File Extension Extraction Regex for JavaScript

What this pattern does

This page provides a well-structured, multi-part regular expression for matching file extension 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

// File Extension Extraction
// ReDoS-safe | RegexVault — Dev & Systems > File Paths

const fileExtensionExtractionRegex = /(?:^|\\/)([^\\/\s\.]+[\w.]*\.([a-zA-Z0-9]{1,10}))$/i;

function validateFileExtensionExtraction(input: string): boolean {
  return fileExtensionExtractionRegex.test(input);
}

// Example
console.log(validateFileExtensionExtraction("file.txt")); // true

Test Cases

When to use this pattern

This pattern is drawn from the Dev & Systems > File Paths 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

Group 1 = final extension segment. For compound extensions like .tar.gz, extract the last segment (gz). Extension limited to 10 chars. Dotfiles (.gitignore) have no extension.