Credit card numbers can be validated with a process called the Luhn algorithm. The Luhn algorithm works like this:
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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.
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Sum all digits in the altered number.
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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
Write a function validCard that takes a number as an argument and returns true for a valid number and false for an invalid number.
console.log(validCard(1234567890123456)); #should be false
console.log(validCard(4408041234567893)); #should be true
console.log(validCard(38520000023237)); #should be true
console.log(validCard(4222222222222)); #should be true