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| ## ip-address | |
| `ip-address` is a library for validating and manipulating IPv4 and IPv6 addresses in JavaScript and TypeScript. | |
| ### Install | |
| ```sh | |
| npm install ip-address | |
| ``` | |
| ### Examples | |
| ```ts | |
| import { Address4, Address6 } from 'ip-address'; | |
| // Validation | |
| Address4.isValid('192.168.1.1'); // true | |
| Address6.isValid('2001:db8::1'); // true | |
| Address6.isValid('not an address'); // false | |
| // Parsing (throws AddressError on invalid input) | |
| const v4 = new Address4('192.168.1.1/24'); | |
| const v6 = new Address6('2001:db8::1/64'); | |
| // Subnet membership | |
| const host = new Address4('192.168.1.42'); | |
| const network = new Address4('192.168.1.0/24'); | |
| host.isInSubnet(network); // true | |
| // Subnet range | |
| network.startAddress().correctForm(); // '192.168.1.0' | |
| network.endAddress().correctForm(); // '192.168.1.255' | |
| // Strict network-address check (host bits must be zero). | |
| // isValid() accepts CIDRs with host bits set — '192.168.1.5/24' is a valid | |
| // host-with-subnet, but it isn't a network address. | |
| const cidr = new Address4('192.168.1.5/24'); | |
| Address4.isValid('192.168.1.5/24'); // true | |
| cidr.correctForm() === cidr.startAddress().correctForm(); // false | |
| // Address properties | |
| const link = new Address6('fe80::1'); | |
| link.isLinkLocal(); // true | |
| link.isMulticast(); // false | |
| link.isLoopback(); // false | |
| new Address4('192.168.1.1').isPrivate(); // true (RFC 1918) | |
| new Address6('fc00::1').isULA(); // true (RFC 4193) | |
| // Numeric and byte representations | |
| v4.bigInt(); // 3232235777n | |
| v4.toArray(); // [192, 168, 1, 1] | |
| v6.canonicalForm(); // '2001:0db8:0000:0000:0000:0000:0000:0001' | |
| // Embedded IPv4 + Teredo | |
| const teredo = new Address6('2001:0:ce49:7601:e866:efff:62c3:fffe'); | |
| teredo.inspectTeredo().client4; // '157.60.0.1' | |
| // Parse host + port from a URL | |
| Address6.fromURL('http://[2001:db8::1]:8080/').port; // 8080 | |
| ``` | |
| ### Features | |
| - Written in TypeScript with full type definitions; usable from CommonJS and ESM | |
| - Zero runtime dependencies | |
| - Parses all standard IPv4 and IPv6 notations, including subnets and zones | |
| - Parses IPv6 hosts (and ports) from URLs via `Address6.fromURL(url)` | |
| - Subnet membership checks (`isInSubnet`) and range queries (`startAddress` / `endAddress`) | |
| - Special-property checks: private (RFC 1918) / ULA (RFC 4193), loopback, link-local, multicast, broadcast, unspecified, CGNAT, documentation, Teredo, 6to4, v4-in-v6 | |
| - Decodes [Teredo](http://en.wikipedia.org/wiki/Teredo_tunneling#IPv6_addressing) and 6to4 tunneling information | |
| - Conversions: canonical/correct form, hex, binary, decimal, byte arrays, BigInt, `in-addr.arpa` / `ip6.arpa` | |
| - Runs in Node.js and the browser | |
| - Thousands of test cases | |
| ### Terminology | |
| A few terms used throughout the API can be confusing if you haven't worked deeply with IPv6 before: | |
| - **Correct form** — the shortest valid representation, per [RFC 5952](https://datatracker.ietf.org/doc/html/rfc5952): leading zeros stripped, the longest run of zero groups collapsed to `::`, and hex digits lowercased (e.g. `2001:db8::1`). This is what most software displays. | |
| - **Canonical form** — the fully expanded representation: all 8 groups, each padded to 4 hex digits, no `::` collapsing (e.g. `2001:0db8:0000:0000:0000:0000:0000:0001`). Useful for sorting and byte-exact comparison. | |
| - **Subnet** — the network portion of an address expressed as a CIDR prefix length (e.g. `/24` for IPv4, `/64` for IPv6). `startAddress()` / `endAddress()` return the bounds of the subnet's range. | |
| - **Zone** — the IPv6 scope identifier appended after `%`, used to disambiguate link-local addresses across interfaces (e.g. `fe80::1%eth0`). | |
| - **v4-in-v6** — mixed notation that embeds an IPv4 address as the last 32 bits of an IPv6 address, e.g. `::ffff:192.168.0.1`. Used for IPv4-mapped IPv6 addresses. | |
| - **Teredo** — a tunneling protocol that encodes an IPv4 endpoint, port, and flags inside a `2001::/32` IPv6 address. `inspectTeredo()` decodes those fields. | |
| - **6to4** — a tunneling protocol that embeds an IPv4 address as the second 16 bits of a `2002::/16` IPv6 address. `inspect6to4()` decodes the embedded v4 address. | |
| ### API | |
| <!-- API:START --> | |
| #### AddressError | |
| **Constructor** | |
| - `new AddressError(message: string, parseMessage?: string): AddressError` | |
| **Properties** | |
| - `parseMessage: string` — [src](https://github.com/beaugunderson/ip-address/blob/master/src/address-error.ts#L2) | |
