Before running scripts as below, you may want to change the port that express listens on in server/app.js and you may want to change the URL that client/app.js sends the request to (you will have to change it if you change the port in server).

In terminal tab 1:

cd server && npm i && node app.js

In terminal tab 2:

cd client && npm i && node app.js

running client/app.js, as above, gives ERR_ABORTED error.