NodeJS Async: Callback already called?

Question

I'm using Async module in Node.JS to keep track of my asynchronous calls. However, I'm getting an error - "Callback already called." Can someone help me out here?

async.each(data['results'], function(result, done) { 
    if (result['twitter_id'] !== null) { //Isolate twitter handle
        var param = { "user.screen_name": result['twitter_id']}
        db.test4.find( param, function(err, users) {
            if( err ) {
                return done(err);
            } else if (!users) {
                res.send("No user found");
            } else {
                users.forEach( function(Result) { 
                    twitter_ids.push(Result);
                    //console.log(Result);
                    done();
                });
            }
        });
    }
}, function(err) {  
    if (err) {
        throw err
    }
    res.send(twitter_ids);
});

you're calling done() in each iteration of the forEach loop. you should move done outside of that loop and it'll work. you should also make sure done() gets called in the "else if" branch too. — aembke
– aembke, Commented Jun 27, 2014 at 22:43
I have never used the Async module, but just looking at your code, it looks like you are firing done() (i.e. your callback) multiple times in the loop — Steve
– Steve, Commented Jun 27, 2014 at 22:43

generalhenry · Accepted Answer · 2014-06-27 22:49:46Z

12

You're calling res.send("No user found"); each time you fail to load. However you can fail to load multiple times.

The solution is to put all your response code in the final callback, not in the each callback.

async.each(data['results'], function(result, done) { 
    if (result['twitter_id'] !== null) { //Isolate twitter handle
        var param = { "user.screen_name": result['twitter_id']}
        db.test4.find( param, function(err, users) {
            if( err ) {
                done(err);
            } else if (!users) {
                done(new Error("No user found"));
            } else {
                users.forEach( function(Result) { 
                    twitter_ids.push(Result);
                    //console.log(Result);
                });
                done();
            }
        });
    } else {
      done();
    }
}, function(err) {  
    if (err) {
        return next(err);
    }
    res.send(twitter_ids);
});

edited Jun 27, 2014 at 22:49

answered Jun 27, 2014 at 22:43

generalhenry

17.3k4 gold badges51 silver badges63 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Steve Over a year ago

While I agree that this is also an issue, I believe the error ("Callback already called.") comes from looping over done() in the else. The OP probably doesn't want to execute the callback (done) multiple times.

generalhenry Over a year ago

ahh you're right. It's both, but that's the one that looks like it throw the error, fixing now.

techalicious Over a year ago

Yeah, didn't catch that haha. Thanks y'all! :)

JayminLimbachiya Over a year ago

You should send return at last instead of sending in each condition

Collectives™ on Stack Overflow

NodeJS Async: Callback already called?

1 Answer 1

4 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related