MongoDB unable to wait result - node.js

Question

I cannot make MongoClient.connect to await for the results before going on.
I am trying to pass db from the server.js, where I connect my mongoclient, to my routes/api.js where I do my post requests. But it does not work, I always get:
TypeError: Cannot read property 'collection' of undefined
Here is my routes/api.js:
var db = require("../server");
router.post('/video_url', async (req, res) => {
const cursor = db.collection('movie').findOne({ link: req.body.videoURL }, function (findErr, result) {
if (findErr) throw findErr;
console.log(cursor)
});
server.js:
var db = async function () {
return await MongoClient.connect(MONGODB_URI, function(err, client) {
try {
if(err) throw err;
db = client.db('sub-project');
// Start the application after the database connection is ready
app.listen(PORT, () => console.log(`Server listening on port ${PORT}`));
return db;
}
catch(ex) {
console.log(ex)
}
});
}
module.exports = db;
EDIT:
var dbObject = (async function() {
var connection = await new Promise(function(resolve, reject) {
MongoClient.connect(MONGODB_URI, { useNewUrlParser: true }, function(err, client) {
try {
if (err) throw err;
db = client.db('sub-project');
// Start the application after the database connection is ready
app.listen(PORT, () => console.log(`Server listening on port ${PORT}`));
resolve(db);
} catch (ex) {
console.log(ex)
reject(ex);
}
});
});
return connection;
})();
console.log("TYPEOF DB IN", typeof(dbObject))
console.log("TYPEOF DB.COLLECTION IN", typeof(dbObject.collection))
The both console.log() are undefined... is that normal?

Answer 1

Use this code for your server.js. Your code was not working because your function was not getting called when you are requiring it.
var dbObject;
(function() {
MongoClient.connect(MONGODB_URI, { useNewUrlParser: true }, function(err, client) {
try {
if (err) throw err;
db = client.db('sub-project');
// Start the application after the database connection is ready
app.listen(PORT, () => console.log(`Server listening on port ${PORT}`));
dbObject = db;
} catch (ex) {
console.log(ex);
}
});
})();
setTimeout(function() {
console.log("TYPEOF DB IN", typeof(dbObject))
console.log("TYPEOF DB.COLLECTION IN", typeof(dbObject.collection))
}, 2000);
module.exports = dbObject;