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How to store DNS output in a variable in nodejs

How do I store the return value of dns.lookup in a variable? If I store it in an array it shows blank.

Following is the code I'm working on:

    const dns = require('dns');
    class Network
    {
        search(host)
        {
            let options = {
                hints: dns.ADDRCONFIG | dns.V4MAPPED,
                all: true,
                verbatim: true
           }

           let addr = [];
           dns.lookup(host, options, (error, address) =>
               {
                   if(error)
                   {
                       console.log("Could not resolve %s\n", host);
                       console.log(error);
                   }
                   address.forEach(ip => {
                       addr.push({
                           address: ip.address,
                           family: ip.family
                       });
                   });
               });
           console.log(addr);
           return addr;
       }
   }   

   const network = new Network();
   let output = network.search("www.google.com");
   console.log(output);

The output of the code is Blank ie []

Please suggest a rememdy.

Thanks

The last parameter to dns.lookup must be a callback as you have already noticed. The method is asynchronous but this line return addr; is not - addr is returned before getting populated. The method definition of search could be changed to take as second parameter a callback that will be called with the result of dns.lookup . Something like this:

search(host, done) {
...
  dns.lookup(host, options, (err, addresses) => {
    ...
    const finalAddresses = [];
    addresses.forEach((ip) => {
      finalAddresses.push({
        address: ip.address,
        family: ip.family
      });
    });

    done(null, finalAddresses);
  });
}

const network = new Network();
network.search("www.google.com", (err, result) => {
  if (err) {
    return console.log(err);
  }

  console.log(result);
});

I would suggest using the async/await syntax along with the very useful util.promisify function.

This gives us code that is more compact, it will also allow you to write your code in a way that's very similar to synchronous code.

We'll then use some destructuring to pick only the properties in the address object(s) we're interested in.

const dns = require('dns');
const promisify = require('util').promisify;

class Network
{
    async search(host)
    {
        let options = {
            hints: dns.ADDRCONFIG | dns.VMAPPED,
            all: true,
            verbatim: true
        }

        let address = await promisify(dns.lookup)(host, options);       
        return address.map( ({address, family}) => {
            return { address, family };
        });
    }
}   

async function testSearch() {
    const network = new Network();
    let output = await network.search("www.google.com");
    console.log(output);
}

testSearch();

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