| #### Address4 | |
| Represents an IPv4 address | |
| **Constructor** | |
| - `new Address4(address: string): Address4` | |
| **Static methods** | |
| - `static isValid(address: string): boolean` — Returns true if the given string is a valid IPv4 address (with optional CIDR subnet), false otherwise. Host bits in the subnet portion are allowed (e.g. `192.168.1.5/24` is valid); for strict network-address validation compare `correctForm()` to `startAddress().correctForm()`, or use `networkForm()`. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L53) | |
| - `static fromAddressAndMask(address: string, mask: string): Address4` — Construct an `Address4` from an address and a dotted-decimal subnet mask given as separate strings (e.g. as returned by Node's `os.networkInterfaces()`). Throws `AddressError` if the mask is non-contiguous (e.g. `255.0.255.0`). [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L104) | |
| - `static fromAddressAndWildcardMask(address: string, wildcardMask: string): Address4` — Construct an `Address4` from an address and a Cisco-style wildcard mask given as separate strings (e.g. `0.0.0.255` for a `/24`). The wildcard mask is the bitwise inverse of the subnet mask. Throws `AddressError` if the mask is non-contiguous (e.g. `0.255.0.255`). [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L118) | |
| - `static fromWildcard(input: string): Address4` — Construct an `Address4` from a wildcard pattern with trailing `*` octets. The number of trailing wildcards determines the prefix length: each `*` represents 8 bits. Only trailing whole-octet wildcards are supported. Partial-octet wildcards (e.g. `192.168.0.1*`) and interior wildcards (e.g. `192.*.0.1`) throw `AddressError`. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L140) | |
| - `static fromHex(hex: string): Address4` — Converts a hex string to an IPv4 address object. Accepts 8 hex digits with optional `:` separators (e.g. `'7f000001'` or `'7f:00:00:01'`). Throws `AddressError` for any other length or for non-hex characters. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L175) | |
| - `static fromInteger(integer: number): Address4` — Converts an integer into a IPv4 address object. The integer must be a non-negative safe integer in the range `[0, 2**32 - 1]`; otherwise `AddressError` is thrown. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L198) | |
| - `static fromArpa(arpaFormAddress: string): Address4` — Return an address from in-addr.arpa form [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L214) | |
| - `static fromBigInt(bigInt: bigint): Address4` — Converts a BigInt to a v4 address object. The value must be in the range `[0, 2**32 - 1]`; otherwise `AddressError` is thrown. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L361) | |
| - `static fromByteArray(bytes: number[]): Address4` — Convert a byte array to an Address4 object. To convert from a Node.js `Buffer`, spread it: `Address4.fromByteArray([...buf])`. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L376) | |
| - `static fromUnsignedByteArray(bytes: number[]): Address4` — Convert an unsigned byte array to an Address4 object [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L396) | |
| **Instance methods** | |
| - `parse(address: string): string[]` — Parses an IPv4 address string into its four octet groups and stores the result on `this.parsedAddress`. Called automatically by the constructor; you typically don't need to call it directly. Throws `AddressError` if the input is not a valid IPv4 address. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L70) | |
| - `correctForm(): string` — Returns the address in correct form: octets joined with `.` and any leading zeros stripped (e.g. `192.168.1.1`). For IPv4 this matches the canonical dotted-decimal representation. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L85) | |
| - `toHex(): string` — Converts an IPv4 address object to a hex string [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L227) | |
| - `toArray(): number[]` — Converts an IPv4 address object to an array of bytes. To get a Node.js `Buffer`, wrap the result: `Buffer.from(address.toArray())`. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L237) | |
| - `toGroup6(): string` — Converts an IPv4 address object to an IPv6 address group [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L245) | |
| - `bigInt(): bigint` — Returns the address as a `bigint` [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L264) | |
| - `startAddress(): Address4` — The first address in the range given by this address' subnet. Often referred to as the Network Address. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L281) | |
