteBlanche",
       length: "14",
       prefixes: "300,301,302,303,304,305",
       checkdigit: true};
   cards [4] = {name: "AmEx",
       length: "15",
       prefixes: "34,37",
       checkdigit: true};
   cards [5] = {name: "Discover",
       length: "16",
       prefixes: "6011,622,64,65",
       checkdigit: true};
   cards [6] = {name: "JCB",
       length: "16",
       prefixes: "35",
       checkdigit: true};
   cards [7] = {name: "enRoute",
       length: "15",
       prefixes: "2014,2149",
       checkdigit: true};
   cards [8] = {name: "Solo",
       length: "16,18,19",
       prefixes: "6334,6767",
       checkdigit: true};
   cards [9] = {name: "Switch",
       length: "16,18,19",
       prefixes: "4903,4905,4911,4936,564182,633110,6333,6759",
       checkdigit: true};
   cards [10] = {name: "Maestro",
       length: "12,13,14,15,16,18,19",
       prefixes: "5018,5020,5038,6304,6759,6761,6762,6763",
       checkdigit: true};
   cards [11] = {name: "VisaElectron",
       length: "16",
       prefixes: "4026,417500,4508,4844,4913,4917",
       checkdigit: true};
   cards [12] = {name: "LaserCard",
       length: "16,17,18,19",
       prefixes: "6304,6706,6771,6709",
       checkdigit: true};
      
   // Establish card type
   var cardType = -1;
   for (var i=0; i<cards.length; i++) {

  // See if it is this card (ignoring the case of the string)
  if (cardname.toLowerCase () == cards[i].name.toLowerCase()) {
    cardType = i;
    break;
  }
   }
  
   // If card type not found, report an error
   if (cardType == -1) {
   ccErrorNo = 0;
   return false;
   }
   
   // Ensure that the user has provided a credit card number
   if (cardnumber.length == 0)  {
   ccErrorNo = 1;
   return false;
   }
 
   // Now remove any spaces from the credit card number
   cardnumber = cardnumber.replace (/\s/g, "");
  
   // Check that the number is numeric
   var cardNo = cardnumber
   var cardexp = /^[0-9]{13,19}$/;
   if (!cardexp.exec(cardNo))  {
   ccErrorNo = 2;
   return false;
   }
    
   // Now check the modulus 10 check digit - if required
   if (cards[cardType].checkdigit) {
  var checksum = 0;                                  // running checksum total
  var mychar = "";                                   // next char to process
  var j = 1;                                         // takes value of 1 or 2
  
  // Process each digit one by one starting at the right
  var calc;
  for (i = cardNo.length - 1; i >= 0; i--) {
 
    // Extract the next digit and multiply by 1 or 2 on alternative digits.
    calc = Number(cardNo.charAt(i)) * j;
 
    // If the result is in two digits add 1 to the checksum total
    if (calc > 9) {
   checksum = checksum + 1;
   calc = calc - 10;
    }
 
    // Add the units element to the checksum total
    checksum = checksum + calc;
 
    // Switch the value of j
    if (j ==1) {j = 2} else {j = 1};
  }
  
  // All done - if checksum is divisible by 10, it is a valid modulus 10.
  // If not, report an error.
  if (checksum % 10 != 0)  {
   ccErrorNo = 3;
   return false;
  }
   } 
  
   // Check it's not a spam number
   if (cardNo == '5490997771092064') {
  ccErrorNo = 5;
  return false;
   }

   // The following are the card-specific checks we undertake.
   var LengthValid = false;
   var PrefixValid = false;
   var undefined;

   // We use these for holding the valid lengths and prefixes of a card type
   var prefix = new Array ();
   var lengths = new Array ();
 
   // Load an array with the valid prefixes for this card
   prefix = cards[cardType].prefixes.split(",");
   
   // Now see if any of them match what we have in the card number
   for (i=0; i<prefix.length; i++) {
  var exp = new RegExp ("^" + prefix[i]);
  if (exp.test (cardNo)) PrefixValid = true;
   }
   
   // If it isn't a valid prefix there's no point at looking at the length
   if (!PrefixValid) {
   ccErrorNo = 3;
   return false;
   }
 
   // See if the length is valid for this card
   lengths = cards[cardType].length.split(",");
   for (j=0; j<lengths.length; j++) {
  if (cardNo.length == lengths[j]) LengthValid = true;
   }
  
   // See if all is OK by seeing if the length was valid. We only check the length if all else was
   // hunky dory.
   if (!LengthValid) {
   ccErrorNo = 4;
   return false;
   };  
  
   // The credit card is in the required format.
   return true;
}
 
Source