function isValidCardNumber (strNum)
{
   var nCheck = 0;
   var nDigit = 0;
   var bEven = false;
   
   for (n = strNum.length - 1; n >= 0; n--) 
   {
      var cDigit = strNum.charAt (n);
      if (isDigit (cDigit))
      {
         var nDigit = parseInt(cDigit, 10);
         if (bEven)
         {
            if ((nDigit *= 2) > 9)
               nDigit -= 9;
         }
         nCheck += nDigit;
         bEven = ! bEven;
      }
      else if (cDigit != ' ' && cDigit != '.' && cDigit != '-')
      {
         return false;
      }
   }
   return (nCheck % 10) == 0;
}
function isDigit (c)
{
   var strAllowed = "1234567890";
   return (strAllowed.indexOf (c) != -1);
}

function isCardTypeCorrect (strNum, type)
{
   var nLen = 0;
   for (n = 0; n < strNum.length; n++)
   {
      if (isDigit (strNum.substring (n,n+1)))
         ++nLen;
   }
   
   if (type == 'VISA')
      return ((strNum.substring(0,1) == '4') && (nLen == 13 || nLen == 16));
   else if (type == 'American Express')
      return ((strNum.substring(0,2) == '34' || strNum.substring(0,2) == '37') && (nLen == 15));
   else if (type == 'MasterCard')
      return ((strNum.substring(0,2) == '51' || strNum.substring(0,2) == '52'
              || strNum.substring(0,2) == '53' || strNum.substring(0,2) == '54'
              || strNum.substring(0,2) == '55') && (nLen == 16));
   else if (type == 'Discover')
      return true;
   else
      return false;
   
}



/*
Validate.prototype.isValidCreditCardNumber = function(cardNumber, cardType)
{
  var isValid = false;
  var ccCheckRegExp = /[^\d ]/;
  isValid = !ccCheckRegExp.test(cardNumber);

  if (isValid)
  {
    var cardNumbersOnly = cardNumber.replace(/ /g,"");
    var cardNumberLength = cardNumbersOnly.length;
    var lengthIsValid = false;
    var prefixIsValid = false;
    var prefixRegExp;

    switch(cardType)
    {
      case "mastercard":
        lengthIsValid = (cardNumberLength == 16);
        prefixRegExp = /^5[1-5]/;
        break;

      case "visa":
        lengthIsValid = (cardNumberLength == 16 || cardNumberLength == 13);
        prefixRegExp = /^4/;
        break;

      case "amex":
        lengthIsValid = (cardNumberLength == 15);
        prefixRegExp = /^3(4|7)/;
        break;

      default:
        prefixRegExp = /^$/;
        alert("Card type not found");
    }

    prefixIsValid = prefixRegExp.test(cardNumbersOnly);
    isValid = prefixIsValid && lengthIsValid;
  }

  if (isValid)
  {
    var numberProduct;
    var numberProductDigitIndex;
    var checkSumTotal = 0;

    for (digitCounter = cardNumberLength - 1; 
      digitCounter >= 0; 
      digitCounter--)
    {
      checkSumTotal += parseInt (cardNumbersOnly.charAt(digitCounter));
      digitCounter--;
      numberProduct = String((cardNumbersOnly.charAt(digitCounter) * 2));
      for (var productDigitCounter = 0;
        productDigitCounter < numberProduct.length; 
        productDigitCounter++)
      {
        checkSumTotal += 
          parseInt(numberProduct.charAt(productDigitCounter));
      }
    }

    isValid = (checkSumTotal % 10 == 0);
  }

  return isValid;
}

*/