Automatic Static Optimization

Next.js automatically determines that a page is static (can be prerendered) if it has no blocking data requirements. This determination is made by the absence of getServerSideProps and getInitialProps in the page.

This feature allows Next.js to emit hybrid applications that contain both server-rendered and statically generated pages.

Statically generated pages are still reactive: Next.js will hydrate your application client-side to give it full interactivity.

One of the main benefits of this feature is that optimized pages require no server-side computation, and can be instantly streamed to the end-user from multiple CDN locations. The result is an ultra fast loading experience for your users.

How it works

If getServerSideProps or getInitialProps is present in a page, Next.js will switch to render the page on-demand, per-request (meaning Server-Side Rendering).

If the above is not the case, Next.js will statically optimize your page automatically by prerendering the page to static HTML.

During prerendering, the router's query object will be empty since we do not have query information to provide during this phase. After hydration, Next.js will trigger an update to your application to provide the route parameters in the query object.

The cases where the query will be updated after hydration triggering another render are:

  • The page is a dynamic-route.
  • The page has query values in the URL.
  • Rewrites are configured in your next.config.js since these can have parameters that may need to be parsed and provided in the query.

To be able to distinguish if the query is fully updated and ready for use, you can leverage the isReady field on next/router.

Note: Parameters added with dynamic routes to a page that's using getStaticProps will always be available inside the query object.

next build will emit .html files for statically optimized pages. For example, the result for the page pages/about.js would be:

.next/server/pages/about.html

And if you add getServerSideProps to the page, it will then be JavaScript, like so:

.next/server/pages/about.js

Caveats

  • If you have a custom App with getInitialProps then this optimization will be turned off in pages without Static Generation.
  • If you have a custom Document with getInitialProps be sure you check if ctx.req is defined before assuming the page is server-side rendered. ctx.req will be undefined for pages that are prerendered.
  • Avoid using the asPath value on next/router in the rendering tree until the router's isReady field is true. Statically optimized pages only know asPath on the client and not the server, so using it as a prop may lead to mismatch errors. The active-class-name example demonstrates one way to use asPath as a prop.