Luhn's Algorithm

Javascript implementation of Luhn's Algorithm used for checking the validity of a Credit/Debit card 16 digit number.

Usage

const DebitCard = new Card();
let Check = DebitCard.Check('4929207313500168')
console.log(Check)

How does it work

Luhn's algorithm uses the pattern of 2 1 2 1 to multiply corresponding numbers by the pattern numbers they are assigned too.

Card Number:  4 9 2 9 2 0 7 3 1 3 5 0 0 1 6 8 
Pattern used: 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1
Answer:       8 9 4 9 4 0 5 3 2 3 1 0 0 1 3 8

If an answer goes into double digits, the answer will be split into two single digits and they will be added together; for example, 6 * 2 = 12 so we split 12 into 1 + 2 = 3. If a card number is valid it must end in a zero.

The Sum of adding up 8 9 4 9 4 0 5 3 2 3 1 0 0 1 3 8 is 60, therefore the card is a valid card. This doesn't mean the card is active or was ever active but merely means it fits the algorithm.

Disclaimer

This doesn't poll or check any external service and only uses the algorithm to check its validity, it's very possible that a number could be used that passes this test but still isn't a valid card number.