LUHN.js

function isCardNumberValid(cardNumber, allowSpaces) {
   if (allowSpaces) {
      cardNumber = cardNumber.replace(/ /g, '');
   }

   if (!cardNumber.match(/^\d+$/)) {
      return false;
   }

   var checksum = 0;

   for (var i = 0; i < cardNumber.length; i++) {
      var n = (cardNumber.charAt(cardNumber.length - i - 1) - '0') << (i & 1);

      checksum += n > 9 ? n - 9 : n;
   }

   return (checksum % 10) == 0 && checksum > 0;
}