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ValidateCreditCard.js
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63 lines (56 loc) · 2.08 KB
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/**
* Validate a given credit card number
*
* The core of the validation of credit card numbers is the Luhn algorithm.
*
* The validation sum should be completely divisible by 10 which is calculated as follows,
* every first digit is added directly to the validation sum.
* For every second digit in the credit card number, the digit is multiplied by 2.
* If the product is greater than 10 the digits of the product are added.
* This resultant digit is considered for the validation sum rather than the digit itself.
*
* Ref: https://www.geeksforgeeks.org/luhn-algorithm/
*/
const luhnValidation = (creditCardNumber) => {
let validationSum = 0
creditCardNumber.split('').forEach((digit, index) => {
let currentDigit = parseInt(digit)
if (index % 2 === 0) {
// Multiply every 2nd digit from the left by 2
currentDigit *= 2
// if product is greater than 10 add the individual digits of the product to get a single digit
if (currentDigit > 9) {
currentDigit %= 10
currentDigit += 1
}
}
validationSum += currentDigit
})
return validationSum % 10 === 0
}
const validateCreditCard = (creditCardString) => {
const validStartSubString = ['4', '5', '6', '37', '34', '35'] // Valid credit card numbers start with these numbers
if (typeof creditCardString !== 'string') {
throw new TypeError('The given value is not a string')
}
const errorMessage = `${creditCardString} is an invalid credit card number because `
if (isNaN(creditCardString)) {
throw new TypeError(errorMessage + 'it has nonnumerical characters.')
}
const creditCardStringLength = creditCardString.length
if (!(creditCardStringLength >= 13 && creditCardStringLength <= 16)) {
throw new Error(errorMessage + 'of its length.')
}
if (
!validStartSubString.some((subString) =>
creditCardString.startsWith(subString)
)
) {
throw new Error(errorMessage + 'of its first two digits.')
}
if (!luhnValidation(creditCardString)) {
throw new Error(errorMessage + 'it fails the Luhn check.')
}
return true
}
export { validateCreditCard }