NodeJS - Main file not receiving return of a lookupService inside a function

Question

So I have a file called 'myinternet_utils.js' and the following function:

exports.hasInternet = function () {

 require('dns').lookupService('8.8.8.8', 53, function (err, hostname, service) {
  return hostname;
 });

};

I also have a file called 'server.js', where I have this piece of code:

var ieUtils_ = require('./myinternet_utils.js');

console.log( ieUtils_.hasInternet() );

The 'console.log' prints 'undefined'.

Why am I not getting the output of the function hasInternet?

Possible duplicate of [How do I return the response from an asynchronous call?](https://stackoverflow.com/questions/14220321/how-do-i-return-the-response-from-an-asynchronous-call) — tkausl, Feb 28 '19 at 10:47

score 0 · Accepted Answer · answered Feb 28 '19 at 10:58

0

It seems like the function you are using is asynchronous. Also your function does not actually return anything, so even if it was synchronous you would still get undefined. Try this instead, using promises:

exports.hasInternet = function () {

    return new Promise(function(resolve, reject) {
        require('dns').lookupService('8.8.8.8', 53, function (err, hostname, service) {
            if(err){
                return reject(err);
            }
            resolve(hostname);
        });
    });

};

and in the main file

var ieUtils_ = require('./myinternet_utils.js');

ieUtils_.hasInternet().then(function(result){
    console.log(result);
})

answered Feb 28 '19 at 10:58

Haris Bouchlis

2,366
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Ok, I'm going to give it a try using your suggestion. However, for the record, the function lookupService actually returns 'hostname'. See: https://nodejs.org/api/dns.html#dns_dns_lookupservice_address_port_callback – Fabricio Ganzert Feb 28 '19 at 12:23
Thank you mr Bouchlis, the Promise works like a charm =) You are a life saver, sir. – Fabricio Ganzert Feb 28 '19 at 12:39
Glad to be of assistance @FabricioGanzert – Haris Bouchlis Feb 28 '19 at 12:57

NodeJS - Main file not receiving return of a lookupService inside a function

1 Answers1