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);
});

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);
});

• javascript
• node.js
• asynchronous

• 1 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 Commented Jun 27, 2014 at 22:43
• 1 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 Commented Jun 27, 2014 at 22:43

1 Answer 1

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);
});