Fancy JavaScript has nothing to do with serving static content. JavaScript itself is (or should be) static content anyway.

If you're talking about using JS to load content on page load, for whatever reason, that async content can also be static. For example some sites use the URL fragment (hash parameter) to load content, but the server does not receive this:

The fragment identifier functions differently to the rest of the URI: its processing is exclusively client-sided with no participation from the web server - https://en.wikipedia.org/wiki/URI_fragment