JavaScript Luhn modulus implementation

Plan Zero — Wed, 26 Aug 2009 21:43:01 +0000

The following luhn_check() function is a small JavaScript function which checks whether a number is a valid based on the Luhn algoritm. One common example of use is with credit and debit card numbers. This function may be used to check for valid credit card numbers, however additional checks may be desired, such as card prefix and length checks.

There’s a working example of this function to give you more of an idea of how it works!

/* Luhn algorithm number checker - (c) 2005-2009 - planzero.org            *
 * This code has been released into the public domain, however please      *
 * give credit to the original author where possible.                      */
 
function luhn_check(number) {
//
 
  // Strip any non-digits (useful for credit card numbers with spaces and hyphens)
  var number=number.replace(/\D/g, '');
 
  // Set the string length and parity
  var number_length=number.length;
  var parity=number_length % 2;
 
  // Loop through each digit and do the maths
  var total=0;
  for (i=0; i < number_length; i++) {
    var digit=number.charAt(i);
    // Multiply alternate digits by two
    if (i % 2 == parity) {
      digit=digit * 2;
      // If the sum is two digits, add them together (in effect)
      if (digit > 9) {
        digit=digit - 9;
      }
    }
    // Total up the digits
    total = total + parseInt(digit);
  }
 
  // If the total mod 10 equals 0, the number is valid
  if (total % 10 == 0) {
    return true;
  } else {
    return false;
  }
 
//]]>
}

PHP Luhn modulus implementation

Plan Zero — Wed, 26 Aug 2009 21:28:51 +0000

The following luhn_check() function is a small PHP function which checks whether a number is a valid based on the Luhn algorithm. One common example of use is with credit and debit card numbers. This function may be used to check for valid credit card numbers, however additional checks may be desired, such as card prefix and length checks.


/* Luhn algorithm number checker - (c) 2005-2008 - planzero.org            *
 * This code has been released into the public domain, however please      *
 * give credit to the original author where possible.                      */
 
function luhn_check($number) {
 
  // Strip any non-digits (useful for credit card numbers with spaces and hyphens)
  $number=preg_replace('/\D/', '', $number);
 
  // Set the string length and parity
  $number_length=strlen($number);
  $parity=$number_length % 2;
 
  // Loop through each digit and do the maths
  $total=0;
  for ($i=0; $i<$number_length; $i++) {
    $digit=$number[$i];
    // Multiply alternate digits by two
    if ($i % 2 == $parity) {
      $digit*=2;
      // If the sum is two digits, add them together (in effect)
      if ($digit > 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;
 
}
 
?>

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JavaScript Luhn modulus implementation

PHP Luhn modulus implementation