XSS Payload Pattern (Basic Detection) Regex for JavaScript

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching xss payload pattern (basic detection), ported and verified for JavaScript. In security-sensitive code, using an unverified regex can open the door to both false positives and denial-of-service attacks. 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

// XSS Payload Pattern (Basic Detection)
// ReDoS-safe | RegexVault — Security > Injection Patterns

const xssPayloadPatternBasicDetectionRegex = /(?:<script[\s>]|<\\/script>|javascript:|vbscript:|onload\s*=|onerror\s*=|onclick\s*=|onmouseover\s*=|<iframe\b|<object\b|<embed\b|<svg[\s>]|document\.cookie|document\.write|eval\s*\(|setTimeout\s*\(|setInterval\s*\(|window\.location|alert\s*\(|confirm\s*\(|prompt\s*\(|data:text\/html)/i;

function validateXssPayloadPatternBasicDetection(input: string): boolean {
  return xssPayloadPatternBasicDetectionRegex.test(input);
}

// Example
console.log(validateXssPayloadPatternBasicDetection("<script>alert(1)</script>")); // true

Test Cases

When to use this pattern

This pattern is drawn from the Security > Injection Patterns 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

Basic XSS detection. Incomplete — XSS payloads can be encoded in dozens of ways (HTML entities, Unicode escapes, UTF-7, etc.). Use as a signal for logging/alerting. The real defense is output encoding via a template engine (React, Vue, Jinja2 with auto-escaping).