Setting up reverse-proxy(?) for Node.js with Egoist Webpack and production env?

Not sure this is called reverse-proxy. My frontend is on port 4000 and a Node.js backend is running on port 5000. How do you config Webpack(egoist?) to forward all requests from \server\backend to port 5000's root path? Also, what is the correct way to deploy the project on the production server?

What did I try so far? Looked here but the Egoist doesn't have a webpack.config.js.

And then I looked here which appears to be the solution but I still don't understand why it would work with this setup in production.

via zehelvion