Dutch Postcode (Postcode) Regex for JavaScript

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching dutch postcode (postcode), 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

// Dutch Postcode (Postcode)
// ReDoS-safe | RegexVault — Localization > Postal Codes

const dutchPostcodePostcodeRegex = /^([1-9][0-9]{3})\s?(?!SS|SD|SA)[A-Z]{2}$/i;

function validateDutchPostcodePostcode(input: string): boolean {
  return dutchPostcodePostcodeRegex.test(input);
}

// Example
console.log(validateDutchPostcodePostcode("1234 AB")); // true

Test Cases

When to use this pattern

This pattern is drawn from the Localization > Postal Codes 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

The letter combinations SA, SD, SS are officially excluded. Some unofficial sources also exclude combinations that form offensive words in Dutch. The space is optional but conventionally present.