Japanese Date Format (YYYY年MM月DD日) Regex for JavaScript

What this pattern does

This page provides a well-structured, multi-part regular expression for matching japanese date format (yyyy年mm月dd日), 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 Date Format (YYYY年MM月DD日)
// ReDoS-safe | RegexVault — Localization > Date Formats

const japaneseDateFormatYyyymmddRegex = /^((?:19|20)[0-9]{2})年(0?[1-9]|1[0-2])月(0?[1-9]|[12][0-9]|3[01])日$/;

function validateJapaneseDateFormatYyyymmdd(input: string): boolean {
  return japaneseDateFormatYyyymmddRegex.test(input);
}

// Example
console.log(validateJapaneseDateFormatYyyymmdd("2024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

Capture groups: 1=year (western/Gregorian), 2=month, 3=day. Japan also uses its imperial era system (Reiwa/令和, Heiwa/平成, etc.) — those require separate patterns as they reset year numbering.