├── .gitignore
├── package.json
├── index.js
├── README.md
└── test.js


/.gitignore:
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1 | /node_modules
2 | 


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/package.json:
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 1 | {
 2 | 	"name": "cc-luhn",
 3 | 	"description": "Calculate or verify the credit card check digit (luhn)",
 4 | 	"version": "1.0.0",
 5 | 	"repository": "paylike/luhn",
 6 | 	"scripts": {
 7 | 		"test": "node test"
 8 | 	},
 9 | 	"devDependencies": {
10 | 		"tape": "^4.5.1"
11 | 	},
12 | 	"keywords": [ "luhn", "credit card", "validate" ],
13 | 	"license": "MIT"
14 | }
15 | 


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/index.js:
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 1 | 'use strict';
 2 | 
 3 | module.exports = luhn;
 4 | 
 5 | function luhn( a, b ){
 6 | 	if (a === true)
 7 | 		return b.slice(-1) === calculate(b.slice(0, -1));
 8 | 
 9 | 	return calculate(b || a);
10 | }
11 | 
12 | function calculate( numbers ){
13 | 	var length = numbers.length;
14 | 
15 | 	// Step 1 + 2
16 | 	var product = numbers.split('').reduce(function( p, c, i ){
17 | 		var isAlternate = (i + length) % 2 === 1;
18 | 
19 | 		return p + (isAlternate ? sumDigits((+c) * 2) : +c);
20 | 	}, 0);
21 | 
22 | 	// Step 3
23 | 	return ((10 - (product % 10)) % 10)+'';
24 | }
25 | 
26 | function sumDigits( number ){
27 | 	return (number+'').split('').reduce(sum, 0);
28 | }
29 | 
30 | function sum( a, b ){
31 | 	return +a + +b;
32 | }
33 | 


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/README.md:
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 1 | # Calculate/verify check digit (luhn) of credit cards
 2 | 
 3 | ```js
 4 | // Is the card number valid?
 5 | var card = '6123451234567893';
 6 | 
 7 | luhn(true, pan);	// true
 8 | 
 9 | 
10 | // Calculate check digit
11 | 
12 | // MII + IIN + "Individual account number"
13 | var incomplete = '612345123456789';
14 | 
15 | luhn(incomplete);	// "3"
16 | ```
17 | 
18 | Implemented according to ISO/IEC 7812-1:2015(E) which goes:
19 | 
20 | 1. Double the value of alternate digits beginning with the first right-hand
21 |    digit (low order).
22 | 
23 | 2. Add the individual digits comprising the products obtained in Step 1 to
24 |    each of the unaffected digits in the original number.
25 | 
26 | 3. Subtract the total obtained in Step 2 from the next higher number ending in
27 |    0 [this is the equivalent of calculating the “tens complement” of the
28 |    low-order digit (unit digit) of the total]. If the total obtained in Step 2
29 |    is a number ending in zero (30, 40, etc.), the check digit is 0.
30 | 


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/test.js:
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 1 | 'use strict';
 2 | 
 3 | const test = require('tape');
 4 | const luhn = require('./');
 5 | 
 6 | test(function( t ){
 7 | 	const pans = [
 8 | 		// from the ISO standard
 9 | 		'6123451234567893',
10 | 
11 | 		// http://www.paypalobjects.com/en_US/vhelp/paypalmanager_help/credit_card_numbers.htm
12 | 		'4012111111111111',
13 | 		'378282246310005',
14 | 		'371449635398431',
15 | 		'378734493671000',
16 | 		'5610591081018250',
17 | 		'30569309025904',
18 | 		'38520000023237',
19 | 		'6011111111111117',
20 | 		'6011000990139424',
21 | 		'3530111333300000',
22 | 		'3566002020360505',
23 | 		'5555555555554444',
24 | 		'5105105105105100',
25 | 		'4111111111111111',
26 | 		'4012888888881881',
27 | 		'4222222222222',
28 | 		'5019717010103742',
29 | 		'6331101999990016',
30 | 	];
31 | 
32 | 	const invalid = [
33 | 		'76009244561',
34 | 		'4571736004738485',
35 | 	];
36 | 
37 | 	pans.forEach(function( pan ){
38 | 		t.equal(luhn(true, pan), true, pan+' is valid');
39 | 		t.equal(luhn(pan.slice(0, -1)), pan.slice(-1));
40 | 	});
41 | 
42 | 	invalid.forEach(function( pan ){
43 | 		t.equal(luhn(true, pan), false, pan+' is invalid');
44 | 	});
45 | 
46 | 	t.end();
47 | });
48 | 


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