Next.js 15 Simplifies Caching with Dynamic IO

Caching is a notoriously difficult problem in computer science, and Next.js has often been at the forefront of these challenges. With the release of Next.js 15, Vercel has overhauled the caching system, aiming for a more intuitive and powerful approach. This video explores the new Dynamic IO API, designed to simplify caching and make it more explicit.

The Challenge of Caching in Next.js

Previously, Next.js cached almost everything by default, including server components and fetch calls. While this aimed to optimize performance, it often led to confusion and issues when developers needed to revalidate specific data or opt out of caching. Methods like cache: 'nostore', export const dynamic = 'forcedynamic', and manual cache control headers were cumbersome and prone to errors.

Introducing Dynamic IO in Next.js 15

Next.js 15 introduces Dynamic IO, a new API that provides a more intuitive way to control caching on a granular level. It allows you to cache or not cache anything, simplifying your code and making your caching intentions clearer.

Enabling Dynamic IO (Experimental)

To use Dynamic IO, you need to enable it in your next.config.js file:

module.exports = {
 experimental: {
 dynamicIO: true,
 },
}

You may also need to be on the Next.js canary version using:

npm install next@canary

The video demonstrates the feature using Deno, though Node.js is perfectly acceptable.

Practical Example: Product Description and Price

Let's consider an application that displays a product description and price. The video uses Faker.js to generate fake data, which helps visually demonstrate whether data is cached or not.

Initial State: No Caching

Initially, the page is not cached, resulting in a new product description and price every time the page is refreshed. This happens when the component fetches the data during the request.

Simulating Database Latency

To make the example more realistic, the video introduces a 1second delay to simulate database latency using a delay function in Deno. The data fetching functions are also made asynchronous.

Handling the Error: Caching or Dynamic Rendering

When data fetching is async without specific caching strategies, Next.js requires you to either cache/prerender the page or explicitly make it dynamic using a suspense boundary. The video initially addresses the second point.

Dynamic Rendering with Suspense

The video demonstrates wrapping the page in a suspense boundary using a loading.js file (a Next.js convention). This approach clears the error and ensures fresh data on every request.

Caching with use cache

To cache the data, the video introduces the use cache directive at the top of the page. This is a Next.js specific feature.

"use client";

import { useCache } from 'next/cache'

export default async function Page() {
 useCache();
 // ... rest of your component
}

This caches the data after the first render. Subsequent refreshes display the same cached data until the cache expires.

Cache Expiration and Customization

By default, Next.js uses an infinite cache that's revalidated every 15 minutes. The cacheLife function allows you to modify the cache expiration behavior. You can import this function from `next/cache`.

import { cacheLife } from 'next/cache';

use cache(() => {
 cacheLife('1 day');
});

Custom values can be configured in next.config.js.

Invalidating the Cache on Demand with cacheTag

The cacheTag function enables you to invalidate the cache on demand. You provide a key to identify a cached value, and then later use this key to invalidate the cache when the underlying data changes. This is typically done after a database update.

Granular Caching with Components and Functions

The use cache directive can be applied at different levels – to an entire route, to individual components, or even to specific functions and server actions. This allows for highly granular control over caching behavior.

Example: Dynamic Price, Cached Description

The video demonstrates separating the price data fetching and UI into its own component and wrapping this component with the React Suspense component to achieve a 'streaming' result where the description is rendered immediately while the price loads in the background. The product description fetching function can be tagged as use cache while the price is not.

Conclusion

The new Dynamic IO API in Next.js 15 represents a significant step forward in simplifying caching. While still experimental, it offers a more intuitive and flexible approach to managing cached data. By understanding use cache and Suspense, developers can effectively optimize the performance of their Next.js applications.

It's also worth noting the mention of React 19 and the React Compiler which aims to minimize the need for hooks like useMemo and useCallback which will improve code maintainability.