JavaScript card PAN check digit Luhn verification

Asked 3/5, 2011 at 12:41 Answered 4/9, 2015 at 8:33

I've used the code from the link below to try and validate a credit card, however I'm not getting an alert when I submit a the wrong data in the field.

Strip spaces before performing Luhn check

my form is as follows:

<form id="myform" method="post" action=""> 

<p>Select credit card:
   <select tabindex="11" id="CardType"> 
      <option value="AmEx">American Express</option> 
    <option value="CarteBlanche">Carte Blanche</option> 
    <option value="DinersClub">Diners Club</option> 
    <option value="Discover">Discover</option> 
    <option value="EnRoute">enRoute</option> 
    <option value="JCB">JCB</option> 
    <option value="Maestro">Maestro</option> 
    <option value="MasterCard">MasterCard</option> 
    <option value="Solo">Solo</option> 
    <option value="Switch">Switch</option> 
    <option value="Visa">Visa</option> 
    <option value="VisaElectron">Visa Electron</option> 
    <option value="LaserCard">Laser</option> 
  </select> 
</p>

<p>
Enter number:
 <input type="text" id="CardNumber" maxlength="24" size="24" />
  <input type="submit" id="submitbutton" onsubmit="Validate(Luhn);" />  
</p> 

</form>

Maybe I'm using the wrong code?

Charin answered 3/5, 2011 at 12:41 Comment(0)

move onsubmit="Validate(Luhn);"

to the form tag and pass the form

Like this - note I pass the form and find the number from the form. I also moved the test and return false/return true around

http://jsfiddle.net/mplungjan/VqXss/

function Validate(theForm) {
  var Luhn = theForm.CardNumber.value;
  var LuhnDigit = parseInt(Luhn.substring(Luhn.length-1,Luhn.length));
  var LuhnLess = Luhn.substring(0,Luhn.length-1);
  if (Calculate(LuhnLess)!=parseInt(LuhnDigit)) {
    alert("\n\nYou have mis-typed your card number! \nPlease check and correct.\n\n")   
    return false;
  }
  return true;
}
</script>
</head>
<body>
<form id="myform" method="post" action="" onsubmit="return Validate(this)">

Leaper answered 3/5, 2011 at 12:46 Comment(2)

thanks for your response...i copied the above code however the form seems to just submit regardless. – Charin 3/5, 2011 at 13:11

you are welcome... Now see my other answer to your submit button issue – Leaper 3/5, 2011 at 16:24

I came to this question looking for online card PAN validator in javascript that can be safely used to verify PAN check digit without risk of malicious intercept on server.

There are plenty of javascript Luhn implementations at http://rosettacode.org/wiki/Luhn_test_of_credit_card_numbers#JavaScript and https://sites.google.com/site/abapexamples/javascript/luhn-validation.

Here is typical implementation:

var LuhnCheck = (function()
{
    var luhnArr = [0, 2, 4, 6, 8, 1, 3, 5, 7, 9];
    return function(str)
    {
        var counter = 0;
        var incNum;
        var odd = false;
        var temp = String(str).replace(/[^\d]/g, "");
        if ( temp.length == 0)
            return false;
        for (var i = temp.length-1; i >= 0; --i)
        {
            incNum = parseInt(temp.charAt(i), 10);
            counter += (odd = !odd)? incNum : luhnArr[incNum];
        }
        return (counter%10 == 0);
    }
})();

And by googling for "luhn jsfiddle" I've found another ready to use robust online validator:

http://jsfiddle.net/silvinci/84bru/light/

Witkin answered 4/9, 2015 at 8:33 Comment(0)

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