Regular Expression - IPv6 Address (#2031)

* Create script.js

* Create README.md

Author: sumanthdosapati

Specialized Areas/Regular Expressions/Validate IPv6 Address/README.md

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+# IPv6 Address Validator
+
+This snippet validates **IPv6 addresses** in both full and compressed formats using JavaScript regex.
+
+### Features
+- Supports full and shortened IPv6 formats (`::` compression)
+- Validates loopback (`::1`) and link-local (`fe80::`) addresses
+- Rejects invalid hex groups and multiple `::`
+

Specialized Areas/Regular Expressions/Validate IPv6 Address/script.js

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+// IPv6 Address Validator
+// This regex validates both full and compressed IPv6 address formats, including shorthand "::" notation.
+
+const ipv6Regex =
+  /^(?:(([0-9A-Fa-f]{1,4}:){7}[0-9A-Fa-f]{1,4})|(([0-9A-Fa-f]{1,4}:){1,7}:)|(([0-9A-Fa-f]{1,4}:){1,6}:[0-9A-Fa-f]{1,4})|(([0-9A-Fa-f]{1,4}:){1,5}(:[0-9A-Fa-f]{1,4}){1,2})|(([0-9A-Fa-f]{1,4}:){1,4}(:[0-9A-Fa-f]{1,4}){1,3})|(([0-9A-Fa-f]{1,4}:){1,3}(:[0-9A-Fa-f]{1,4}){1,4})|(([0-9A-Fa-f]{1,4}:){1,2}(:[0-9A-Fa-f]{1,4}){1,5})|([0-9A-Fa-f]{1,4}:((:[0-9A-Fa-f]{1,4}){1,6}))|(:((:[0-9A-Fa-f]{1,4}){1,7}|:)))(%.+)?$/;
+
+function validateIPv6(address) {
+  return ipv6Regex.test(address);
+}
+
+// Example usage:
+console.log(validateIPv6("2001:0db8:85a3:0000:0000:8a2e:0370:7334")); // true (full)
+console.log(validateIPv6("2001:db8:85a3::8a2e:370:7334")); // true (compressed)
+console.log(validateIPv6("::1")); // true (loopback)
+console.log(validateIPv6("fe80::")); // true (link-local)
+console.log(validateIPv6("1234:5678:9abc:def0:1234:5678:9abc:defg")); // false (invalid hex)
+console.log(validateIPv6("2001::85a3::7334")); // false (double compression)