node-mongodb-native node.js client hangs when MongoClient.connect(...), but mongodb-client (shell mand line) works on terminal. Any clues?

var MongoClient = require('mongodb').MongoClient;

MongoClient.connect(
    'mongodb://my.mongo.db.server.ip:27017/test',
     function(err, db) {

        if(err) throw err;
        console.log("shows during connect call back");

        });

// When load into node shell, it hangs forever

node-mongodb-native node.js client hangs when MongoClient.connect(...), but mongodb-client (shell mand line) works on terminal. Any clues?

var MongoClient = require('mongodb').MongoClient;

MongoClient.connect(
    'mongodb://my.mongo.db.server.ip:27017/test',
     function(err, db) {

        if(err) throw err;
        console.log("shows during connect call back");

        });

// When load into node shell, it hangs forever

• javascript
• node.js
• mongodb

• 1 use the mongoose nodejs client. Works like charm. – V31 Commented Feb 18, 2014 at 8:59
• Thank you, but supposedly mongoose get ODM. Isn't it a little overkill? – Andrew_1510 Commented Feb 18, 2014 at 10:21
• I would not consider it as an overkill because of the benefits it provides like structered data, having definite models to your data etc. With all these features it maintains the flexibility that MongoDb has to offer us. – V31 Commented Feb 18, 2014 at 10:29
• 3 Well I would suggest mongojs library which is more like thin wrapper on native driver. This does not force you do use the predefined structures which what NoSQL tries to avoid. – Risto Novik Commented Feb 18, 2014 at 11:32
• just tried mongojs and mongoose, mongojs works as mongodb itself, nice interface. – Andrew_1510 Commented Feb 18, 2014 at 14:18

2 Answers 2

It's been a long time since this question has been asked, but I'll post an answer for those wishing to use mongodb as opposed to mongoose or mongojs (at the time of this writing mongojs depends on an older insecure version of the mongodb driver).

TL;DR Version

The program executes normally, but adding the line db.close(); will allow your program to terminate normally:

var MongoClient = require('mongodb').MongoClient;

MongoClient.connect(
    'mongodb://my.mongo.db.server.ip:27017/test',
     function(err, db) {
        if(err) throw err;
        console.log("shows during connect call back");
        db.close(); //call this when you are done.
        });

Why Node Appears to Hang When Using mongodb.connect()

As explained in this answer, node will not exit when it has a callback waiting for an event.

In this case, connect() registers a callback that waits for the event 'close' to be emitted, indicating that all database connections have been closed. This is why unless you call db.close(), your script will appear to hang. Note however, everything you code will execute, your program will just not terminate normally.

An Example

To demonstrate, if you put the following code block into a file called connect.js...

const MongoClient = require('mongodb').MongoClient;
async function dbconnect() {
console.log("This will print.");

const db = await MongoClient.connect(
    'mongodb://my.mongo.db.server.ip:27017/test');

console.log("This will print too!");

And execute it within a terminal...

$ node connect.js

the result will be:

$ node connect.js
This will print.
This will print too!

You will get no further mand line prompts.

In conclusion remember to close your database connections, and all will be well in the world!

For anyone else facing a similar issue, all I had to do was add a .catch and it worked fine from there on:

const mongodb = require("mongodb");

const connectDb = mongodb.MongoClient.connect(process.env.MONGO_URI, {
    useNewUrlParser: true,
    useUnifiedTopology: true
}).catch(err =>
    res.status(400).json({ msg: `Could not connect to MongoDB`, err })
);

module.exports = connectDb;