MongoDB read and stringfiy json

mongodbread.js

var http = require('http');
var mongoose = require('mongoose');

var Schema = mongoose.Schema;

var userSchema = new Schema({ name: String, lastname: String, yas: Number, yer: String });

http.createServer(function (req, res) {
    res.writeHead(200, {'Content-Type': 'application/json; charset=utf-8'});

    mongoose.connect('mongodb://localhost/bookmarks');
    var db = mongoose.connection;
    db.on('error', console.error.bind(console, 'connection error:'));
    db.once('open', function callback () {



        var mUsers = mongoose.model('users', userSchema);

        mUsers.find().lean().exec(function(err,users) {


             sonuc=JSON.stringify(users);

            console.log(sonuc);

            if(req.url==='/index') {

                console.log('Request Url'+req.url);
                res.end(sonuc);
            }
            if(req.url==='/test'){
                console.log('TEST');
            }
           db.close();

        });


    });


}).listen(1337,'127.0.0.1');