How do you type getStaticProps?

When working with Next.js, typing getStaticProps properly is a common question during interviews, especially if you're expected to write type-safe React applications using TypeScript. Understanding how to type getStaticProps well not only helps you catch bugs early but also improves code readability and maintainability, which are critical in production environments.

Let me walk you through the concept, practical usage, and some nuances you should be aware of when typing getStaticProps.

What is getStaticProps?

getStaticProps is a Next.js data-fetching method used to generate static pages at build time. It fetches data and passes it as props to your page component. This approach is great for pages where data doesn't change often, improving performance and SEO by pre-rendering HTML.

Typing getStaticProps in TypeScript

Next.js provides built-in TypeScript types to help you type getStaticProps correctly. The core type is GetStaticProps, which is a generic type allowing you to specify the shape of the props your page expects.

Here’s a simple example:

import { GetStaticProps } from 'next';

interface Props {
  posts: { id: string; title: string }[];
}

export const getStaticProps: GetStaticProps<Props> = async () => {
  const res = await fetch('https://jsonplaceholder.typicode.com/posts');
  const posts = await res.json();

  return {
    props: {
      posts,
    },
  };
};

const BlogPage = ({ posts }: Props) => {
  return (
    <div>
      {posts.map(post => (
        <div key={post.id}>{post.title}</div>
      ))}
    </div>
  );
};

export default BlogPage;

Here’s what’s going on:

• GetStaticProps<Props> tells TypeScript that the props returned by getStaticProps will match the Props interface.
• This ensures that the props object inside the returned object from getStaticProps matches the expected shape.
• Your page component then receives these props with full type safety.

Why is typing getStaticProps important?

Typing helps catch mismatches between the data you fetch and the props your component expects. For example, if you forget to include a required property or mistype a key, TypeScript will warn you at compile time, preventing runtime errors.

Handling params in getStaticProps

If you’re using dynamic routes with getStaticProps, you often receive params as part of the context. Typing this correctly is crucial for maintainability.

import { GetStaticProps, GetStaticPaths } from 'next';

interface Props {
  post: { id: string; title: string; content: string };
}

interface Params {
  id: string;
}

export const getStaticProps: GetStaticProps<Props, Params> = async (context) => {
  const { id } = context.params!; // Non-null assertion because params exist for dynamic routes

  const res = await fetch(`https://jsonplaceholder.typicode.com/posts/${id}`);
  const post = await res.json();

  return {
    props: {
      post,
    },
  };
};

export const getStaticPaths: GetStaticPaths<Params> = async () => {
  const res = await fetch('https://jsonplaceholder.typicode.com/posts');
  const posts = await res.json();

  const paths = posts.map((post: { id: string }) => ({
    params: { id: post.id },
  }));

  return {
    paths,
    fallback: false,
  };
};

Here, GetStaticProps<Props, Params> tells TypeScript what the expected params are, so you get autocomplete and type safety when accessing context.params.

Common mistakes when typing getStaticProps

• Ignoring params type: Many developers forget to type the params object, which can lead to runtime errors when accessing undefined properties.
• Not handling notFound or redirect cases: getStaticProps can return notFound: true or a redirect object. Your return type should accommodate these cases, or you might get type errors.
• Assuming data shape without validation: Fetching data from external APIs without validating or typing the response can cause mismatches. Use interfaces or type guards to ensure the data matches your expected props.
• Forgetting to mark params as optional when fallback: true: If you use fallback: true in getStaticPaths, params might be undefined during fallback rendering, so your types should reflect that.

Performance and maintainability considerations

Typing getStaticProps properly has a direct impact on maintainability. When your team grows or you revisit code months later, clear types help you understand what data is expected and returned.

From a performance perspective, getStaticProps runs at build time, so the typing itself doesn’t affect runtime performance. However, catching errors early through typing can prevent costly bugs in production.

Security considerations

While typing doesn’t directly impact security, it helps prevent bugs that might expose sensitive data or cause unexpected behavior. For example, if you accidentally include sensitive fields in your props, TypeScript can help you spot those before deployment.

Also, when fetching data in getStaticProps, always sanitize and validate external data, especially if it’s user-generated or from untrusted sources.

Comparison with alternatives: getServerSideProps and getInitialProps

Method	When to use	Typing considerations	Performance impact
getStaticProps	Static generation at build time	Use GetStaticProps<Props, Params> for strong typing	Fast, no runtime overhead
getServerSideProps	Server-side rendering on each request	Use GetServerSideProps<Props, Params> similarly	Slower, runs on every request
getInitialProps	Legacy data fetching, runs on server and client	More complex typing, less recommended	Slower, less optimized

In most modern Next.js apps, getStaticProps is preferred when possible because it enables static optimization, which improves performance and scalability.

Interview tips for getStaticProps typing questions

• Explain the purpose of getStaticProps before jumping into typing.
• Show how to use the GetStaticProps generic type with your props interface.
• Discuss how to type params for dynamic routes and why it matters.
• Mention edge cases like notFound and redirect in the return type.
• Highlight common pitfalls, such as forgetting to handle optional params or mismatched data shapes.
• Give a brief comparison with getServerSideProps to show you understand when to use each.
• If you can, share a real-world example from your experience where proper typing saved time or prevented bugs.

Practical production scenario

In one of my recent projects, we had a blog built with Next.js. We used getStaticProps to fetch posts from a headless CMS. Early on, we didn’t type the props properly, which led to subtle bugs when the CMS schema changed. After introducing strict typing with GetStaticProps, we caught these issues during development instead of in production.

We also typed params for dynamic post pages, which helped frontend engineers avoid runtime errors when accessing URL parameters. This practice improved our developer experience and reduced bug tickets related to data fetching.

Additionally, we handled the notFound case explicitly to serve a 404 page when a post was deleted from the CMS but still linked somewhere. This made the app more resilient and user-friendly.

Summary

Typing getStaticProps is straightforward once you understand the GetStaticProps generic type from Next.js. It’s essential to define your props interface clearly, type dynamic route parameters, and handle special return cases like notFound and redirect. Doing so improves code quality, developer experience, and helps avoid runtime errors.

Remember to validate external data and keep your types in sync with your API responses. This attention to detail pays off in maintainable, scalable Next.js applications.