Credit Card JS
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// Before a credit card is submitted to a financial institution, it generally
// makes sense to run some simple reality checks on the number.
// The numbers are a good length and it's common to make minor
// transcription errors when the card is not scanned directly.
// The first check people often do is to validate that the card
// matches a known pattern from one of the accepted card providers.
// Here's how to validate if a card is valid or not:
// - Starting with the first digit and continuing with every other digit, multiply by 2
// - Sum all doubled and untouched digits in the number
// - If that sum is a multiple of 10, the number is valid
// For example, given the card number 4408 0412 3456 7893:
// Step 0: 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
// That card is valid.
// One more example, 4417 1234 5678 9112:
// Step 0: 4 4 1 7 1 2 3 4 5 6 7 8 9 1 1 2
// Step 1: 8 4 2 7 2 2 6 4 10 6 14 8 18 1 2 2
// Step 2: 8+4+2+7+2+2+6+4+1+0+6+1+4+8+1+8+1+2+2 = 69
// Step 3: 69 % 10 != 0
// Write a function `isValidCC(ccnum)` that takes a string and
// returns `true` if the credit card entered is valid, `false` otherwise.
function isValid(ccnum){}
// tests
// ---
console.assert(isValid("4408 0412 3456 7893") === false)
console.assert(isValid("5000000000000000") === false)
JavaScript
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