Node.js dns.resolve() Method

The dns.resolve() method is an inbuilt application programming interface of the dns module which is used to resolve hostname into an array of the resource records.

Syntax:

dns.resolve( hostname, rrtype, callback )

Parameters: This method accept three parameters as mentioned above and described below:

• hostname: This parameter specifies a string which denotes the hostname to be resolved.
• rrtype: It specifies the resource record type. Its default value is ‘A’. The list of records (‘A’, ‘AAAA’, ‘ANY’, ‘CNAME’, ‘MX’, ‘TXT’, ‘NS’, ‘NAPTR’, ‘PTR’, ‘SOA’, ‘SRV’) are described below:
  • A: IPv4 address
  • AAAA: IPv6 address
  • ANY: Any records
  • CNAME: canonical name records
  • MX: mail exchange records
  • NAPTR: name authority pointer records
  • NS: name server records
  • PTR: pointer records
  • SOA: start of authority records
  • SRV: service records
  • TXT: text records
• callback: It specifies a function which to be called after DNS resolution of the hostname.
  • error: It specifies error if generated.
  • records: It’s string or object that signifies the returned record.

Return Value: This method returns error, records through callback function, These data are passed as parameters to the callback function.





Below examples illustrate the use of dns.resolve() Method in Node.js:

Example 1:

// Node.js program to demonstrate the
// dns.resolve() method

// Accessing dns module
const dns = require('dns');

// Set the rrtype for dns.resolve() method
const rrtype="A";

// Calling dns.resolve() method for hostname
// geeksforgeeks.org and print them in
// console as a callback
dns.resolve('geeksforgeeks.org', rrtype, (err, records)
         => console.log('records: %j', records));

Output:

records: ["34.218.62.116"]

Example 2:

// Node.js program to demonstrate the
// dns.resolve() method

// Accessing dns module
const dns = require('dns');

// Set the rrtype for dns.resolve() method
const rrtype="MX";

// Calling dns.resolve() method for hostname
// geeksforgeeks.org and print them in
// console as a callback
dns.resolve('geeksforgeeks.org', rrtype, (err, records)
             => console.log('records: %j', records));

Output:

records: [
    {"exchange":"alt1.aspmx.l.google.com", "priority":5},
    {"exchange":"alt2.aspmx.l.google.com", "priority":5},
    {"exchange":"aspmx.l.google.com", "priority":1},
    {"exchange":"alt3.aspmx.l.google.com", "priority":10},
    {"exchange":"alt4.aspmx.l.google.com", "priority":10}
]

Example 3:

// Node.js program to demonstrate the
// dns.resolve() method

// Accessing dns module
const dns = require('dns');

// Set the rrtype for dns.resolve() method
const rrtype="TXT";

// Calling dns.resolve() method for hostname
// geeksforgeeks.org and print them in
// console as a callback
dns.resolve('geeksforgeeks.org', rrtype, (err,
    records) => console.log('records: %j', records));

Output:

records: [
    ["v=spf1 include:amazonses.com include:_spf.google.com -all"],
    ["fob1m1abcdp777bf2ncvnjm08n"]
]

Example 4:

// Node.js program to demonstrate the
// dns.resolve() method

// Accessing dns module
const dns = require('dns');

// Set the rrtype for dns.resolve() method
const rrtype="NS";

// Calling dns.resolve() method for hostname
// geeksforgeeks.org and print them in
// console as a callback
dns.resolve('geeksforgeeks.org', rrtype, (err,
    records) => console.log('records: %j', records));

Output:

records: [
    "ns-1520.awsdns-62.org", 
    "ns-1569.awsdns-04.co.uk",
    "ns-245.awsdns-30.com",
    "ns-869.awsdns-44.net"
]

Note: The above program will compile and run by using the node index.js command.

Reference: https://nodejs.org/api/dns.html#dns_dns_resolve_hostname_rrtype_callback