Install

Run npm install from root

Unit test run from root

⋅⋅* ./node_modules/.bin/karma start karma.conf.js

How the Credit Card Validator works.

How to validate a Credit Card Number?

Most credit card number can be validated using the Luhn algorithm, which is more or a less a glorified Modulo 10 formula!

The Luhn Formula:

• Drop the last digit from the number. The last digit is what we want to check against
• Reverse the numbers
• Multiply the digits in odd positions (1, 3, 5, etc.) by 2 and subtract 9 to all any result higher than 9
• Add all the numbers together
• The check digit (the last number of the card) is the amount that you would need to add to get a multiple of 10 (Modulo 10)

Luhn Example:

Step Total

1. Original Number: 4 5 5 6 7 3 7 5 8 6 8 9 9 8 5 5

2. Drop the last digit: 4 5 5 6 7 3 7 5 8 6 8 9 9 8 5

3. Reverse the digits: 5 8 9 9 8 6 8 5 7 3 7 6 5 5 4

4. Multiple odd digits by 2: 10 8 18 9 16 6 16 5 14 3 14 6 10 5 8

5. Subtract 9 to numbers over 9: 1 8 9 9 7 6 7 5 5 3 5 6 1 5 8

6. Add all numbers: 1 8 9 9 7 6 7 5 5 3 5 6 1 5 8 85

7. Mod 10: 85 modulo 10 = 5 (last digit of card)

• [Source:] (http://www.freeformatter.com/credit-card-number-generator-validator.html)