Bank Card Validation Tests

luhn.js

function luhn_checksum( cardNumber ) {
  var checkDigit = cardNumber % 10;
  var checksumNumber = parseInt( cardNumber / 10 ).toString();
  var digits = checksumNumber.length;
  
  var sum = 0,
      digit,
      tempNumber;
  
  for ( var i = 0; i < digits; i++ ) {
    var digit = parseFloat( cardNumber[i] );
    if ( i % 2 === 1 ) {
      tempNumber = digit * 2;
      tempNumber += '';
      for ( var j = 0; j < tempNumber.length; j++ ) {
        sum += parseFloat( tempNumber[j] );
      }
    }
    else {
      sum += digit;
    }
  }

  var calculatedCheckDigit = parseInt( ( sum * 9 ) % 10 );
  return ( calculatedCheckDigit - checkDigit );
}

function is_luhn_valid( cardNumber ) {
  return ( luhn_checksum( cardNumber ) == 0 );
}