DanSalviano/vanilla-js-spa ? reverse-engineered prompt

Build me a simple single page app with plain JavaScript and a small Express server.

I want it to run locally on port 3001 and open in the browser at localhost:3001. The app should feel like a basic SPA, so navigation and page changes happen without full page reloads. Keep the frontend in a clean, easy to understand structure and make it work with a simple Node server setup.

Please make it easy to install and run, with clear scripts for starting the server and development. If anything about the setup is outdated, feel free to update it, and look up current docs online if you need to. I mostly want a working starter project that I can clone, install, and run right away.

Keep the design simple, but make sure the app is polished enough that it looks like a real example project, not just a blank page.