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Luhn validation algorithm
/**
* Luhn algorithm in JavaScript: validate credit card number supplied as string of numbers
* @author ShirtlessKirk. Copyright (c) 2012.
* @license WTFPL (http://www.wtfpl.net/txt/copying)
*/
var luhnChk = (function (arr) {
return function (ccNum) {
var
len = ccNum.length,
bit = 1,
sum = 0,
val;
while (len) {
val = parseInt(ccNum.charAt(--len), 10);
sum += (bit ^= 1) ? arr[val] : val;
}
return sum && sum % 10 === 0;
};
}([0, 2, 4, 6, 8, 1, 3, 5, 7, 9]));
@ondrek
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ondrek commented Oct 14, 2013

wow! awesome! not only fast, but also beautiful code <3
thank you, dude

@storytime
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storytime commented Jun 25, 2014

Awesome!

@MohamedAlaa
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MohamedAlaa commented Jul 10, 2014

Woww! So far the Fastest Algorithm i've tried! 👍

@oPorks
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oPorks commented Jul 28, 2014

Well done!

@lagden
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lagden commented Aug 14, 2014

Fuckk Yeahhh!!!

@ShirtlessKirk
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ShirtlessKirk commented Feb 11, 2015

Spot of code golf: After reviewing subsequent edits on jsperf, I've tweaked the code. The test case is at http://jsperf.com/credit-card-validator/16 if you want to check.

  • decrement now happens inline rather than during the while conditional check (I prefer that placement)
  • reduction of product array contents to just the doubled number value as you've already got the undoubled value (less to initialise, less to look up)
  • the use of a closure to use the product array as a parameter was intriguing
  • return statement reversed to utilise short-circuiting better (if a zero length string is sent in then the sum is 0, cosmetic really)

A variant on the jsperf page doesn't run parseInt() if using the undoubled value. Personally, I don't like using it in some places and not others so I always run it. That's why this code isn't the fastest...

@ChadReitsma
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ChadReitsma commented Mar 11, 2015

Ummm, WOW. TY!!!!

@WebSellService
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WebSellService commented May 5, 2015

I am new, any one can tell me how can i use this code?
I want to validate cards.
and this code can validate all type of cards?

@lebiru
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lebiru commented May 14, 2015

+1 thanks!

@alesch
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alesch commented May 25, 2015

@geniuscarpi: Use it as luhnChk("numberToValidate").

@tomByrer
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tomByrer commented Aug 6, 2015

I'm a bit confused the reason for bit ^= 1, since it seems that bit never changes? (version Feb 11, 2015)

@jlukic
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jlukic commented Aug 13, 2015

Using an adapted version of your luhn check in our validation
Semantic-Org/Semantic-UI@2769a6e

@liqiang372
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liqiang372 commented Sep 9, 2015

Hey, I passed a test with 7 digits 2222222. Isn't valid credit card has digits range from 12 to 19? is this a bug?

@ShirtlessKirk
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ShirtlessKirk commented Oct 27, 2015

@tomByrer: yeah it does. ^= flips the value. It's a bitwise operator, not a Boolean one (see MDN page)

@CeleryCup: this is just a Luhn algorithm (see Wikipedia). Apart from checking for zero length strings there is no range checking as that is outside the scope of the method and checking for credit card number validity is just one application of it. For example, you could set up a login verification solution using identifier numbers that must pass Luhn to be valid.

@thensg
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thensg commented Nov 2, 2015

I decided to adapt your code, but add support for creating a Luhn checksum. You can find the changes here: https://gist.github.com/thensg/07bd82f73a1f784a35f0

@ChadReitsma
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ChadReitsma commented Nov 30, 2015

MasterCard announced new bin ranges (222100 - 272099) in November 2014, and will be introduced into the payment eco-system on October 2016, not sure if this validates them, but I'm assuming it will.

@enapupe
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enapupe commented Dec 2, 2015

There is a small issue regarding user input. The input MUST be a string, otherwise the return is always 0

@ShirtlessKirk
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ShirtlessKirk commented Mar 18, 2016

@enapupe: well, yeah. Credit card numbers aren't actual integers but a string of integers; every Luhn implementation expects a string to work with. Not only that, line 2 even says so...
As for returning 0, that's a falsey value, so the function still "works" ;)

@nani3105
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nani3105 commented Mar 22, 2016

Wow, Impressive

@biranchi2018
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biranchi2018 commented Sep 21, 2016

The luhn test is failing for the MasterCard BIN 2-Series (222100-272099)

Sample Master Card:
2221 0012 3412 3456,
Expiry : 12/18

@ShirtlessKirk
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ShirtlessKirk commented Oct 11, 2016

@afixibiranchi I see that your issue was answered on http://planetcalc.com/2464/ . I'm guessing you used the "number" on the example card image of https://www.mastercard.us/en-us/issuers/get-support/2-series-bin-expansion.html where it would make sense to be an invalid number...

@heymartinadams
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heymartinadams commented Sep 29, 2017

Wonderful! Thank you.

@eugene-chernogradski
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eugene-chernogradski commented Oct 26, 2017

@ShirtlessKirk OMFG
Phil, dude, who could've imagined it'would be your implementation of Luhn check I'm gonna use?!

@jonbodner
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jonbodner commented Feb 5, 2018

@ShirtlessKirk I'd like to use this luhn implementation, but my employer forbids software licensed under WTFPL. Can you relicense or dual-license under BSD or MIT?

@JurgenBlitz
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JurgenBlitz commented Jul 10, 2019

Wonderful implementation. I worked a very basic solution to adapt this algorithm to TypeScript, feel free to use or comment on improvements:
`
public luhnAlgorithmCheck(ccNum) {
const arr = [0, 2, 4, 6, 8, 1, 3, 5, 7, 9];
let len = ccNum.length;
let bit = 1;
let sum = 0;
let val;

while (len) {
  val = parseInt(ccNum.charAt(--len), 10);
  // tslint:disable-next-line:no-bitwise
  sum += (bit ^= 1) ? arr[val] : val;
}
return sum && sum % 10 === 0;

}
`
Thanks for sharing the original code, @ShirtlessKirk

@jensb1
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jensb1 commented Mar 12, 2020

"12345678".split("").reverse().map(function(c, i) { return ((i%2==0 ? 1 : 2)*parseInt(c)) }).join("").split("").map((c) => parseInt(c)).reduce(function(sum, c) { return sum+=parseInt(c) })

@emandeguzman
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emandeguzman commented Apr 23, 2020

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.

@jefelewis
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jefelewis commented Oct 1, 2021

@ShirtlessKirk What does the array at the end do?

}([0, 2, 4, 6, 8, 1, 3, 5, 7, 9]));

@ShirtlessKirk
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ShirtlessKirk commented Oct 6, 2021

@jefelewis it's a lookup table. Basically, instead of calculating the summed result of the numbers that are doubled (every second digit from right) each time, the code uses the precalculated value stored in the array at the index of the digit in question.

For example, if the digit is 6, the summed double is 3 (6 * 2 = 12, 1 + 2 = 3). In the array, the value at index 6 (the original digit used as a reference) is set to 3.

@bdr193
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bdr193 commented May 10, 2022

@ShirtlessKirk Can this be implemented in Shopify or Woocommerce? How can you install it without having access to the payment iframe

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