dns.lookup

History

dns.lookup(hostname, options?, callback): void

Attributes

hostname:string

options:integer | Object

family?:integer | string

The record family. Must be 4, 6, or 0. For backward compatibility reasons,'IPv4' and 'IPv6' are interpreted as 4 and 6 respectively. The value 0 indicates that either an IPv4 or IPv6 address is returned. If the value 0 is used with { all: true } (see below), either one of or both IPv4 and IPv6 addresses are returned, depending on the system's DNS resolver. Default: 0.

hints:number

One or more supported getaddrinfo flags. Multiple flags may be passed by bitwise ORing their values.

all?:boolean

When true, the callback returns all resolved addresses in an array. Otherwise, returns a single address. Default: false.

order?:string

When verbatim, the resolved addresses are returned unsorted. When ipv4first, the resolved addresses are sorted by placing IPv4 addresses before IPv6 addresses. When ipv6first, the resolved addresses are sorted by placing IPv6 addresses before IPv4 addresses. Default: verbatim (addresses are not reordered). Default value is configurable using dns.setDefaultResultOrder() or --dns-result-order.

verbatim?:boolean

When true, the callback receives IPv4 and IPv6 addresses in the order the DNS resolver returned them. When false, IPv4 addresses are placed before IPv6 addresses. This option will be deprecated in favor of order. When both are specified, order has higher precedence. New code should only use order. Default: true (addresses are not reordered). Default value is configurable using dns.setDefaultResultOrder() or --dns-result-order.

callback:Function

err:Error

address:string

A string representation of an IPv4 or IPv6 address. Not provided when options.all is true.

family:integer

4 or 6, denoting the family of address, or 0 if the address is not an IPv4 or IPv6 address. 0 is a likely indicator of a bug in the name resolution service used by the operating system. Not provided when options.all is true.

addresses:Object[]

An array of address objects when options.all is true. Each object has the following properties:

address:string

A string representation of an IPv4 or IPv6 address.

family:integer

4 or 6, denoting the family of address.

Resolves a host name (e.g. 'nodejs.org') into the first found A (IPv4) or AAAA (IPv6) record. All option properties are optional. If options is an integer, then it must be 4 or 6 – if options is not provided, then either IPv4 or IPv6 addresses, or both, are returned if found.

With the all option set to true, the arguments for callback change to (err, addresses), with addresses being an array of objects with the properties address and family.

On error, err is an Error object, where err.code is the error code. Keep in mind that err.code will be set to 'ENOTFOUND' not only when the host name does not exist but also when the lookup fails in other ways such as no available file descriptors.

dns.lookup() does not necessarily have anything to do with the DNS protocol. The implementation uses an operating system facility that can associate names with addresses and vice versa. This implementation can have subtle but important consequences on the behavior of any Node.js program. Please take some time to consult the Implementation considerations section before using dns.lookup().

Example usage:

import dns from 'node:dns';
const options = {
  family: 6,
  hints: dns.ADDRCONFIG | dns.V4MAPPED,
};
dns.lookup('example.org', options, (err, address, family) =>
  console.log('address: %j family: IPv%s', address, family));
// address: "2606:2800:21f:cb07:6820:80da:af6b:8b2c" family: IPv6

// When options.all is true, the result will be an Array.
options.all = true;
dns.lookup('example.org', options, (err, addresses) =>
  console.log('addresses: %j', addresses));
// addresses: [{"address":"2606:2800:21f:cb07:6820:80da:af6b:8b2c","family":6}]

JavaScript

const dns = require('node:dns');
const options = {
  family: 6,
  hints: dns.ADDRCONFIG | dns.V4MAPPED,
};
dns.lookup('example.org', options, (err, address, family) =>
  console.log('address: %j family: IPv%s', address, family));
// address: "2606:2800:21f:cb07:6820:80da:af6b:8b2c" family: IPv6

// When options.all is true, the result will be an Array.
options.all = true;
dns.lookup('example.org', options, (err, addresses) =>
  console.log('addresses: %j', addresses));
// addresses: [{"address":"2606:2800:21f:cb07:6820:80da:af6b:8b2c","family":6}]

JavaScript

If this method is invoked as its util.promisify()ed version, and all is not set to true, it returns a Promise for an Object with address and family properties.

Supported getaddrinfo flags

History

The following flags can be passed as hints to dns.lookup().

dns.ADDRCONFIG: Limits returned address types to the types of non-loopback addresses configured on the system. For example, IPv4 addresses are only returned if the current system has at least one IPv4 address configured.
dns.V4MAPPED: If the IPv6 family was specified, but no IPv6 addresses were found, then return IPv4 mapped IPv6 addresses. It is not supported on some operating systems (e.g. FreeBSD 10.1).
dns.ALL: If dns.V4MAPPED is specified, return resolved IPv6 addresses as well as IPv4 mapped IPv6 addresses.