ISO 3166-1 Alpha-2 Country Code Regex for JavaScript

What this pattern does

This page provides a lightweight, single-purpose regular expression for matching iso 3166-1 alpha-2 country code, ported and verified for JavaScript. A rigorously tested regex reduces debugging time and protects your application from edge-case failures. 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

// ISO 3166-1 Alpha-2 Country Code
// ReDoS-safe | RegexVault — Localization > Locale & Language

const iso31661Alpha2CountryCodeRegex = /^[A-Z]{2}$/;

function validateIso31661Alpha2CountryCode(input: string): boolean {
  return iso31661Alpha2CountryCodeRegex.test(input);
}

// Example
console.log(validateIso31661Alpha2CountryCode("US")); // true

Test Cases

When to use this pattern

This pattern is drawn from the Localization > Locale & Language 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

ISO 3166-1 alpha-2 uses uppercase. Exceptions: UK is not a valid code (GB is used for the United Kingdom). XK is used for Kosovo informally. EU is a special supranational code. Validate against the official ISO 3166 Maintenance Agency list.