🐶
Next.js

Next.js getStaticPaths: fallback, revalidate, blocking

By Filip on 10/05/2024

Learn how fallback true, false, and blocking, with and without revalidate, dictate Next.js's server-side rendering and incremental static regeneration behavior for dynamic routes.

Next.js getStaticPaths: fallback, revalidate, blocking

Table of Contents

Introduction

In Next.js, when you're building applications with dynamic routes, understanding getStaticPaths and the fallback key is crucial. getStaticPaths helps define which pages to pre-render during the build process. The fallback key determines how Next.js handles requests for paths that haven't been pre-rendered. Let's explore the different fallback options and their use cases.

Step-by-Step Guide

When building a Next.js application with dynamic routes, you'll use getStaticPaths to specify which paths should be pre-rendered at build time. The fallback key in the object returned by getStaticPaths determines how Next.js handles requests for paths that weren't pre-rendered.

Here's a breakdown of the different fallback options:

1. fallback: false

  • Behavior: Only pre-rendered paths will be served. Any requests for paths not specified in getStaticPaths will result in a 404 error.
  • Use case: Ideal for applications where the list of possible paths is known at build time and unlikely to change frequently.
  • Example:
export async function getStaticPaths() {
  // Fetch data to determine pre-rendered paths
  const products = await fetch('https://api.example.com/products').then(res => res.json());

  // Generate paths based on product IDs
  const paths = products.map(product => ({
    params: { id: product.id.toString() },
  }));

  return { paths, fallback: false };
}

2. fallback: true

  • Behavior:
    • Paths specified in getStaticPaths are pre-rendered at build time.
    • For paths not pre-rendered, Next.js will serve a fallback version of the page on the first request.
    • In the background, Next.js will statically generate the HTML for the requested path.
    • Subsequent requests for the same path will be served the statically generated HTML.
  • Use case: Suitable for applications with a large number of possible paths where pre-rendering all of them at build time is impractical.
  • Example:
export async function getStaticPaths() {
  // Pre-render only a subset of paths
  const paths = [{ params: { id: '1' } }, { params: { id: '2' } }];

  return { paths, fallback: true };
}

3. fallback: 'blocking'

  • Behavior:
    • Paths specified in getStaticPaths are pre-rendered at build time.
    • For paths not pre-rendered, Next.js will block the request until the HTML is statically generated.
    • Once generated, the HTML is served, and subsequent requests for the same path will be served the statically generated HTML.
  • Use case: Provides a smoother user experience compared to fallback: true as users don't see a fallback version of the page.
  • Example:
export async function getStaticPaths() {
  // Pre-render only a subset of paths
  const paths = [{ params: { id: '1' } }, { params: { id: '2' } }];

  return { paths, fallback: 'blocking' };
}

Important Considerations:

  • Search Engine Optimization (SEO): Search engines may not index pages served with fallback: true or fallback: 'blocking' if they encounter the fallback version.
  • Caching: Pages generated with fallback: true or fallback: 'blocking' are cached and served from the cache until the revalidate time specified in getStaticProps expires.
  • App Router: The App Router in Next.js 13 offers a different approach to routing and data fetching, potentially impacting how you use getStaticPaths and fallback.

By understanding the different fallback options and their implications, you can choose the best approach for your Next.js application's specific needs.

Code Example

The code defines three examples of the getStaticPaths function used in Next.js for dynamic routes. The first example fetches product data from an API and generates paths based on product IDs, setting fallback to false, meaning any paths not pre-rendered will result in a 404 error. The second example pre-renders only two paths with IDs '1' and '2', setting fallback to true, allowing Next.js to render pages dynamically on request for paths not pre-rendered. The third example is similar to the second but sets fallback to 'blocking', which makes Next.js server-render pages for paths not pre-rendered, blocking the request until the page is generated.

// Example for fallback: false

export async function getStaticPaths() {
  // Fetch data to determine pre-rendered paths
  const products = await fetch('https://api.example.com/products').then(res => res.json());

  // Generate paths based on product IDs
  const paths = products.map(product => ({
    params: { id: product.id.toString() },
  }));

  return { paths, fallback: false };
}

// Example for fallback: true

export async function getStaticPaths() {
  // Pre-render only a subset of paths
  const paths = [{ params: { id: '1' } }, { params: { id: '2' } }];

  return { paths, fallback: true };
}

// Example for fallback: 'blocking'

export async function getStaticPaths() {
  // Pre-render only a subset of paths
  const paths = [{ params: { id: '1' } }, { params: { id: '2' } }];

  return { paths, fallback: 'blocking' };
}

Additional Notes

* This setting offers the best performance as pages are statically generated at build time.
* It simplifies the development process as you don't need to handle loading states or fallback UI.
* However, it's not suitable for applications where the data or the number of pages changes frequently.
  • fallback: true:
    • Offers a balance between performance and flexibility.
    • It's suitable for applications with a large number of pages where pre-rendering all of them is impractical.
    • The initial request for a non-pre-rendered page might be slower, but subsequent requests will be fast.
  • fallback: 'blocking':
    • Provides the best user experience as users don't see a loading state or fallback UI.
    • It's suitable for applications where SEO is critical, as search engines will see the fully rendered page.
    • However, it can lead to slower initial page loads, especially for pages that haven't been accessed before.

Choosing the right fallback option depends on the specific requirements of your Next.js application, considering factors like the number of pages, frequency of data updates, SEO requirements, and desired user experience.

Summary

fallback Value Behavior Use Case
false Only pre-rendered paths are served. Requests for other paths result in a 404 error. Ideal when the list of possible paths is known at build time and unlikely to change frequently.
true - Pre-rendered paths are served directly. - For other paths, a fallback version is shown on the first request while Next.js generates the HTML in the background. - Subsequent requests for the same path receive the statically generated HTML. Suitable for applications with many possible paths where pre-rendering all at build time is impractical.
'blocking' - Pre-rendered paths are served directly. - For other paths, the request is blocked until Next.js statically generates the HTML. - Once generated, the HTML is served, and subsequent requests receive the statically generated HTML. Provides a smoother user experience than fallback: true as users don't see a fallback version.

Conclusion

Understanding how getStaticPaths and the fallback key work is essential for building dynamic routes in Next.js applications. getStaticPaths determines which pages are pre-rendered at build time, while fallback dictates how Next.js handles requests for paths that weren't pre-rendered. The choice of fallback value (false, true, or 'blocking') depends on your application's specific needs, such as the number of pages, data update frequency, SEO considerations, and desired user experience. Each fallback option offers a different trade-off between performance, flexibility, and user experience. By carefully considering these factors, you can optimize your Next.js application for both performance and user satisfaction.

References

Were You Able to Follow the Instructions?

😍Love it!
😊Yes
😐Meh-gical
😞No
🤮Clickbait

Related posts

Fix ReactNode Type Error in TypeScript

Learn how to resolve the TypeScript error "Type '{}' is not assignable to type 'ReactNode'" in your React projects.

Next.js: `next export` vs `next build` Explained

Discover the key differences between `next export` and `next build` in Next.js, and learn which approach is best suited for your project's needs.

Next.js getServerSideProps: Per-Page Usage Guide

Learn how to effectively use getServerSideProps in Next.js to fetch data on every page request, ensuring dynamic and personalized content for your web application.