getStaticProps API

info

getStaticProps should only be used for pages that do not require authentication. The statically generated pages will be publicly available via your server and via a CDN if you have one. Therefore they cannot contain any personal or sensitive data.

Also, this is why there is no req and res objects for getStaticProps, because the pages are generated at build time, not at runtime. And at build time, there is no user http request to handle.

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

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, as explained below.

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 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

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 next/router (documentation). 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 start), 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.

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