Nodejs how to access Callback results outsite without setTimeouts?

Question

I am new to nodejs and javascript. I am learning async programming. I am trying to find ip address for a domain name. I am using nodejs inbuild "DNS" library.

dns.resolve(domainName, function onLookup(err, addresses, family) {
            if (err){
                res.send(err);
            } else {
                 console.log(addresses);
                 var domainAddress = addresses;
            }
        });

This is the actual code. I am trying to get the domainAddress out of the call back. Since its async programming, it takes time to get the domainAddress and i am unable to access it for some time.

If i am using a code something like this, i am able to access the domainAddress

dns.resolve(domainName, function onLookup(err, addresses, family) {
                                if (err){
                                    res.send(err);
                                } else {
                                    domainAddress = addresses;
                                }
                            });

        setTimeout(function() {
          console.log(domainAddress);
        }, 1000);

But this i do not feel this is the right way to export a result from callback to the main program.

Can you please give any alternate solution for this problem ?

NOTE: I want to do additional task once i get the IP. I want to find the geo location based on the ip address. For that i need to pass this IP to a separate module called Geoip-lite. But since i am unable to get the address outside its getting very difficult

You can't all the operations that depends on `domainAddress` should be placed within the callback — Arun P Johny, Aug 26 '15 at 09:09
Don't use setTimeout, you don't know how many time is necessary... — Thierry, Aug 26 '15 at 09:10
Wrap you dns.resolve call in a function with a callback as parameter. Call that callback with the domainAdress — cviejo, Aug 26 '15 at 09:11
just look inside a function that uses callbacks and you might understand the concept more clearly — Max Bumaye, Aug 26 '15 at 09:13
@Bala take a look at BlackMamba's answer below. It's doing exactly that — cviejo, Aug 26 '15 at 10:32
I want to do additional task once i get the IP. I want to find the geo location based on the ip address. For that i need to pass this IP to a separate module called Geoip-lite. But since i am unable to get the address outside its getting very difficult — Bala, Aug 26 '15 at 10:45

BlackMamba · Accepted Answer · 2015-08-26T09:14:43.110

2

function myResolve(domainName, callback){
    dns.resolve(domainName, function onLookup(err, addresses, family) {
            if (err){
                return callback(err);
            } else {
                return callback(null, addresses);
            }
        });
}


myResolve(domainName, function(err, addresses){
    if(err){
        return res.send(err);
    } else {
        return res.send(addresses);
    }
});

Please try this code.

edited Aug 26 '15 at 09:14

answered Aug 26 '15 at 09:10

BlackMamba

10,054
7
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1

Could you explain what you've done? It's clearer if there is an explanation. – kemicofa ghost Aug 26 '15 at 09:12
1

Don't rush too much to give answers. The `setTimeout` can be removed here. – Sylvain B Aug 26 '15 at 09:14
This code is not working. I do not want to send the response after this function. I want to do more after getting the ip address. So i want to export the address to the main function. – Bala Aug 26 '15 at 10:27
Now i understand how this works. Thanks for your answer. – Bala Aug 26 '15 at 11:16

score 2 · Answer 2 · answered Aug 26 '15 at 09:11

2

try node.js async module. you can use async series for this.

 var domainAddress;
function findDNS(callback){
   dns.resolve(domainName, function onLookup(err, addresses, family) {
        if (err){
            res.send(err);
        } else {
             console.log(addresses);
              domainAddress = addresses;
              callback(null,"Address found")    
        }
    });
}
function doWhatever(callback){
   console.log("DNS:"+domainAddress);
   callback(null,"OK");
}
async.series([findDNS,doWhatever],function (err, results){
    console.log(results);

});

answered Aug 26 '15 at 09:11

Subham

1,414
4
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async series works and i think i can chain all my events to the array. – Bala Aug 26 '15 at 10:35
you can add more events in this array – Subham Aug 26 '15 at 12:21

Nodejs how to access Callback results outsite without setTimeouts?

2 Answers2