MERN Stack Tutorial Error - NOT

I’ve tried doing the How to Use MERN Stack: A Complete Guide but keep getting an error with the server/db/conn.js file on line 13:

_db = db.db("myFirstDatabase");

There error is:

TypeError: Cannot read property 'db' of undefined

Connecting via the Node code generated by Atlas works just fine. Also, I cloned the GitHub repo and get the exact same error. The actual function call is this:

  connectToServer: function (callback) {
      client.connect(function (err, db) {
          _db = db.db("myFirstDatabase");
          return callback(err);
          console.log("Successfully connected to MongoDB.");

But, literally, nothing is getting assigned to the db parameter when called. The Atlas connection code only has one parameter: err.

I’ve tried this on both macOS 11.3.1 and Debion 10.9 and the exact same thing happens. Since it happens on the GitHub code, I know that I’m not the one causing it by accidentally doing something wrong. And, since the Atlas connection code works, I know that the URI is correct.

Please advise on what I need to do to fix this and then please update the website and GitHub with the information as well. Thank you!

Version Numbers:

Node: 14.17.0
Npm: 6.14.13

While this is easy to reproduce and you can get the error info yourself, here it is in all of its glory:

          throw error;

TypeError: Cannot read property 'db' of undefined
at mern-stack-example/mern/server/db/conn.js:14:16
    at mern-stack-example/mern/server/node_modules/mongodb/lib/utils.js:688:9
    at mern-stack-example/mern/server/node_modules/mongodb/lib/mongo_client.js:257:23
    at connectCallback (mern-stack-example/mern/server/node_modules/mongodb/lib/operations/connect.js:365:5)
    at mern-stack-example/mern/server/node_modules/mongodb/lib/operations/connect.js:552:14
    at connectHandler (mern-stack-example/mern/server/node_modules/mongodb/lib/core/sdam/topology.js:286:11)
    at cb (mern-stack-example/mern/server/node_modules/mongodb/lib/core/sdam/topology.js:684:18)
    at mern-stack-example/mern/server/node_modules/mongodb/lib/cmap/connection_pool.js:348:13
    at mern-stack-example/mern/server/node_modules/mongodb/lib/core/sdam/server.js:282:16
    at Object.callback (mern-stack-example/mern/server/node_modules/mongodb/lib/cmap/connection_pool.js:345:7)

Hi @Blaztek,

Welcome to MongoDB community.

I have tested this guide in the past and it worked.

How did you install the MongoDB driver? What is its version?

It might be that you are failing to connect to the Atlas cluster… Have you verified you can access it via a mongo shell connection from the howt you run the tutorial from?


You’re right. The password on Atlas - I typed it wrong, so it wasn’t connecting properly. It works now.

Thank you so much!

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I will look into a better error message on this scenario as you should get an error in that case.

Thanks for highlighting :wink:

Happy coding…

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Hi @Blaztek,

We have fixed the code to have better connection error handling.


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