Domain Label (Single Segment) Regex for JavaScript

What this pattern does

This page provides a well-structured, multi-part regular expression for matching domain label (single segment), 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

// Domain Label (Single Segment)
// ReDoS-safe | RegexVault — Web & Network > Domain

const domainLabelSingleSegmentRegex = /^[a-zA-Z0-9](?:[a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])?$/;

function validateDomainLabelSingleSegment(input: string): boolean {
  return domainLabelSingleSegmentRegex.test(input);
}

// Example
console.log(validateDomainLabelSingleSegment("example")); // true

Test Cases

When to use this pattern

This pattern is drawn from the Web & Network > Domain 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 63-character maximum is per RFC 1034. The last invalid test case is 64 chars (one over the limit). Use for validating individual hostname components.