Cron Hour Field Regex for JavaScript

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching cron hour field, 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

// Cron Hour Field
// ReDoS-safe | RegexVault — Dev & Systems > Cron

const cronHourFieldRegex = /^(?:\*(?:\/[1-9]|\/1[0-9]|\/2[0-3])?|(?:[01]?[0-9]|2[0-3])(?:-(?:[01]?[0-9]|2[0-3]))?(?:\/[1-9]|\/1[0-9]|\/2[0-3])?(?:,(?:[01]?[0-9]|2[0-3]))*)$/;

function validateCronHourField(input: string): boolean {
  return cronHourFieldRegex.test(input);
}

// Example
console.log(validateCronHourField("*")); // true

Test Cases

When to use this pattern

This pattern is drawn from the Dev & Systems > Cron 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

Business hours scheduling: 9-17 for 9am-5pm. The step */6 fires at 0, 6, 12, 18.