MongoClient.connect is not responding - node.js

Question

I am trying to connect my Node.js (Express) with my MongoDB atlas by following the official tutorial on their website.
Here is my conn.js code below:
const { MongoClient } = require("mongodb");
const Db = process.env.ATLAS_URI;
let _db;
module.exports = {
connectToServer: function (callback) {
MongoClient.connect(
Db,
{ useNewUrlParser: true, useUnifiedTopology: true },
(err, db) => {
console.log('THIS LOG IS NOT DISPLAYED')
if (db) {
_db = db.db("employees");
console.log("Successfully connected to MongoDB");
}
return callback(err);
}
);
},
getDb: function () {
return _db;
},
};
Here is server.js where I am calling connectToServer() function from conn.js
const express = require("express");
const app = express();
const cors = require("cors");
require("dotenv").config({ path: "./config.env" });
const port = process.env.PORT || 5000;
app.use(cors());
app.use(express.json());
app.use(require("./routes/record"));
const dbo = require("./db/conn");
app.listen(port, () => {
// HERE IS WHERE I CALL THE FUNCTION
dbo.connectToServer(err => {
if (err) console.error(err);
});
console.log(`Server is running on port: ${port}`);
});
Note, that I am getting the "Server is running on port: 5000" message, but I am not getting the "Successfully connected to MongoDB" message and I am not getting any errors, too.
P.S. I made my MongoDB network access 0.0.0.0 so that any IP address can access it. And also if I provide the wrong username and password for my ATLAS_URI, I am getting an authentication error.

Answer 1

Connect returns promise you can use like below.
let _db;
const client = new MongoClient(Db, {
useNewUrlParser: true,
useUnifiedTopology: true,
});
module.exports = {
connectToServer: async (callback) => {
await client.connect();
console.log("Connected successfully to server");
_db = client.db(dbName);
console.log("Successfully connected to MongoDB");
},
getDb: function () {
return _db;
},
};
Note: You can change the order If you want, First connect to DB then start the server. It's completely optional depending on the use case.
(async () => {
try {
await dbo.connectToServer();
app.listen(port, async () => {
// HERE IS WHERE I CALL THE FUNCTION
console.log(`Server is running on port: ${port}`);
});
} catch (error) {
console.log(error);
}
})();

Answer 2

Callback Support has been removed from v5 hence the console.log statements in callback function are not getting printed. To make it work you can use promises/async-await.
Due to same reason an error is thrown when authentication is wrong as connect function is running but failing in this case.
Change log for the same. => "Node.js driver v5 drops support for callbacks in favor of a Promise-only API."