Luhn Algorithm in JavaScript
Implement the Luhn credit card validation algorithm in JavaScript — with full test cases.
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Tags: Luhn algorithm JavaScript, credit card validation JavaScript, Luhn check JS
Luhn Algorithm in JavaScript The Luhn algorithm is defined in ISO/IEC 7812-1. Payment card number formats and IIN (Issuer Identification Number) assignments are maintained by the ISO/IEC 7812 registration authority. For JavaScript implementation, MDN's Array methods documentation covers the core methods used. The Luhn algorithm validates identification numbers like credit card numbers and IMEI codes using a simple mod-10 checksum. Here is a complete JavaScript implementation with tests, edge case handling, and integration patterns. --- What is core implementation? What is luhn algorithm steps? | Step | Action | Example | |------|--------|---------| | 1. Reverse | Reverse digit order | 4532 → 2354 | | 2. Double every 2nd | Double every second digit | 2, 32=6, 5, 42=8 | | 3. Subtract 9 | If…
Frequently Asked Questions
How do I implement Luhn in JavaScript?
Strip non-digits with replace(/\D/g,''), reverse the array, then use reduce: at each odd index multiply by 2 and subtract 9 if over 9. Sum all digits and return sum % 10 === 0.
How do I validate a credit card number without a library?
Use the native JavaScript implementation of the Luhn algorithm — no library needed. Strip non-digit characters, apply the Luhn formula, then optionally check that the length and first digits match the expected card brand pattern.
What input sanitization is needed for Luhn?
Strip all non-digit characters before applying the Luhn formula. Card numbers are commonly entered with spaces (4111 1111 1111 1111) or dashes (4111-1111-1111-1111). After stripping, verify that the result contains only digits and has a plausible length (typically 13–19 digits for card numbers).
How do I test Luhn with known valid numbers?
Use published test card numbers from card networks: Visa 4111111111111111, Mastercard 5500000000000004, Amex 371449635398431, Discover 6011111111111117. All are Luhn-valid and are never charged by payment processors.
What are common credit card number test values?
Visa: 4111111111111111 (16 digits) and 4012888888881881. Mastercard: 5500000000000004 and 5105105105105100. Amex: 371449635398431 (15 digits). Discover: 6011111111111117. These are standardized test values that pass Luhn but are not associated with real accounts.
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