Next.js Caching: unstable_cache vs. React Cache Compared

Caching plays a pivotal role in web application performance, enabling faster responses and reducing server load. Both Next.js and React offer caching mechanisms, but they serve different purposes and are used in different contexts. This article delves into the details of Next.js unstable_cache and React Cache, highlighting their differences, use cases, and examples.

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What is Caching in Next.js?

Caching is the process of storing data temporarily so that future requests for the same data can be served faster. In Next.js, caching is essential for:

• Reducing server load
• Improving page load times
• Enhancing user experience
• Optimizing resource usage

Next.js provides multiple ways to implement caching, and two of the most notable options are unstable_cache and React Cache.

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What is Next.js unstable_cache?

The unstable_cache function in Next.js is an experimental API designed to cache data-fetching results for server components in the Next.js App Router. By caching responses, it optimizes performance and ensures that frequently requested data is quickly accessible.

Key Features of unstable_cache

• Server-side caching: Targets server components and caches data-fetching results.
• Granular control: Allows developers to specify caching behavior using options such as time-to-live (TTL) or tags.
• Optimized for edge environments: Can be leveraged in edge runtimes to improve response times.
• Server-Side Caching: Data is cached on the server, reducing the need to fetch it repeatedly.

Syntax and Usage

import { unstable_cache } from 'next/cache';

const fetchData = async () => {
  const data = await fetch('https://api.example.com/data');
  return data.json();
};

const cachedFetchData = unstable_cache(fetchData, ['cache-key'], {
  revalidate: 60, // Time in seconds
});

export default async function Page() {
  const data = await cachedFetchData();
  return (
    <div>
      <h1>Cached Data</h1>
      <pre>{JSON.stringify(data, null, 2)}</pre>
    </div>
  );
}

Options in unstable_cache

• revalidate: Defines the TTL for the cached data. After the specified time, the cache is invalidated, and the data is refetched.
• tags: Helps group and invalidate related caches.

Example: Using tags for Cache Invalidation

Tags can group related caches together, allowing selective invalidation when needed.

import { unstable_cache } from 'next/cache';

const fetchProducts = async () => {
  const response = await fetch('https://api.example.com/products');
  return response.json();
};

const cachedFetchProducts = unstable_cache(fetchProducts, ['products'], {
  revalidate: 120, // Cache revalidation every 2 minutes
  tags: ['product-cache'],
});

export default async function ProductPage() {
  const products = await cachedFetchProducts();
  return (
    <div>
      <h1>Products</h1>
      <ul>
        {products.map((product) => (
          <li key={product.id}>{product.name}</li>
        ))}
      </ul>
    </div>
  );
}

// Cache invalidation example
import { revalidateTag } from 'next/cache';

export async function invalidateProductCache() {
  await revalidateTag('product-cache');
  console.log('Product cache invalidated');
}

In the example above, the tags option groups caches under the product-cache tag. When the invalidateProductCache function is called, all caches with the product-cache tag are invalidated, ensuring updated data is fetched.

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What is React Cache?

React Cache, part of the React ecosystem, focuses on caching resources fetched within React components. It is used alongside Suspense for data fetching, making it easier to handle loading states and improve user experience.

Key Features of React Cache

• Declarative caching: Designed to cache data-fetching logic working in server components.
• Integration with Suspense: Works seamlessly with Suspense for declarative data fetching.
• Automatic deduplication: Prevents duplicate fetches by sharing cached resources across components.
• Integration with React: React Cache is tightly integrated with React's rendering pipeline, making it a natural choice for React developers.
• Stable API: Unlike unstable_cache, React Cache is a stable and well-documented feature.
• Caching Per-Request: Eact Cache caches data only during the lifecycle of a single server-side render request. When you refresh the page, a new request is sent to the server, and the cache is reset for that new request.

Syntax and Usage

React Cache utilizes the react package’s built-in cache function to cache data-fetching logic declaratively.

import { cache } from 'react';

const fetchUser = cache(async (userId) => {
  const response = await fetch(`https://api.example.com/user/${userId}`);
  return response.json();
});

function User({ userId }) {
  const user = fetchUser(userId);
  return (
    <div>
      <h1>{user.name}</h1>
      <p>{user.email}</p>
    </div>
  );
}

export default function App() {
  return (
    <React.Suspense fallback={<p>Loading...</p>}>
      <User userId="123" />
    </React.Suspense>
  );
}

Advantages of React Cache

• Simplifies component-level data fetching.
• Reduces boilerplate code for managing loading states and errors.
• Encourages declarative UI design.

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Differences Between Next.js unstable_cache and React Cache

Feature	Next.js unstable_cache	React Cache
Integration Scope	Next.js App Router	React ecosystem
Granularity	Request-level caching	Component-level caching
Revalidation	Configurable TTL and Tags	Automatic deduplication
Dependencies	Next.js-specific API	React Suspense (Optional)

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Use Cases for Each Cache

When to Use unstable_cache

• Optimizing server-side rendering (SSR) performance in Next.js applications.
• Reducing redundant API calls and caching responses for server components in the App Router.
• Improving performance for server-rendered content by caching computed data.

When to Use React Cache

• Declaratively fetching and caching data for server components.
• Managing loading states with Suspense for a smoother user experience.
• Preventing duplicate data fetches across React components by reusing cached data.

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Conclusion

Next.js unstable_cache and React Cache cater to different caching needs in modern web applications. While unstable_cache is optimized for server-side scenarios in Next.js, React Cache excels in component-level caching for server-side rendering in React Server Components. Choosing the right caching mechanism depends on the application’s architecture and specific requirements. By understanding their differences and leveraging their strengths, developers can build highly performant and scalable applications.