You really want multiple layers of "server" code, one of which is a tweaked version of what's on the client, and one of which is purely server-side. For exampl

You really want multiple layers of "server" code, one of which is a tweaked version of what's on the client, and one of which is purely server-side. For example, you can't trust client-side code for security/authentication purposes. You almost certainly don't want client code to connect directly to your database and run arbitrary queries/look-ups. So some kind of server-side-only wrapper around your DB, at least, is required. But the reason you'd run "client" code on the server is to have a layer of universal HTML-rendering code. The server needs to do it for fast initial page loads (and SEO), and the client needs to do it for fast, offline page loads. At the same time, there's a bunch of code that will run on the client side only, e.g. click handlers, animations, etc. There's essentially nothing for that code to do on the server, but I think it's still basically correct to call it "universal" when you mean "client code that can also run on the server" which is what Sapper provides.