Japanese Imperial Era Year (Reiwa/Heisei/Showa) Regex for JavaScript

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching japanese imperial era year (reiwa/heisei/showa), 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 Imperial Era Year (Reiwa/Heisei/Showa)
// ReDoS-safe | RegexVault — Localization > Date Formats

const japaneseImperialEraYearReiwaheiseishowaRegex = /^(?:(令和|R)((?:[1-9]|[1-9][0-9]))|(平成|H)((?:[1-9]|[12][0-9]|3[01]))|(昭和|S)((?:[1-9]|[12][0-9]|3[0-9]|6[0-4])))年(0?[1-9]|1[0-2])月(0?[1-9]|[12][0-9]|3[01])日$/;

function validateJapaneseImperialEraYearReiwaheiseishowa(input: string): boolean {
  return japaneseImperialEraYearReiwaheiseishowaRegex.test(input);
}

// Example
console.log(validateJapaneseImperialEraYearReiwaheiseishowa("令和6年1月15日")); // true

Test Cases

When to use this pattern

This pattern is drawn from the Localization > Date Formats 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

Era limits: 令和/Reiwa started May 1, 2019 (max year currently ~6). 平成/Heisei: 1-31 (1989-2019). 昭和/Showa: 1-64 (1926-1989). Meiji and Taisho are pre-1926 and excluded here. Convert to Gregorian for storage.