Long Form Date (Month Name, English) Regex for JavaScript

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching long form date (month name, english), 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

// Long Form Date (Month Name, English)
// ReDoS-safe | RegexVault — Localization > Date Formats

const longFormDateMonthNameEnglishRegex = /^(?:((?:[0-2]?[0-9]|3[01])(?:st|nd|rd|th)?)\s+(January|February|March|April|May|June|July|August|September|October|November|December)\s+((?:19|20)[0-9]{2})|(January|February|March|April|May|June|July|August|September|October|November|December)\s+([0-2]?[0-9]|3[01])(?:st|nd|rd|th)?,?\s+((?:19|20)[0-9]{2}))$/i;

function validateLongFormDateMonthNameEnglish(input: string): boolean {
  return longFormDateMonthNameEnglishRegex.test(input);
}

// Example
console.log(validateLongFormDateMonthNameEnglish("15 January 2024")); // 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

Matches both UK order (D Month Y) and US order (Month D, Y). The ordinal suffix (st, nd, rd, th) is optional. Month names are case-insensitive. Abbreviated month names (Jan, Feb) require a different pattern.