Undefined response in callback node js?

Question

I am trying to call a function that retrives all the document from a collection and returns the data. Now, everything works fine but for some reason , I am getting an undefined response from my function callback. What could I be doing wrong?

var findImages = function(db, callback) {
    var s ="";
    db.collection('imageinfo', function(err, collection) {
        collection.find().toArray(function(err, items) {

            for(var i=0;i<items.length;i++){
                console.log("imagename",items[i].imagename);
                s =s + items[i].imagename+",";

            }

            if(i==items.length){
                callback(s);

            }
        });


    });



};


app.get("/fetchrecords",function(req,res){
    console.log("entered");
    findImages(db,function(req,res){
     console.log("res",res);
    });

    res.end("Sent records");

});

... function(err, items) { if (err) return callback(err) .... — Aikon Mogwai
– Aikon Mogwai, Commented Oct 19, 2017 at 9:52

gurvinder372 · Accepted Answer · 2017-10-19 09:50:51Z

1

I am getting an undefined response from my function callback.

Callback of findImages only returns one parameter when invoked callback(s);

But in your callback definition you logging second argument. Instead, log only first argument

findImages(db,function(res){
 console.log("res",res);
});

answered Oct 19, 2017 at 9:50

gurvinder372

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H. Hakvoort · Accepted Answer · 2017-10-19 09:55:12Z

0

i will never be the same as items.length. Because reason 1 i is not in your for loop, so it is out of scope. Reason 2, even if i is in your loop, your loop will give i a maximum value of items.length -1 because you use <.

Your solution:

var findImages = function(db, callback) {
    var s ="";
    db.collection('imageinfo', function(err, collection) {
        collection.find().toArray(function(err, items) {
           var i = 0;
            while( i<items.length){
                console.log("imagename",items[i].imagename);
                s =s + items[i].imagename+",";
                i++;
            }
              callback(s);

        });


    });



};

answered Oct 19, 2017 at 9:55

H. Hakvoort

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