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 == 'Amex')
      return ((strNum.substring(0,2) == '34' || strNum.substring(0,2) == '37') && (nLen == 15));
   else if (type == 'Master Card')
      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
      return false;
   
}