IPv4-Mapped IPv6 Address Regex for JavaScript

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching ipv4-mapped ipv6 address, 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

// IPv4-Mapped IPv6 Address
// ReDoS-safe | RegexVault — Web & Network > IPv6

const ipv4mappedIpv6AddressRegex = /^::(?:ffff:)?(?:(?:25[0-5]|2[0-4][0-9]|1[0-9]{2}|[1-9][0-9]|[0-9])\.){3}(?:25[0-5]|2[0-4][0-9]|1[0-9]{2}|[1-9][0-9]|[0-9])$/i;

function validateIpv4mappedIpv6Address(input: string): boolean {
  return ipv4mappedIpv6AddressRegex.test(input);
}

// Example
console.log(validateIpv4mappedIpv6Address("::ffff:192.168.1.1")); // true

Test Cases

When to use this pattern

This pattern is drawn from the Web & Network > IPv6 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

Used when a dual-stack socket receives an IPv4 connection. The ::ffff: prefix indicates the IPv4-mapped form. Without ffff, it is an IPv4-compatible address (deprecated per RFC 4291).