| - `startAddressExclusive(): Address4` — The first host address in the range given by this address's subnet ie the first address after the Network Address [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L290) | |
| - `endAddress(): Address4` — The last address in the range given by this address' subnet Often referred to as the Broadcast [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L308) | |
| - `endAddressExclusive(): Address4` — The last host address in the range given by this address's subnet ie the last address prior to the Broadcast Address [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L317) | |
| - `subnetMaskAddress(): Address4` — The dotted-decimal form of the subnet mask, e.g. `255.255.240.0` for a `/20`. Returns an `Address4`; call `.correctForm()` for the string. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L327) | |
| - `wildcardMask(): Address4` — The Cisco-style wildcard mask, e.g. `0.0.0.255` for a `/24`. This is the bitwise inverse of `subnetMaskAddress()`. Returns an `Address4`; call `.correctForm()` for the string. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L339) | |
| - `networkForm(): string` — The network address in CIDR string form, e.g. `192.168.1.0/24` for `192.168.1.5/24`. For an address with no explicit subnet the prefix is `/32`, e.g. `networkForm()` on `192.168.1.5` returns `192.168.1.5/32`. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L351) | |
| - `mask(mask?: number): string` — Returns the first n bits of the address, defaulting to the subnet mask [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L410) | |
| - `getBitsBase2(start: number, end: number): string` — Returns the bits in the given range as a base-2 string [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L422) | |
| - `reverseForm(options?: ReverseFormOptions): string` — Return the reversed ip6.arpa form of the address [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L432) | |
| - `isMulticast(): boolean` — Returns true if the given address is a multicast address [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L456) | |
| - `isPrivate(): boolean` — Returns true if the address is in one of the [RFC 1918](https://datatracker.ietf.org/doc/html/rfc1918) private address ranges (`10.0.0.0/8`, `172.16.0.0/12`, `192.168.0.0/16`). [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L464) | |
| - `isLoopback(): boolean` — Returns true if the address is in the loopback range `127.0.0.0/8` ([RFC 1122](https://datatracker.ietf.org/doc/html/rfc1122)). [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L472) | |
| - `isLinkLocal(): boolean` — Returns true if the address is in the link-local range `169.254.0.0/16` ([RFC 3927](https://datatracker.ietf.org/doc/html/rfc3927)). [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L480) | |
| - `isUnspecified(): boolean` — Returns true if the address is the unspecified address `0.0.0.0`. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L488) | |
| - `isBroadcast(): boolean` — Returns true if the address is the limited broadcast address `255.255.255.255` ([RFC 919](https://datatracker.ietf.org/doc/html/rfc919)). [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L496) | |
| - `isCGNAT(): boolean` — Returns true if the address is in the carrier-grade NAT range `100.64.0.0/10` ([RFC 6598](https://datatracker.ietf.org/doc/html/rfc6598)). [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L504) | |
| - `binaryZeroPad(): string` — Returns a zero-padded base-2 string representation of the address [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L512) | |
| - `groupForV6(): string` — Groups an IPv4 address for inclusion at the end of an IPv6 address [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L523) | |
| **Properties** | |
| - `address: string` — [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L14) | |
| - `addressMinusSuffix: string` — [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L15) | |
| - `groups: number` — [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L16) | |
| - `parsedAddress: string[]` — [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L17) | |
| - `parsedSubnet: string` — [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L18) | |
| - `subnet: string` — [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L19) | |
| - `subnetMask: number` — [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L20) | |
| - `v4: boolean` — [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L21) | |
| - `isCorrect: (this: Address4 | Address6) => boolean` — Returns true if the address is correct, false otherwise [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L93) | |
