ISO 8601 Week Date (YYYY-Www-D) Regex for JavaScript

What this pattern does

This page provides a well-structured, multi-part regular expression for matching iso 8601 week date (yyyy-www-d), 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

// ISO 8601 Week Date (YYYY-Www-D)
// ReDoS-safe | RegexVault — Localization > Date Formats

const iso8601WeekDateYyyywwwdRegex = /^((?:19|20)[0-9]{2})-W(0[1-9]|[1-4][0-9]|5[0-3])(?:-([1-7]))?$/;

function validateIso8601WeekDateYyyywwwd(input: string): boolean {
  return iso8601WeekDateYyyywwwdRegex.test(input);
}

// Example
console.log(validateIso8601WeekDateYyyywwwd("2024-W03")); // 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

ISO week year may differ from calendar year — the first week of the year contains the first Thursday. Week 1 starts from Monday. Day: 1=Monday, 7=Sunday. Some years have 53 weeks (ISO 8601 long years).