MongoNetworkError: failed to connect to server [mongodb:27017] on first connect

I'm taking a beginner docker course (https://www.youtube.com/watch?v=3c-iBn73dDE&t=4384s), which I think is very well done.

As part of the course an app is put together with a node server and js frontend, communicating with with docker containers for mongo db and mongo express for persistence.

The node app can be found at https://gitlab.com/nanuchi/techworld-js-docker-demo-app/-/blob/master/app/server.js . containing:

MongoClient.connect("mongodb://admin:password@mongodb:27017", 
function (err, client) {
if (err) throw err;

var db = client.db('user-account');
userObj['userid'] = 1;

I have the 2 docker containers running on ubuntu 20.04 on a chromebook (screenshot). When I run:

11@penguin:~/techworld-js-docker-demo-app/app$ nodejs server.js 
 app listening on port 3000!

but when I open a browser to localhost:3000 , I get:

(node:2716) DeprecationWarning: current Server Discovery and Monitoring engine is deprecated, and will be removed in a future version. To use the new Server Discover and Monitoring    pass option { useUnifiedTopology: true } to the MongoClient constructor.
/home/11/techworld-js-docker-demo-app/app/node_modules/mongodb/lib/topologies/server.js:240
        throw err;
        ^

MongoNetworkError: failed to connect to server [mongodb:27017] on first connect [MongoNetworkError: getaddrinfo EAI_AGAIN mongodb mongodb:27017]
at Pool.<anonymous> (/home/11/techworld-js-docker-demo-app/app/node_modules/mongodb/lib/core/topologies/server.js:431:11)
at Pool.emit (events.js:198:13)
at createConnection (/home/11/techworld-js-docker-demo-app/app/node_modules/mongodb/lib/core/connection/pool.js:559:14)
at connect (/home/11/techworld-js-docker-demo-app/app/node_modules/mongodb/lib/core/connection/pool.js:973:11)
at makeConnection (/home/11/techworld-js-docker-demo-app/app/node_modules/mongodb/lib/core/connection/connect.js:39:11)
at callback (/home/11/techworld-js-docker-demo-app/app/node_modules/mongodb/lib/core/connection/connect.js:261:5)
at Socket.err (/home/11/techworld-js-docker-demo-app/app/node_modules/mongodb/lib/core/connection/connect.js:286:7)
at Object.onceWrapper (events.js:286:20)
at Socket.emit (events.js:198:13)
at emitErrorNT (internal/streams/destroy.js:91:8)

What am I doing wrong?

from MongoNetworkError: failed to connect to server [mongodb:27017] on first connect