| - `isInSubnet: (this: Address4 | Address6, address: Address4 | Address6) => boolean` — Returns true if the given address is in the subnet of the current address [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv4.ts#L450) | |
| #### Address6 | |
| Represents an IPv6 address | |
| **Constructor** | |
| - `new Address6(address: string, optionalGroups?: number): Address6` | |
| **Static methods** | |
| - `static isValid(address: string): boolean` — Returns true if the given string is a valid IPv6 address (with optional CIDR subnet and zone identifier), false otherwise. Host bits in the subnet portion are allowed (e.g. `2001:db8::1/32` is valid); for strict network-address validation compare `correctForm()` to `startAddress().correctForm()`, or use `networkForm()`. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L163) | |
| - `static fromBigInt(bigInt: bigint): Address6` — Convert a BigInt to a v6 address object. The value must be in the range `[0, 2**128 - 1]`; otherwise `AddressError` is thrown. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L184) | |
| - `static fromURL(url: string): { error: string; address: null; port: null } | { error?: undefined; address: Address6; port: number | null }` — Parse a URL (with optional bracketed host and port) into an address and port. Returns either `{ address, port }` on success or `{ error, address: null, port: null }` if the URL could not be parsed. Ports are returned as numbers (or `null` if absent or out of range). [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L209) | |
| - `static fromAddressAndMask(address: string, mask: string): Address6` — Construct an `Address6` from an address and a hex subnet mask given as separate strings (e.g. as returned by Node's `os.networkInterfaces()`). Throws `AddressError` if the mask is non-contiguous (e.g. `ffff::ffff`). [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L273) | |
| - `static fromAddressAndWildcardMask(address: string, wildcardMask: string): Address6` — Construct an `Address6` from an address and a Cisco-style wildcard mask given as separate strings (e.g. `::ffff:ffff:ffff:ffff` for a `/64`). The wildcard mask is the bitwise inverse of the subnet mask. Throws `AddressError` if the mask is non-contiguous. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L287) | |
| - `static fromWildcard(input: string): Address6` — Construct an `Address6` from a wildcard pattern with trailing `*` groups. The number of trailing wildcards determines the prefix length: each `*` represents 16 bits. `::` is expanded to zero groups (not wildcards) before evaluating trailing wildcards. Only trailing whole-group wildcards are supported. Partial-group wildcards (e.g. `2001:db8::0*`) and interior wildcards (e.g. `*::1`) throw `AddressError`. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L310) | |
| - `static fromAddress4(address: string): Address6` — Create an IPv6-mapped address given an IPv4 address [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L371) | |
| - `static fromArpa(arpaFormAddress: string): Address6` — Return an address from ip6.arpa form [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L387) | |
| - `static fromAddress4Nat64(address: string, prefix: string): Address6` — Embed an IPv4 address into a NAT64 IPv6 address using the encoding defined by [RFC 6052](https://datatracker.ietf.org/doc/html/rfc6052). The default prefix is the well-known prefix `64:ff9b::/96`. The prefix length must be one of 32, 40, 48, 56, 64, or 96; for prefixes shorter than /64 the IPv4 octets are split around the reserved bits 64–71. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L1048) | |
| - `static fromByteArray(bytes: any[]): Address6` — Convert a byte array to an Address6 object. To convert from a Node.js `Buffer`, spread it: `Address6.fromByteArray([...buf])`. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L1154) | |
| - `static fromUnsignedByteArray(bytes: any[]): Address6` — Convert an unsigned byte array to an Address6 object. To convert from a Node.js `Buffer`, spread it: `Address6.fromUnsignedByteArray([...buf])`. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L1164) | |
| **Instance methods** | |
| - `microsoftTranscription(): string` — Return the Microsoft UNC transcription of the address [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L413) | |
| - `mask(mask?: number): string` — Return the first n bits of the address, defaulting to the subnet mask [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L422) | |
| - `possibleSubnets(subnetSize?: number): string` — Return the number of possible subnets of a given size in the address [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L432) | |
