Port in URL Context (:port) Regex for JavaScript

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching port in url context (:port), 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

// Port in URL Context (:port)
// ReDoS-safe | RegexVault — Web & Network > Port

const portInUrlContextPortRegex = /:(?:6553[0-5]|655[0-2][0-9]|65[0-4][0-9]{2}|6[0-4][0-9]{3}|[1-5][0-9]{4}|[1-9][0-9]{0,3})(?=[\/?#\s]|$)/;

function validatePortInUrlContextPort(input: string): boolean {
  return portInUrlContextPortRegex.test(input);
}

// Example
console.log(validatePortInUrlContextPort(":80")); // true

Test Cases

When to use this pattern

This pattern is drawn from the Web & Network > Port 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

The lookahead (?=[/?#\s]|$) ensures the port is not followed by other URL characters that would indicate it is part of a different token. Go requires a separate bounds check.