dns.lookup()

dns.lookup(hostname[, options], callback)

Resolves a hostname (e.g. 'nodejs.org') into the first found A (IPv4) or AAAA (IPv6) record. options can be an object or integer. If options is not provided, then IPv4 and IPv6 addresses are both valid. If options is an integer, then it must be 4 or 6.

Alternatively, options can be an object containing these properties:

• family {Number} - The record family. If present, must be the integer 4 or 6. If not provided, both IP v4 and v6 addresses are accepted.
• hints: {Number} - If present, it should be one or more of the supported getaddrinfo flags. If hints is not provided, then no flags are passed to getaddrinfo. Multiple flags can be passed through hints by logically ORing their values. See supported getaddrinfo flags for more information on supported flags.
• all: {Boolean} - When true, the callback returns all resolved addresses in an array, otherwise returns a single address. Defaults to false.

All properties are optional. An example usage of options is shown below.

{
  family: 4,
  hints: dns.ADDRCONFIG | dns.V4MAPPED,
  all: false
}

The callback function has arguments (err, address, family). address is a string representation of an IPv4 or IPv6 address. family is either the integer 4 or 6 and denotes the family of address (not necessarily the value initially passed to lookup).

With the all option set to true, the arguments 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 'ENOENT' not only when the hostname 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().