getStaticPaths

If a page has Dynamic Routes and uses getStaticProps, it needs to define a list of paths to be statically generated.

When you export a function called getStaticPaths (Static Site Generation) from a page that uses dynamic routes, Next.js will statically pre-render all the paths specified by getStaticPaths.

// pages/posts/[id].js

// Generates `/posts/1` and `/posts/2`
export async function getStaticPaths() {
  return {
    paths: [{ params: { id: '1' } }, { params: { id: '2' } }],
    fallback: false, // can also be true or 'blocking'
  }
}

// `getStaticPaths` requires using `getStaticProps`
export async function getStaticProps(context) {
  return {
    // Passed to the page component as props
    props: { post: {} },
  }
}

export default function Post({ post }) {
  // Render post...
}

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

When should I use getStaticPaths?

You should use getStaticPaths if you’re statically pre-rendering pages that use dynamic routes and:

• The data comes from a headless CMS
• The data comes from a database
• The data comes from the filesystem
• 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

When does getStaticPaths run

getStaticPaths will only run during build in production, it will not be called during runtime. You can validate code written inside getStaticPaths is removed from the client-side bundle with this tool.

How does getStaticProps run with regards to getStaticPaths

• getStaticProps runs during next build for any paths returned during build
• getStaticProps runs in the background when using fallback: true
• getStaticProps is called before initial render when using fallback: blocking

Where can I use getStaticPaths

• getStaticPaths must be used with getStaticProps
• You cannot use getStaticPaths with getServerSideProps
• You can export getStaticPaths from a Dynamic Route that also uses getStaticProps
• You cannot export getStaticPaths from non-page file (e.g. your components folder)
• You must export getStaticPaths as a standalone function, and not a property of the page component

Runs on every request in development

In development (next dev), getStaticPaths will be called on every request.

Generating paths on-demand

getStaticPaths allows you to control which pages are generated during the build instead of on-demand with fallback. Generating more pages during a build will cause slower builds.

You can defer generating all pages on-demand by returning an empty array for paths. This can be especially helpful when deploying your Next.js application to multiple environments. For example, you can have faster builds by generating all pages on-demand for previews (but not production builds). This is helpful for sites with hundreds/thousands of static pages.

// pages/posts/[id].js

export async function getStaticPaths() {
  // When this is true (in preview environments) don't
  // prerender any static pages
  // (faster builds, but slower initial page load)
  if (process.env.SKIP_BUILD_STATIC_GENERATION) {
    return {
      paths: [],
      fallback: 'blocking',
    }
  }

  // Call an external API endpoint to get posts
  const res = await fetch('https://.../posts')
  const posts = await res.json()

  // Get the paths we want to prerender based on posts
  // In production environments, prerender all pages
  // (slower builds, but faster initial page load)
  const paths = posts.map((post) => ({
    params: { id: post.id },
  }))

  // { fallback: false } means other routes should 404
  return { paths, fallback: false }
}

Related

For more information on what to do next, we recommend the following sections: