Thai Postal Code Regex for JavaScript

What this pattern does

This page provides a lightweight, single-purpose regular expression for matching thai postal 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

// Thai Postal Code
// ReDoS-safe | RegexVault — Localization > Postal Codes

const thaiPostalCodeRegex = /^([1-9][0-9])[0-9]{3}$/;

function validateThaiPostalCode(input: string): boolean {
  return thaiPostalCodeRegex.test(input);
}

// Example
console.log(validateThaiPostalCode("10110")); // 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

Thai postal codes: 10xxx (Bangkok), 20xxx-27xxx (Eastern region), 30xxx-39xxx (Northeast), 40xxx-49xxx (North/Northeast), 50xxx-58xxx (North), 60xxx-67xxx (Lower North), 70xxx-77xxx (West), 80xxx-86xxx (South). Thailand Post manages the database.