What is selective hydration, and how do Suspense boundaries help?

Direct answer

Selective hydration lets React hydrate server-rendered UI in independent pieces so important interactions can become usable before every part of the page has finished loading or hydrating.

Suspense boundaries naturally divide the tree into independent hydration units. React can prioritize the pieces needed for visible or user-interacted content instead of treating the page as one all-or-nothing hydration task.

Server HTML: content can be visible before all client JavaScript is ready.
Priority: React can focus hydration work on areas that matter to the user first.
Architecture: Suspense placement therefore affects both loading UX and hydration granularity.