Format credit card number

Question

How to format and validate a credit card number with spaces between each 4 digit while typing:

eg: 4464 6846 4354 3564

I have tried:

Answer 1

 9) {
        $digit-=9;
      }
    }
    // Total up the digits
    $total+=$digit;
  }

  // If the total mod 10 equals 0, the number is valid
  return ($total % 10 == 0) ? TRUE : FALSE;

}
?>