getStaticProps API

If you export an async function called getStaticProps from a page, Blitz will pre-render this page at build time using the props returned by getStaticProps.

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

The context parameter is an object containing the following keys:

• params contains the route parameters for pages using dynamic routes. For example, if the page name is [id].js , then params will look like { id: ... }. To learn more, take a look at the Dynamic Routing documentation. You should use this together with getStaticPaths, which we’ll explain later.

• preview is true if the page is in the preview mode and undefined otherwise. See the Preview Mode documentation.

• previewData contains the preview data set by setPreviewData. See the Preview Mode documentation.

• locale contains the active locale (if enabled).

• locales contains all supported locales (if enabled).

• defaultLocale contains the configured default locale (if enabled).

getStaticProps should return an object with:

• props - A required object with the props that will be received by the page component. It should be a serializable object

• revalidate - An optional amount in seconds after which a page re-generation can occur. More on Incremental Static Regeneration

• notFound - An optional boolean value to allow the page to return a 404 status and page. Below is an example of how it works:

  export async function getStaticProps(context) {
    const res = await fetch(`https://.../data`)
    const data = await res.json()
  
    if (!data) {
      return {
        notFound: true,
      }
    }
  
    return {
      props: {}, // will be passed to the page component as props
    }
  }

  Note: notFound is not needed for fallback: false mode as only paths returned from getStaticPaths will be pre-rendered.

• redirect - An optional redirect value to allow redirecting to internal and external resources. It should match the shape of { destination: string, permanent: boolean }. In some rare cases, you might need to assign a custom status code for older HTTP Clients to properly redirect. In these cases, you can use the statusCode property instead of the permanent property, but not both. Below is an example of how it works:

  export async function getStaticProps(context) {
    const res = await fetch(`https://...`)
    const data = await res.json()
  
    if (!data) {
      return {
        redirect: {
          destination: "/",
          permanent: false,
        },
      }
    }
  
    return {
      props: {}, // will be passed to the page component as props
    }
  }

  Note: Redirecting at build-time is currently not allowed and if the redirects are known at build-time they should be added in blitz.config.js.

Note: You can import modules in top-level scope for use in getStaticProps. Imports used in getStaticProps will not be bundled for the client-side.

This means you can write server-side code directly in getStaticProps. This includes reading from the filesystem or a database.

Note: You should not use fetch() to call an API route in getStaticProps. Instead, directly import the logic used inside your API route. You may need to slightly refactor your code for this approach.

Fetching from an external API is fine!

Simple Example

Example: Your blog page needs to load it's data from your database or from a CMS (content management system).

function Blog({posts}) {
  // Render posts...
}

// This function gets called during pre-rendering
export async function getStaticProps() {
  // 1. Use a Blitz query
  // 2. Directly access your database
  // 3. Or call an external API endpoint to get posts
  const posts = /* ... */

  // By returning { props: posts }, the Blog component
  // will receive `posts` as a prop at build time
  return {
    props: {
      posts,
    },
  }
}

export default Blog

When should I use getStaticProps?

You should use getStaticProps if:

• The data for the page is not private and can be publicly available
• The data comes from headless CMS.
• The data can be publicly cached (not user-specific).
• The page must be pre-rendered (for SEO) and be very fast — getStaticProps generates HTML and JSON files, both of which can be cached by a CDN for performance.

TypeScript: Use GetStaticProps

For TypeScript, you can use the GetStaticProps type from blitz:

import { GetStaticProps } from "blitz"

export const getStaticProps: GetStaticProps = async (context) => {
  // ...
}

If you want to get inferred typings for your props, you can use InferGetStaticPropsType<typeof getStaticProps>, like this:

import { InferGetStaticPropsType } from "blitz"

type Post = {
  author: string
  content: string
}

export const getStaticProps = async () => {
  const res = await fetch("https://.../posts")
  const posts: Post[] = await res.json()

  return {
    props: {
      posts,
    },
  }
}

function Blog({ posts }: InferGetStaticPropsType<typeof getStaticProps>) {
  // will resolve posts to type Post[]
}

export default Blog

Incremental Static Regeneration

With getStaticProps you don't have to stop relying on dynamic content, as static content can also be dynamic. Incremental Static Regeneration allows you to update existing pages by re-rendering them in the background as traffic comes in.

Inspired by stale-while-revalidate, background regeneration ensures traffic is served uninterruptedly, always from static storage, and the newly built page is pushed only after it's done generating.

