Exploring Next.js 15 RC: A Sneak Peek into New Features and Performance Improvements

Overview of Next.js 15 RC and React 19

With Next.js 15 Release Candidate (RC), developers get an opportunity to test significant new features before the stable release, including React 19 support, improved caching defaults, Partial Prerendering (PPR), and the experimental React Compiler. These additions are aimed at making applications faster, more efficient, and easier to manage. Let's dive into each feature and explore how they can impact modern web development.

Key Features in Next.js 15 RC

1. React 19 RC Support

The Next.js App Router is now compatible with React 19 RC, which brings exciting new APIs and features for both client and server environments. One standout feature is Actions, a new API designed to simplify client-server interactions, making it easier to handle server actions directly within components.

Note: Some third-party libraries may not yet be compatible with React 19, so check library compatibility before migrating fully.

2. Experimental React Compiler

The new React Compiler is an experimental tool that optimizes performance by minimizing the need for useMemo and useCallback, reducing the likelihood of bugs and making the code easier to maintain.

To try it out, install the babel-plugin-react-compiler and enable the experimental feature in next.config.js:

// next.config.js
const nextConfig = {
  experimental: {
    reactCompiler: true,
  },
}

module.exports = nextConfig

Or set the compiler in opt-in mode:

// next.config.js
const nextConfig = {
  experimental: {
    reactCompiler: {
      compilationMode: 'annotation',
    },
  },
}

module.exports = nextConfig

3. Caching Changes and Performance Optimizations

Caching updates in Next.js 15 RC simplify data handling by making fetch requests and GET Route Handlers uncached by default. This means data is fetched fresh with every request, enhancing dynamic behavior. However, caching can still be configured when needed:

fetch('https://api.example.com', { cache: 'force-cache' })

Client Router Cache Adjustments

In Next.js 15, Client Router Cache no longer caches Page components by default. This ensures the latest data is displayed without needing manual configuration.

4. Partial Prerendering (PPR)

Partial Prerendering (PPR) enables a mix of static and dynamic rendering within a single page. This powerful feature, now available for incremental adoption, allows developers to wrap dynamic components within Suspense, optimizing initial load time by streaming dynamic elements.

// app/page.js
import { Suspense } from 'react'
import StaticComponent from '@/app/static'
import DynamicComponent from '@/app/dynamic'

export const experimental_ppr = true

export default function Page() {
  return (
    <>
      <StaticComponent />
      <Suspense fallback={<div>Loading...</div>}>
        <DynamicComponent />
      </Suspense>
    </>
  )
}

Experimental next/after API for Post-Response Tasks

With the next/after API, you can defer tasks like logging or analytics until after a response has finished, optimizing response time. This is especially useful for background tasks that don’t need to block the user experience.

import { unstable_after as after } from 'next/server'

after(() => {
  console.log('Executing post-response task.')
})

Final Thoughts on Next.js 15 RC

The features introduced in Next.js 15 RC reflect the framework’s commitment to performance and usability. While the RC version may include breaking changes, experimenting with these features now can help teams prepare for the future and fine-tune application performance before the stable release.

Next.js continues to evolve with each update, making it an ideal choice for building high-performance, scalable web applications. Test the Next.js 15 RC today to explore its potential benefits!

References: https://nextjs.org/blog/next-15-rc