URL Fragment Extraction Regex for JavaScript

What this pattern does

This page provides a lightweight, single-purpose regular expression for matching url fragment extraction, 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

// URL Fragment Extraction
// ReDoS-safe | RegexVault — Web & Network > URL

const urlFragmentExtractionRegex = /^[^#\s]+#([^\s]*)$/;

function validateUrlFragmentExtraction(input: string): boolean {
  return urlFragmentExtractionRegex.test(input);
}

// Example
console.log(validateUrlFragmentExtraction("https://example.com/page#section")); // true

Test Cases

When to use this pattern

This pattern is drawn from the Web & Network > URL 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 contains the fragment string (may be empty for bare #). Fragments are client-side only — servers never receive them.