Node.js DNS response delayed

Question

I'm just trying to concatenate an array containing domains that are the result of a DNS resolution.

This is my code :

        var ipList = [];
        for(var j=0; j < addressList.length; j++) {
            dns.resolve(addressList[j], function(error, ipRange) {
                if(error !== null) {
                    console.log('The DNS request failed.');
                }
                console.log('--1--');
                console.log(ipRange);
                console.log('--2--');
                ipList.concat(ipRange);
            });
        }

        console.log(ipList);

The result I'm getting is this :

[]
--1--
[ '173.194.35.144',
  '173.194.35.145',
  '173.194.35.146',
  '173.194.35.147',
  '173.194.35.148' ]
--2--

It looks like the DNS resolution response arrives after the concat(), like it was delayed. Which means that ipList is an empty array.

Can anyone help me on this ? Thanks in advance !

Answer 1

resolve is async, so it's not done when you do the final print. Use synchronous DNS (can't find this for node.js immediately), or arrange your callbacks properly.