How does middleware work when using a CDN to host the JS bundles? ie what happens when I've already loaded the bundles and am transitioning to a page that has

How does middleware work when using a CDN to host the JS bundles? ie what happens when I've already loaded the bundles and am transitioning to a page that has different middleware requirements? Is it a client-only middleware implementation? (I want this and have implemented a poor man's version in my _app.tsx).