Consider our previous getStaticProps example, but now with regeneration enabled:

function Blog({ posts }) {
  return (
    <ul>
      {posts.map((post) => (
        <li>{post.title}</li>
      ))}
    </ul>
  )
}

// This function gets called at build time on server-side.
// It may be called again, on a serverless function, if
// revalidation is enabled and a new request comes in
export async function getStaticProps() {
  // 1. Use a Blitz query
  // 2. Directly access your database
  // 3. Or call an external API endpoint to get posts
  const res = await fetch("https://.../posts")
  const posts = await res.json()

  return {
    props: {
      posts,
    },
    // Next.js will attempt to re-generate the page:
    // - When a request comes in
    // - At most once every second
    revalidate: 1, // In seconds
  }
}

export default Blog

Now the list of blog posts will be revalidated once per second; if you add a new blog post it will be available almost immediately, without having to re-build your app or make a new deployment.

This works perfectly with fallback: true. Because now you can have a list of posts that's always up to date with the latest posts, and have a blog post page that generates blog posts on-demand, no matter how many posts you add or update.

Static content at scale

Unlike traditional SSR, Incremental Static Regeneration ensures you retain the benefits of static:

• No spikes in latency. Pages are served consistently fast
• Pages never go offline. If the background page re-generation fails, the old page remains unaltered
• Low database and backend load. Pages are re-computed at most once concurrently

Reading files: Use process.cwd()

Files can be read directly from the filesystem in getStaticProps.

In order to do so you have to get the full path to a file.

Since Blitz compiles your code into a separate directory you can't use __dirname as the path it will return will be different from the pages directory.

Instead you can use process.cwd() which gives you the directory where Blitz is being executed.

import fs from "fs"
import path from "path"

// posts will be populated at build time by getStaticProps()
function Blog({ posts }) {
  return (
    <ul>
      {posts.map((post) => (
        <li>
          <h3>{post.filename}</h3>
          <p>{post.content}</p>
        </li>
      ))}
    </ul>
  )
}

// This function gets called at build time on server-side.
// It won't be called on client-side, so you can even do
// direct database queries. See the "Technical details" section.
export async function getStaticProps() {
  const postsDirectory = path.join(process.cwd(), "posts")
  const filenames = fs.readdirSync(postsDirectory)

  const posts = filenames.map((filename) => {
    const filePath = path.join(postsDirectory, filename)
    const fileContents = fs.readFileSync(filePath, "utf8")

    // Generally you would parse/transform the contents
    // For example you can transform markdown to HTML here

    return {
      filename,
      content: fileContents,
    }
  })
  // By returning { props: posts }, the Blog component
  // will receive `posts` as a prop at build time
  return {
    props: {
      posts,
    },
  }
}

export default Blog

Technical details

Only runs at build time

Because getStaticProps runs at build time, it does not receive data that’s only available during request time, such as query parameters or HTTP headers as it generates static HTML.

Write server-side code directly

Note that getStaticProps runs only on the server-side. It will never be run on the client-side. It won’t even be included in the JS bundle for the browser. That means you can write code such as direct database queries without them being sent to browsers. You should not fetch an API route from getStaticProps — instead, you can write the server-side code directly in getStaticProps.

You can use this tool to verify what Blitz eliminates from the client-side bundle.

Statically Generates both HTML and JSON

When a page with getStaticProps is pre-rendered at build time, in addition to the page HTML file, Blitz generates a JSON file holding the result of running getStaticProps.

This JSON file will be used in client-side routing through <Link> or the Blitz router. When you navigate to a page that’s pre-rendered using getStaticProps, Blitz fetches this JSON file (pre-computed at build time) and uses it as the props for the page component. This means that client-side page transitions will not call getStaticProps as only the exported JSON is used.

Only allowed in a page

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

One of the reasons for this restriction is that React needs to have all the required data before the page is rendered.

Also, you must use export async function getStaticProps() {} — it will not work if you add getStaticProps as a property of the page component.

Runs on every request in development

In development (blitz dev), getStaticProps will be called on every request.

Preview Mode

In some cases, you might want to temporarily bypass Static Generation and render the page at request time instead of build time. For example, you might be using a headless CMS and want to preview drafts before they're published.

This use case is supported by Blitz by the feature called Preview Mode. Learn more on the Preview Mode documentation.