If you export a function called getServerSideProps (Server-Side Rendering) from a page, Next.js will pre-render this page on each request using the data returned by getServerSideProps.

export async function getServerSideProps(context) {
  return {
    props: {}, // will be passed to the page component as props
  }
}

getServerSideProps only runs on server-side and never runs on the browser. If a page uses getServerSideProps, then:

• When you request this page directly, getServerSideProps runs at request time, and this page will be pre-rendered with the returned props
• When you request this page on client-side page transitions through next/link or next/router, Next.js sends an API request to the server, which runs getServerSideProps.

It then returns JSON that contains the result of running getServerSideProps, that JSON will be used to render the page. All this work will be handled automatically by Next.js, so you don’t need to do anything extra as long as you have getServerSideProps defined.

You can use the next-code-elimination tool to verify what Next.js eliminates from the client-side bundle.

getServerSideProps can only be exported from a page. You can’t export it from non-page files.

Note that you must export getServerSideProps as a standalone function — it will not work if you add getServerSideProps as a property of the page component.

The getServerSideProps API reference covers all parameters and props that can be used with getServerSideProps.

You should use getServerSideProps only if you need to pre-render a page whose data must be fetched at request time. Time to First Byte (TTFB) will be higher than getStaticProps because the server must compute the result on every request, and the result can only be cached by a CDN using cache-control headers (which could require extra configuration).

If you do not need to pre-render the data, then you should consider fetching data on the client side.

It can be tempting to reach for an API Route when you want to fetch data from the server, then call that API route from getServerSideProps. This is an unnecessary and inefficient approach, as it will cause an extra request to be made due to both getServerSideProps and API Routes running on the server.

Take the following example. An API route is used to fetch some data from a CMS. That API route is then called directly from getServerSideProps. This produces an additional call, reducing performance. Instead, directly import the logic used inside your API Route into getServerSideProps. This could mean calling a CMS, database, or other API directly from inside getServerSideProps.

If your page contains frequently updating data, and you don’t need to pre-render the data, you can fetch the data on the client side. An example of this is user-specific data:

• First, immediately show the page without data. Parts of the page can be pre-rendered using Static Generation. You can show loading states for missing data.
• Then, fetch the data on the client side and display it when ready.

This approach works well for user dashboard pages, for example. Because a dashboard is a private, user-specific page, SEO is not relevant and the page doesn’t need to be pre-rendered. The data is frequently updated, which requires request-time data fetching.

The following example shows how to fetch data at request time and pre-render the result.