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 `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 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 `getInitialProps` is present, Next.js will use its default behavior and render the page on-demand, per-request (meaning Server-Side Rendering).
If `getInitialProps` is absent, 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. Any `query` values will be populated client-side after hydration.
`next build` will emit `.html` files for statically optimized pages. For example, the result for the page `pages/about.js` would be:
```bash
.next/server/static/${BUILD_ID}/about.html
```
And if you add `getInitialProps` to the page, it will then be JavaScript, like so:
```bash
.next/server/static/${BUILD_ID}/about.js
```
In development you'll know if `pages/about.js` is optimized or not thanks to the included [static optimization indicator](/docs/api-reference/next.config.js/static-optimization-indicator.md).
## Caveats
- If you have a [custom `App`](/docs/advanced-features/custom-app.md) with `getInitialProps` then this optimization will be disabled for all pages.
- If you have a [custom `Document`](/docs/advanced-features/custom-document.md) 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.
