Validate Credit Card Numbers Instantly Validate credit card numbers using the Luhn algorithm with card network detection.

The tool works by using the Luhn algorithm, implemented in the `luhnCheck` function, which takes a string of digits as input and returns a boolean indicating whether the number passes the checksum test. This is done by iterating over the digits from right to left, doubling every second digit, and subtracting 9 if the result is greater than 9. The sum of these modified digits is then checked to see if it's divisible by 10, which determines the validity of the credit card number. The `validateCard` function uses this algorithm in conjunction with a set of predefined patterns for different card networks, such as Visa and Mastercard, to identify the type of card and validate its length.

The tool also utilizes React state management, specifically the `useState` hook, to store the user's input and the validation result. The `useCallback` hook is used to memoize the `handleValidate` function, which is called when the user clicks the "Validate" button or presses Enter. This function updates the component's state with the result of the validation, which is then rendered in the UI. The tool uses Framer Motion for animations and React components such as `InputWithHelp` and `CopyButton` to handle user input and provide a masked version of the credit card number.

The patterns for different card networks are defined in the `CARD_PATTERNS` array, which contains objects with properties such as `name`, `pattern`, and `lengths`. These patterns are used to identify the type of card and validate its length. For example, the pattern for Visa cards is `/^4/`, which matches any string that starts with the digit 4. The lengths property specifies the valid lengths for each card network, such as 13, 16, or 19 digits for Visa cards. The tool uses JavaScript's built-in `RegExp` object to match these patterns against the user's input.

The component also uses a combination of CSS classes and inline styles to render the validation result, including a colored indicator (green for valid, red for invalid) and a list of detailed feedback messages. These messages are generated based on the validation result and include information such as whether the card number passes the Luhn checksum, its type, and its masked version. The tool's UI is built using HTML elements such as `div`, `input`, and `button`, which are styled using CSS classes defined in the component's stylesheet.

The tool's implementation relies on JavaScript's string manipulation methods, such as `replace` and `test`, to process the user's input and validate it against the predefined patterns. The `validateCard` function returns an object with properties such as `valid`, `cardType`, and `details`, which contain information about the validation result. This object is then used to update the component's state and render the validation result in the UI. Overall, the tool provides a robust and accurate way to validate credit card numbers, using a combination of algorithms, React components, and CSS styles to provide a user-friendly interface.