How to run a server on two ports for the same domain at the same time?

Question

JavaScript

Good day to all.
I have one application folder in which there are two more folders:
- backend - server.js
- frontned - main.ts
So it turns out that through the running server.js I get API === localhost:8080
and on the torus I run the application via webpack-dev-server === localhost:9090
How can I run two ports on the same domain? in digital ocean on the server side I can't figure it out