placing 1 mongodb query inside express.Router().get() results in 2 requests

Question

When I place a MongoDB query inside router.get() in /routes/index.js like this:

/* GET home page. */
router.get('/', function(req, res, next) {
  console.log('1 rendering index performing a DB query');

  performQuery(query, function(dbData) {
    res.render('./home/index', dbData);
  });
});

I get this console output:

[nodemon] starting `node ./bin/www`
app.use(/, routes)

SERVER  READY on port 3000
SOCKET.IO  client: /#V261JQOrV3aEyu34AAAA CONN
rendering index performing a DB query -------------------------------------------------> 1
GET / 200 744.652 ms - 4054 -----------------------------------------------------------> 1
SOCKET.IO  client: /#V261JQOrV3aEyu34AAAA DISCONN
GET /stylesheets/main.css 304 4.166 ms - -
GET /images/logo-icon-90.png 304 0.514 ms - -
GET /public/js/libs/socket.io/socket.io.js 304 3.888 ms - -
GET /public/js/libs/jquery/jquery-2.1.4.min.js 304 15.758 ms - -
rendering index performing a DB query -------------------------------------------------> 2
GET / 304 363.686 ms - - --------------------------------------------------------------> 2
SOCKET.IO  client: /#w4kVulgNfEfnJJPOAAAB CONN

I checked if there was another error of some sort taking out the MongoDB query and just rendering '/' and then console outputs just one GET request to '/'. The only thing changing between getting 1 or 2 GET request is placing the MongoDB query.

performQuery.js content:

MongoClient.connect(mongoURL + dbName, function(err, db) {

    assert.equal(err, null);

    const cursor = db.collection(collection).aggregate([
            { $match: query.justVars},
            { $group: {
                    _id: {var1: '$somevar', var2: '$anothervar'},
                    takeScore: {$first: '$score'}
                }
            },
            { $sort: {score: -1}},
            { $group: {
                    _id: '$_id.var1',
                    vars2: { $push: {
                        name: '$_id.var2',
                        score: '$takeScore'
                        }
                     },
                    sumScore: { $sum: '$score'}
                }
            },
            { $sort: {sumScore: -1}}
    ]);

    cursor.toArray(function(error, documents) {
      assert.equal(error, null);

      callback(documents);
      db.close();
    });
  });

QUESTION

Why is there 2 GET request to '/' and not just one?

Answer 1

A possible problem is the cursor.toArray . Can you console.log here:

cursor.toArray(function(error, documents) {
  assert.equal(error, null);

  console.log(documents);

  callback(documents);
  db.close();
});

and check how many extra lines do you have in the console?

It seems that you retrieve 2 documents from the database and in this iteration you call 2 times the callback. You have to call the callback ONLY when the iteration will finish.

What is the SOCKET.IO logs? Is it possible that you have open 2 different tabs on the browser and when you restart the application they are trying to connect automatically and that's why it feels like you have 2 GET requests?