React 18 includes architectural improvements to React server-side rendering (SSR) performance. This means you can use
Suspense in your React components in streaming SSR mode and React will render content on the server and send updates through HTTP streams.
React Server Components, an experimental feature, is based on streaming. You can read more about Server Components related streaming APIs in
next/streaming. However, this guide focuses on streaming with React 18.
When you use Suspense in a server-rendered page, there is no extra configuration required to use streaming SSR. When deployed, streaming can be utilized through infrastructure like Edge Functions on Vercel (with the Edge Runtime) or with a Node.js server (with the Node.js runtime). AWS Lambda Functions do not currently support streaming responses.
All SSR pages have the ability to render components into streams and the client continues receiving updates from these streams even after the initial SSR response is sent. When any suspended components resolve down the line, they are rendered on the server and streamed to the client. This means applications can start emitting HTML even before all the data is ready, improving your app's loading performance.
As an added bonus, in streaming SSR mode the client will also use selective hydration to prioritize component hydration based on user interactions, further improving performance.
Next.js supports lazy loading external libraries with
import() and React components with
Read more about how to use
Using resource tags (e.g. scripts or stylesheets) in
next/head won't work as intended with streaming, as the loading order and timing of
next/head tags can no longer be guaranteed once you add Suspense boundaries. We suggest moving resource tags to
next/script with the
lazyOnload strategy, or to
_document. For similar reasons, we also suggest migrating
next/script instances with the
beforeInteractive strategy to
Data fetching within
Suspense boundaries is currently only supported on the client side. Server-side data fetching is not supported yet. Read the Layouts RFC for more information about the future of data fetching on the server.
The following solutions are compatible with Next.js streaming:
CSS-in-JS solutions like
emotion are currently not compatible with streaming. For library authors, check out the upgrade guide to learn more.