get ip address by domain with dns.lookup() node.js

Question

Referring to this documentation I am getting the ip address from domain name inside console.log the code looks like so:

const dns = require('dns');

dns.lookup('iana.org', (err, address, family) => {
  console.log('address: %j family: IPv%s', address, family);
});

Output of console.log is fine. However I can't get address outside that scope. The return statement of the dns.lookup function is an object.

What I've tried so far:

const ipAddress = dns.lookup("www.aWebSiteName.am", (err, address, family) => {
  if(err) throw err;
  return address;
});

console.log(ipAddress);

I am getting:

GetAddrInfoReqWrap {
  callback: [Function],
  family: 0,
  hostname: 'www.aWebSiteName.am',
  oncomplete: [Function: onlookup] }

Answer 1

You can not because dns.lookup() function is working async.

Though the call to dns.lookup() will be asynchronous from JavaScript's perspective, it is implemented as a synchronous call to getaddrinfo(3) that runs on libuv's threadpool. This can have surprising negative performance implications for some applications, see the UV_THREADPOOL_SIZE documentation for more information.

There are different ways to take the result. Welcome to JS world!

Callback

dns.lookup("www.aWebSiteName.am", (err, address, family) => {
  if(err) throw err;
  printResult(address);
});

function printResult(address){
   console.log(address);
}

Promise

const lookupPromise = new Promise((resolve, reject) => {
    dns.lookup("www.aWebSiteName.am", (err, address, family) => {
        if(err) reject(err);
        resolve(address);
    });
});

lookupPromise().then(res => console.log(res)).catch(err => console.error(err));

Promise async/await

async function lookupPromise(){
    return new Promise((resolve, reject) => {
        dns.lookup("www.aWebSiteName.am", (err, address, family) => {
            if(err) reject(err);
            resolve(address);
        });
   });
};

try{
    cons address = await lookupPromise();
}catch(err){
    console.error(err);
}

Answer 2

This is normal because "dns.lookup" is executed asynchronously

So you can't just use the returned value of the function

You need to do your logic inside the callback or make an helper to promisfy the function and execute it in async function with await.

Something like this:

function lookup(domain) {
  return new Promise((resolve, reject) => {
    dns.lookup(address, (err, address, family) => {
      if (err) {
        reject(err)
      } else {
        resolve({ address, family })
      }
    })
  })
}

async function test() {
  let ipAddress = await lookup(("www.aWebSiteName.am");
}

EDIT:

You can also use:

const dns = require('dns');
dnsPromises = dns.promises;

async function test() {
  let data = await dnsPromises.lookup(("www.aWebSiteName.am");
}