Array is empty in the response even after pushing elements to it

I am creating backend APIs for a Twitter clone. The below API shows the profile of a user. I want to show the tweets of the people that this user is following. But in my response the tweets array is returning an empty array even though I have pushed the data into this array.

Can somebody help me understand why is the tweets array empty in the response?

app.get('/api/profile', auth, function (req, res) {


    var email1 = req.user.email;
    var followers_data = [];
    var tweets = [];

    follower.find({ emailoffollowee: email1 }, (err, results) => {
        if (err)
            console.log(err);
        else {
            results.map((d, k) => {
                followers_data.push(d.emailoffollower);
            })
            for (var i = 0; i < followers_data.length; i++) {
                Tweet.find({ author: followers_data[i] }, (err, results1) => {
                    if (err)
                        console.log(err);
                    else {
                        results1.map((d, k) => {
                            tweets.push(d);
                        })
                    }
                })
            }
            res.json({
                isAuth: true,
                id: req.user._id,
                email: req.user.email,
                name: req.user.firstname + req.user.lastname,
                followers: followers_data,
                tweet: tweets

            });
        }
    })
        .catch(error => {
            console.log(error);
        })
});```

Answer

You Have Tweet.find() which is an asynchronous function, to resolve the problem I used async/await

app.get('/api/profile', auth, function (req, res) {


var email1 = req.user.email;
var followers_data = [];
var tweets = [];

follower.find({ emailoffollowee: email1 }, async (err, results) => {
    if (err)
        console.log(err);
    else {
        results.map((d, k) => {
            followers_data.push(d.emailoffollower);
        })
        for (var i = 0; i < followers_data.length; i++) {
          let results1 = await Tweet.find({ author: followers_data[i] });
                results1.map((d, k) => {
                    tweets.push(d);
                })
        }
        res.json({
            isAuth: true,
            id: req.user._id,
            email: req.user.email,
            name: req.user.firstname + req.user.lastname,
            followers: followers_data,
            tweet: tweets

        });
    }
})
    .catch(error => {
        console.log(error);
    })
});

I recommend you to read this article async/await