Your game isn't kept as a zip file on the server. It's unpacked. You can load any file via AJAX, with a relative path.
This is what I use to turn a folder on my machine into a localhost:3000 site: https://www.npmjs.com/package/http-server
This is what I use to turn a folder on my machine into a localhost:3000 site: https://www.npmjs.com/package/http-server