| - `startAddress(): Address6` — The first address in the range given by this address' subnet Often referred to as the Network Address. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L457) | |
| - `startAddressExclusive(): Address6` — The first host address in the range given by this address's subnet ie the first address after the Network Address [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L466) | |
| - `endAddress(): Address6` — The last address in the range given by this address' subnet Often referred to as the Broadcast [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L484) | |
| - `endAddressExclusive(): Address6` — The last host address in the range given by this address's subnet ie the last address prior to the Broadcast Address [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L493) | |
| - `subnetMaskAddress(): Address6` — The hex form of the subnet mask, e.g. `ffff:ffff:ffff:ffff::` for a `/64`. Returns an `Address6`; call `.correctForm()` for the string. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L503) | |
| - `wildcardMask(): Address6` — The Cisco-style wildcard mask, e.g. `::ffff:ffff:ffff:ffff` for a `/64`. This is the bitwise inverse of `subnetMaskAddress()`. Returns an `Address6`; call `.correctForm()` for the string. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L515) | |
| - `networkForm(): string` — The network address in CIDR string form, e.g. `2001:db8::/32` for `2001:db8::1/32`. For an address with no explicit subnet the prefix is `/128`, e.g. `networkForm()` on `2001:db8::1` returns `2001:db8::1/128`. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L528) | |
| - `getScope(): string` — Return the scope of the address. The 4-bit scope field ([RFC 4291 §2.7](https://datatracker.ietf.org/doc/html/rfc4291#section-2.7)) is only defined for multicast addresses; for unicast addresses the scope is derived from the address type per [RFC 4007 §6](https://datatracker.ietf.org/doc/html/rfc4007#section-6). [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L540) | |
| - `getType(): string` — Return the type of the address [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L567) | |
| - `getBits(start: number, end: number): bigint` — Return the bits in the given range as a BigInt [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L582) | |
| - `getBitsBase2(start: number, end: number): string` — Return the bits in the given range as a base-2 string [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L590) | |
| - `getBitsBase16(start: number, end: number): string` — Return the bits in the given range as a base-16 string [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L598) | |
| - `getBitsPastSubnet(): string` — Return the bits that are set past the subnet mask length [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L614) | |
| - `reverseForm(options?: ReverseFormOptions): string` — Return the reversed ip6.arpa form of the address [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L624) | |
| - `correctForm(): string` — Returns the address in correct form, per [RFC 5952](https://datatracker.ietf.org/doc/html/rfc5952): leading zeros stripped, the longest run of zero groups collapsed to `::`, and hex digits lowercased (e.g. `2001:db8::1`). This is the recommended form for display. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L659) | |
| - `binaryZeroPad(): string` — Return a zero-padded base-2 string representation of the address [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L721) | |
| - `parse4in6(address: string): string` — Parses a v4-in-v6 string (e.g. `::ffff:192.168.0.1`) by extracting the trailing IPv4 address into `this.address4` / `this.parsedAddress4` and returning the address with the v4 portion converted to two v6 groups. Used internally by `parse()`. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L735) | |
| - `parse(address: string): string[]` — Parses an IPv6 address string into its 8 hexadecimal groups (expanding any `::` elision and any trailing v4-in-v6 portion) and stores the result on `this.parsedAddress`. Called automatically by the constructor; you typically don't need to call it directly. Throws `AddressError` if the input is malformed. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L783) | |
| - `canonicalForm(): string` — Returns the canonical (fully expanded) form of the address: all 8 groups, each padded to 4 hex digits, with no `::` collapsing (e.g. `2001:0db8:0000:0000:0000:0000:0000:0001`). Useful for sorting and byte-exact comparison. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L863) | |
| - `decimal(): string` — Return the decimal form of the address [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L871) | |
