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";

function checkCreditCard (cardnumber, cardname) {

     
  var cards = new Array();
  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,", 
               prefixes: "300,301,302,303,304,305,36,38",
               checkdigit: true};
  cards [3] = {name: "CarteBlanche", 
               length: "14", 
               prefixes: "300,301,302,303,304,305,36,38",
               checkdigit: true};
  cards [4] = {name: "AmEx", 
               length: "15", 
               prefixes: "34,37",
               checkdigit: true};
  cards [5] = {name: "Discover", 
               length: "16", 
               prefixes: "6011",
               checkdigit: true};
  cards [6] = {name: "JCB", 
               length: "15,16", 
               prefixes: "3,1800,2131",
               checkdigit: true};
  cards [7] = {name: "Enroute", 
               length: "15", 
               prefixes: "2014,2149",
               checkdigit: true};
               
  var cardType = -1;
  for (var i=0; i<cards.length; i++) {

    if (cardname.toLowerCase () == cards[i].name.toLowerCase()) {
      cardType = i;
      break;
    }
  }
  
  if (cardType == -1) {
     ccErrorNo = 0;
     return false; 
  }
   
  if (cardnumber.length == 0)  {
     ccErrorNo = 1;
     return false; 
  }
  
  var cardNo = cardnumber
  var cardexp = /^([0-9]{4})\s?([0-9]{4})\s?([0-9]{4})\s?([0-9]{1,4})$/;
  if (!cardexp.exec(cardNo))  {
     ccErrorNo = 2;
     return false; 
  }
    
  cardexp.exec(cardNo);
  cardNo = RegExp.$1 + RegExp.$2 + RegExp.$3 + RegExp.$4;
       
  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
  
    var calc;
    for (i = cardNo.length - 1; i >= 0; i--) {
    
      calc = Number(cardNo.charAt(i)) * j;
    
      if (calc > 9) {
        checksum = checksum + 1;
        calc = calc - 10;
      }
    
      checksum = checksum + calc;
    
      if (j ==1) {j = 2} else {j = 1};
    } 
  
    if (checksum % 10 != 0)  {
     ccErrorNo = 3;
     return false; 
    }
  }  

  var LengthValid = false;
  var PrefixValid = false; 
  var undefined; 

  var prefix = new Array ();
  var lengths = new Array ();
    
  prefix = cards[cardType].prefixes.split(",");
      
  for (i=0; i<prefix.length; i++) {
    var exp = new RegExp ("^" + prefix[i]);
    if (exp.test (cardNo)) PrefixValid = true;
  }
      
  if (!PrefixValid) {
     ccErrorNo = 3;
     return false; 
  }
    
  lengths = cards[cardType].length.split(",");
  for (j=0; j<lengths.length; j++) {
    if (cardNo.length == lengths[j]) LengthValid = true;
  }
  
  if (!LengthValid) {
     ccErrorNo = 4;
     return false; 
  };   
  
  return true;
}