URL Query Parameter (Single key=value) Regex for JavaScript

What this pattern does

This page provides a well-structured, multi-part regular expression for matching url query parameter (single key=value), 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 Query Parameter (Single key=value)
// ReDoS-safe | RegexVault — Web & Network > URL

const urlQueryParameterSingleKeyvalueRegex = /(?:^|[?&])([a-zA-Z][a-zA-Z0-9_\-.]{0,99})=([^&\s#]*)/g;

function validateUrlQueryParameterSingleKeyvalue(input: string): boolean {
  return urlQueryParameterSingleKeyvalueRegex.test(input);
}

// Example
console.log(validateUrlQueryParameterSingleKeyvalue("?key=value")); // 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

Use with the g flag in JS to iterate all parameters. Capture group 1 is the key, group 2 is the raw value. URL-decode values before use: decodeURIComponent(value.replace(/\+/g, ' ')).