| - `bigInt(): bigint` — Return the address as a BigInt [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L879) | |
| - `to4(): Address4` — Return the last two groups of this address as an IPv4 address string. If this address carries a CIDR prefix that covers the trailing 32 bits (i.e. `subnetMask >= 96`), the resulting `Address4` inherits the corresponding v4 prefix (`subnetMask - 96`); otherwise it defaults to `/32`. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L894) | |
| - `to4in6(): string` — Return the v4-in-v6 form of the address [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L916) | |
| - `inspectTeredo(): TeredoProperties` — Decodes the Teredo tunneling fields embedded in this address. Returns the Teredo prefix, server IPv4, client IPv4, raw flag bits, cone-NAT flag, UDP port, and Microsoft-format flag breakdown (reserved, universal/local, group/individual, nonce). Only meaningful for addresses in `2001::/32`. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L937) | |
| - `inspect6to4(): SixToFourProperties` — Decodes the 6to4 tunneling fields embedded in this address. Returns the 6to4 prefix and the embedded IPv4 gateway address. Only meaningful for addresses in `2002::/16`. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L1002) | |
| - `to6to4(): Address6 | null` — Return a v6 6to4 address from a v6 v4inv6 address [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L1022) | |
| - `toAddress4Nat64(prefix: string): Address4 | null` — Extract the embedded IPv4 address from a NAT64 IPv6 address using the encoding defined by [RFC 6052](https://datatracker.ietf.org/doc/html/rfc6052). The default prefix is the well-known prefix `64:ff9b::/96`. Returns `null` if this address is not contained within the given prefix. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L1089) | |
| - `toByteArray(): number[]` — Return a byte array. To get a Node.js `Buffer`, wrap the result: `Buffer.from(address.toByteArray())`. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L1124) | |
| - `toUnsignedByteArray(): number[]` — Return an unsigned byte array. To get a Node.js `Buffer`, wrap the result: `Buffer.from(address.toUnsignedByteArray())`. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L1144) | |
| - `isCanonical(): boolean` — Returns true if the address is in the canonical form, false otherwise [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L1195) | |
| - `isLinkLocal(): boolean` — Returns true if the address is a link local address, false otherwise [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L1203) | |
| - `isMulticast(): boolean` — Returns true if the address is a multicast address, false otherwise [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L1219) | |
| - `is4(): boolean` — Returns true if the address was written in v4-in-v6 dotted-quad notation (e.g. `::ffff:127.0.0.1`), false otherwise. This is a notation-level flag and does not reflect whether the address bits lie in the IPv4-mapped (`::ffff:0:0/96`) subnet — for that, see isMapped4. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L1231) | |
| - `isMapped4(): boolean` — Returns true if the address is an IPv4-mapped IPv6 address in `::ffff:0:0/96` ([RFC 4291 §2.5.5.2](https://datatracker.ietf.org/doc/html/rfc4291#section-2.5.5.2)), false otherwise. Unlike is4, this checks the underlying address bits rather than the textual notation, so `::ffff:127.0.0.1` and `::ffff:7f00:1` both return true. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L1243) | |
| - `isTeredo(): boolean` — Returns true if the address is a Teredo address, false otherwise [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L1251) | |
| - `is6to4(): boolean` — Returns true if the address is a 6to4 address, false otherwise [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L1259) | |
| - `isLoopback(): boolean` — Returns true if the address is a loopback address, false otherwise [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L1267) | |
| - `isULA(): boolean` — Returns true if the address is a Unique Local Address in `fc00::/7` ([RFC 4193](https://datatracker.ietf.org/doc/html/rfc4193)). ULAs are the IPv6 equivalent of IPv4 [RFC 1918](https://datatracker.ietf.org/doc/html/rfc1918) private addresses. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L1275) | |
| - `isUnspecified(): boolean` — Returns true if the address is the unspecified address `::`. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L1283) | |
| - `isDocumentation(): boolean` — Returns true if the address is in the documentation prefix `2001:db8::/32` ([RFC 3849](https://datatracker.ietf.org/doc/html/rfc3849)). [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L1291) | |
