luhn

(no submodules)

Purpose

Implements the Luhn algorithm for credit-card number validation. The Luhn check is a widely-used checksum formula that can quickly determine whether a sequence of digits is plausibly a valid credit-card number, and is used here to reduce false-positive detections in the credit-card pattern module.

Features

Strips non-digit characters before validating, accepting space- or dash-separated card number formats.
O(n) implementation with no allocations beyond the cleaned digit string.
Returns false immediately for inputs shorter than 2 digits.

Usage: Basic Example

import { luhnCheck } from '@suaveplan/security-codes/utils/luhn';

luhnCheck('4532015112830366'); // true  — valid Visa test number
luhnCheck('1234567890123456'); // false — fails Luhn

Usage: Advanced Example

import { luhnCheck } from '@suaveplan/security-codes/utils/luhn';

// Space-separated card numbers are handled transparently
luhnCheck('4532 0151 1283 0366'); // true

// Short or empty strings are safely rejected
luhnCheck('');  // false
luhnCheck('4'); // false

API Reference

`luhnCheck(digits: string): boolean`

Parameter	Type	Description
`digits`	`string`	Raw digit string; non-digit chars are stripped before validation

Returns true when digits passes the Luhn checksum and contains at least two digit characters, false otherwise. Does not throw.

Implementation Notes

The algorithm doubles every second digit from the right (starting at index length - 2). When doubling produces a value greater than 9, 9 is subtracted. All digits are summed; a total divisible by 10 indicates a valid number.

This implementation intentionally avoids any dependency on built-in crypto or external libraries so that it can be used in both Node.js and browser environments without a polyfill.

The Luhn check is used by the credit-card pattern module as a secondary gate after the initial regex match. A 16-digit string matching the card-number pattern but failing the Luhn check is discarded rather than reported, which significantly reduces false positives in documents containing order IDs, tracking numbers, or other long numeric strings. Note that Luhn validation confirms mathematical plausibility only — it does not verify that the card number has ever been issued or is currently active.

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