1. HTML is used to immediately show a fast non-interactive preview of the route to the user. 2. RSC Payload is used to reconcile the Client and Server Component trees. 3. JavaScript is used to hydrate Client Components and make the application interactive.
To hydrate your app, React will “attach” your components’ logic to the initial generated HTML from the server. Hydration turns the initial HTML snapshot from the server into a fully interactive app that runs in the browser.