| - `href(optionalPort?: string | number): string` — Returns the address as an HTTP URL with the host bracketed, e.g. `http://[2001:db8::1]/`. If `optionalPort` is provided it is appended, e.g. `http://[2001:db8::1]:8080/`. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L1302) | |
| - `link(options?: { className?: string; prefix?: string; v4?: boolean }): string` — Returns an HTML `<a>` element whose `href` encodes the address in a URL hash fragment (default prefix `/#address=`). Useful for linking between pages of an address-inspector UI. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L1320) | |
| - `group(): string` — Groups an address [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L1360) | |
| - `regularExpressionString(this: Address6, substringSearch: boolean): string` — Generate a regular expression string that can be used to find or validate all variations of this address [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L1412) | |
| - `regularExpression(this: Address6, substringSearch: boolean): RegExp` — Generate a regular expression that can be used to find or validate all variations of this address. [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L1466) | |
| **Properties** | |
| - `address4: Address4` — [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L98) | |
| - `address: string` — [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L99) | |
| - `addressMinusSuffix: string` — [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L100) | |
| - `elidedGroups: number` — [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L101) | |
| - `elisionBegin: number` — [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L102) | |
| - `elisionEnd: number` — [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L103) | |
| - `groups: number` — [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L104) | |
| - `parsedAddress4: string` — [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L105) | |
| - `parsedAddress: string[]` — [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L106) | |
| - `parsedSubnet: string` — [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L107) | |
| - `subnet: string` — [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L108) | |
| - `subnetMask: number` — [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L109) | |
| - `v4: boolean` — [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L110) | |
| - `zone: string` — [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L111) | |
| - `isInSubnet: (this: Address4 | Address6, address: Address4 | Address6) => boolean` — Returns true if the given address is in the subnet of the current address [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L1183) | |
| - `isCorrect: (this: Address4 | Address6) => boolean` — Returns true if the address is correct, false otherwise [src](https://github.com/beaugunderson/ip-address/blob/master/src/ipv6.ts#L1189) | |
| <!-- API:END --> | |
| ### Used by | |
| `ip-address` is downloaded ~66 million times per week, mostly via the Node proxy/agent ecosystem. The dependency chain runs through a handful of widely-used packages: | |
| - [**socks**](https://github.com/JoshGlazebrook/socks) (~53M weekly) — SOCKS4/5 client for Node; depends on `ip-address` directly. The single biggest source of downloads. | |
| - [**socks-proxy-agent**](https://github.com/TooTallNate/proxy-agents/tree/main/packages/socks-proxy-agent) (~57M weekly) — `http.Agent` for SOCKS proxies; depends on `socks`. Bundled by virtually every CLI that respects `HTTPS_PROXY`. | |
| - [**npm**](https://github.com/npm/cli) and [**pnpm**](https://github.com/pnpm/pnpm) — both bundle `socks-proxy-agent` through their HTTP fetch stack (`make-fetch-happen` → `@npmcli/agent`), so every Node install on the planet pulls in `ip-address` as a transitive dependency. | |
| - [**Puppeteer**](https://github.com/puppeteer/puppeteer) — `@puppeteer/browsers` uses `proxy-agent` for browser-binary downloads, which routes through `socks-proxy-agent` → `socks` → `ip-address`. | |
| - [**proxy-agent**](https://github.com/TooTallNate/proxy-agents/tree/main/packages/proxy-agent) (~28M weekly) and [**pac-proxy-agent**](https://github.com/TooTallNate/proxy-agents/tree/main/packages/pac-proxy-agent) (~27M weekly) — auto-detecting proxy agents (HTTP/HTTPS/SOCKS/PAC) used widely in scraping, headless-browser, and CI tooling. | |
| - [**cacache**](https://github.com/npm/cacache) (~44M weekly) — npm's content-addressable cache; pulls in the same fetch stack. | |
| Beyond the proxy chain, `ip-address` has been used by Juniper Networks' Contrail, Ably's proxy-protocol implementation, Rackspace's serialization framework, IPFS, and the [SwitchyOmega](https://github.com/FelisCatus/SwitchyOmega) Chrome extension, among many others. | |