Practice What You Learned(Javascript skills referesher)

The Luhn Algorithm

Credit card numbers can be validated with a process called the Luhn algorithm. The Luhn algorithm works like this:

1. Starting with the next to last digit and continuing with every other digit going back to the beginning of the card number, double the digit.
2. Sum all digits in the altered number.
3. If that total is a multiple of 10, the number is valid.

For example, given the card number 4408 0412 3456 7893:

Orig  :  4 4 0 8 0 4 1 2 3 4   5 6   7 8   9 3
Step 1:  8 4 0 8 0 4 2 2 6 4  10 6  14 8  18 3
Step 2:  8+4+0+8+0+4+2+2+6+4+1+0+6+1+4+8+1+8+3 = 70
Step 3:  70 % 10 == 0

Luhn Algorithm

Code

Write a function validCard that takes a number as an argument and returns true for a valid number and false for an invalid number.

validCard(1234567890123456); //should be false
validCard(4408041234567893); //should be true
validCard(38520000023237); //should be true
validCard(4222222222222); //should be true

Create A Luhn Algorithm Validator

1. A user enters a credit card in your form
2. If the Luhn Algorithm says its valid, show a message that the card is valid
3. If the Luhn Algorith says its invalid show a message that it is not valid
4. The Luhn Algo should be checking every time the state changes using the useEffect hook