Luhn algorithm in Javascript. Check valid credit card numbers

validate_credit_card.js

// Takes a credit card string value and returns true on valid number
function valid_credit_card(value) {
  // Accept only digits, dashes or spaces
	if (/[^0-9-\s]+/.test(value)) return false;

	// The Luhn Algorithm. It's so pretty.
	let nCheck = 0, bEven = false;
	value = value.replace(/\D/g, "");

	for (var n = value.length - 1; n >= 0; n--) {
		var cDigit = value.charAt(n),
			  nDigit = parseInt(cDigit, 10);

		if (bEven && (nDigit *= 2) > 9) nDigit -= 9;

		nCheck += nDigit;
		bEven = !bEven;
	}

	return (nCheck % 10) == 0;
}

awesome, thank you so much.

This is not working with Amex cards. Can anyone pls guide me. Thanks.

Nice work! Thanks!

Awesome work, thanks!

Code Works great.

Although nDigit variable declared on Line 7 is not being used[ and can be removed ] since its been redeclared inside the for loop.

Correct me if wrong @DiegoSalazar

I noticed one a little mistake in the end of the script;
If you type '0' or '00' or '0000000000' you will get true

My resolve to line 22:
return (nCheck !== 0) && (nCheck % 10) == 0

What do you think ?

ndigit is defined twice. jshint complains . line 12

Nice work, thank you!

can you explain why use the operators in nDigit -= 9; and bEven = !bEven;

@dwhyte4
bEven = !bEven is a reversal, so bEven switches between true and false on each iteration of the loop, because each even digit is doubled as per the ISO/IEC 7812 spec.
nDigit -= 9; is to bring the number back between 1 and 9 if it's a double digit number (as per the ISO/IEC 7812 spec). This is the same effect as adding the 2 digits of the number together, which is what the spec says.

See https://en.wikipedia.org/wiki/Luhn_algorithm#Description for more info.

Good job!

Thanks bro

i used to this algorithm in php master card generator script on Credit Card Generator with money and Free Credit Card Generator App. The rightmost digit is the Check digit value. We multiply the 1., 3., 5… .. values by 2, starting from the check digit value. (2nd, 4th, 6th… values remain the same.)
If the sum of the values is greater than 9, we add their numbers and find the sum of the numbers.
All the figures finally obtained are added up.
The sum of the numbers is multiplied by 9.
The last digit of the obtained number is the check digit value.

Thank you! It works nice!

I only added a validation to empty string (""), because it was returning true. Thank you a lot!

I tried this out, but I realised I was looking rather naively at my problem. This works great at evaluating the complete card number.

I wanted to evaluate the card number while it is being typed, but I found there are challenges in determining the length of card number (can range from 13 to 19 digits) preemptively.

@pranith-bm-ai You can deduce from the first few numbers what kind of credit card it is and then you'll know what its length is supposed to be, see: https://www.freeformatter.com/credit-card-number-generator-validator.html#cardFormats

I would add the line "if (!value) return false;" on top, to also take care of the situation of an empty input (or input with spaces).

I tested against https://www.paypalobjects.com/en_US/vhelp/paypalmanager_help/credit_card_numbers.htm

76009244561 did not return true

But I'm not sure if this number is really valid. all luhn verification code seem to fail when I use this number.

Working well, thank you very much Diego!

Thank you! Nice work !
I'm Getting false result for Dankort (PBS) | 76009244561

Can someone answer for me on this ?

Thanks! Great Job!
I used this Credit Card Generator and it's showing almost accurate result.
they maintained maximum bank's bin code database. you must have to visit this site.

Hi buddy,
I pull your code in my local repository, I found issues with your code It validate all types of Credit cards (like Amex, Visa, Diners Club) most of the card number are found invalid.

After that I use credit card validator on CardGenerators.com that gives me perfect result. It also validate 15, 16 and 19 digit credit cards.

The code can be rewritten as:

function valid_credit_card(value) {
  // Accept only digits, dashes or spaces
	if (/[^0-9-\s]+/.test(value)) return false;

	// The Luhn Algorithm. It's so pretty.
	let nCheck = 0;
	value = value.replace(/\D/g, "");

	for (let n = 0; n < value.length; n++) {
		let nDigit = parseInt(value[n], 10);

		if (!((n + value.length) % 2) && (nDigit *= 2) > 9) nDigit -= 9;

		nCheck += nDigit;
	}

	return (nCheck % 10) === 0;
}

Or even cleaner

export const luhn = (value) => {
    let nCheck = 0;
    if (value && /[0-9-\s]+/.test(value)) {
        value = value.replace(/\D/g, '');

        value.split('').forEach((v, n) => {
            let nDigit = parseInt(v, 10);

            if (!((value.length + n) % 2) && (nDigit *= 2) > 9) {
                nDigit -= 9;
            }

            nCheck += nDigit;
        });
    }

    return (nCheck % 10) === 0;
};

A shitty one-liner:

const luhn = numbers => numbers.split('').map((value, index) => index % 2 === 0 ? Number(value) * 2 <= 9 ? Number(value) * 2 : Number(Number(`${Number(value) * 2}`.split('')[0]) + Number(`${Number(value) * 2}`.split('')[1])) : Number(value)).reduce((a, b) => a + b).toString().split('')[1] === '0';