Masked Card Number (PAN Masking) Regex for JavaScript

What this pattern does

This page provides a well-structured, multi-part regular expression for matching masked card number (pan masking), ported and verified for JavaScript. Financial data validation has zero tolerance for false negatives — a missed invalid entry can corrupt downstream calculations. The snippet below is ready to drop into your JavaScript project — whether you're validating in an Express middleware, a Next.js API route, or a client-side form.

Javascript Implementation

// Masked Card Number (PAN Masking)
// ReDoS-safe | RegexVault — Finance > Card Numbers

const maskedCardNumberPanMaskingRegex = /^[X*]{12}[0-9]{4}$|^[X*]{8}[0-9]{4}$|^[X*]{11}[0-9]{4}$/;

function validateMaskedCardNumberPanMasking(input: string): boolean {
  return maskedCardNumberPanMaskingRegex.test(input);
}

// Example
console.log(validateMaskedCardNumberPanMasking("XXXXXXXXXXXX1234")); // true

Test Cases

When to use this pattern

This pattern is drawn from the Finance > Card Numbers category and carries a ReDoS-safe certification. That matters for JavaScript developers because especially critical in long-running Node.js event loops where a ReDoS vulnerability can block the entire process. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

Technical Notes

PCI-DSS allows displaying first 6 and last 4 digits for debugging. This pattern shows only last 4. For display in UI, use: [\*X]{8,12}[0-9]{4} adjusted for 13/15/16-digit cards.