The approach you're describing is pretty much how frameworks like React work. I think there are two main reasons why the more lightweight options don't go for t

The approach you're describing is pretty much how frameworks like React work. I think there are two main reasons why the more lightweight options don't go for this: 1. In the React space, you have to write two conversion steps: first you have to convert your app's data to some wire format (JSON objects or something) on the server, then you have to convert the wire format into HTML on the client ("render" the UI). This is more complex than a single step where you just convert the app's data to HTML on the server. 2. For best performance, the server needs to be able to generate HTML and send it to the client on the initial page load. (React calls this "server-side rendering"; its approach to it doesn't really work for lightweight frameworks because it requires you run JavaScript on the server.) Once you have that capability, you might as well use it as much as possible, rather than implementing a separate code path just for JavaScript.