Japanese Postal Code (〒XXX-XXXX) Regex for JavaScript

What this pattern does

This page provides a lightweight, single-purpose regular expression for matching japanese postal code (〒xxx-xxxx), 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

// Japanese Postal Code (〒XXX-XXXX)
// ReDoS-safe | RegexVault — Localization > Postal Codes

const japanesePostalCodeXxxxxxxRegex = /^〒?([0-9]{3})-?([0-9]{4})$/;

function validateJapanesePostalCodeXxxxxxx(input: string): boolean {
  return japanesePostalCodeXxxxxxxRegex.test(input);
}

// Example
console.log(validateJapanesePostalCodeXxxxxxx("100-0001")); // 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

Capture group 1: 3-digit regional code, group 2: 4-digit local code. The 〒 symbol (postal mark) is optional in digital contexts. 100-0001 is Tokyo (Chiyoda ward). Japan Post maintains the authoritative address database.