This repository provides a collection of functions for validating credit card numbers in JavaScript/TypeScript. The functions perform various checks to ensure that a credit card number is valid based on different criteria.

isValidLength(cardNumber: string): boolean

Checks if the length of the cardNumber string falls within the valid range for a credit card number. The valid range is between 13 and 16 digits. Returns true if the length is valid, and false otherwise.

isDigit(digit: number): boolean

Checks if the provided digit is a valid numeric digit (0-9). Returns true if the digit is valid, and false otherwise.

isNumeric(cardNumber: string): boolean

Checks if the cardNumber string consists of only numeric digits. Iterates through each character in the string and uses the isDigit function to validate each digit. Returns true if all characters are numeric, and false otherwise.

isFormulaValid(cardNumber: string): boolean

Performs the Luhn algorithm to validate the cardNumber string. The algorithm calculates a checksum by doubling every other digit, subtracting 9 if the result is greater than 9, and summing all the digits. Returns true if the checksum is divisible by 10, indicating a valid card number, and false otherwise.

isValidCreditCardNumber(cardNumber: string): boolean

Validates the cardNumber string by checking against specific card number patterns. The function uses regular expressions to match the card number against predefined patterns for different card types, including American Express, Visa, Mastercard, and Discover. Returns true if the card number matches any of the patterns, and false otherwise.

CardCheckr(cardNumber: number): boolean

Convenience function that combines multiple checks to validate a credit card number. Converts the cardNumber to a string and performs the following checks:

Validates the length using `isValidLength`.
Checks if the string consists of only numeric digits using `isNumeric`.
Performs Luhn algorithm to validate the card number using `isFormulaValid`.
Validates the card number against major US credit cards using `isValidCreditCardNumber`.

Returns true if all checks pass, indicating a valid credit card number, and false otherwise.

Feel free to use these functions to validate credit card numbers in your JavaScript/TypeScript projects. Contributions and feedback are welcome!

git clone https://github.com/p-adams/CardCheckr.git

import { CardChecker } from "./mod.ts";`

// validate Visa card
const cc = CardCheckr("4111111111111111"); // true