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Next.js 15 Performance Improvements: What's New and How to Use Them

Next.js 15 brings significant performance improvements and new features that make building fast web applications easier than ever. In this post, I'll explore the key improvements and how to leverage them in your projects.

The New Compiler

One of the most exciting features in Next.js 15 is the new Rust-based compiler. This compiler provides:

  • Faster builds: Up to 5x faster than the previous JavaScript-based compiler
  • Better tree shaking: More efficient code elimination
  • Improved error messages: Clearer debugging experience

Enabling the New Compiler

To use the new compiler, update your next.config.js:

/** @type {import('next').NextConfig} */
const nextConfig = {
  experimental: {
    turbo: {
      rules: {
        '*.svg': {
          loaders: ['@svgr/webpack'],
          as: '*.js',
        },
      },
    },
  },
};

module.exports = nextConfig;

Enhanced Caching Strategy

Next.js 15 introduces improved caching mechanisms that significantly boost performance:

Partial Prerendering

Partial prerendering allows you to prerender static parts of your page while keeping dynamic content server-side rendered:

// app/page.tsx
import { Suspense } from 'react'
import { DynamicContent } from './components/DynamicContent'

export default function Page() {
  return (
    <div>
      {/* This content is prerendered */}
      <h1>Welcome to our site</h1>
      <p>This content is static and fast</p>

      {/* This content is server-side rendered */}
      <Suspense fallback={<div>Loading...</div>}>
        <DynamicContent />
      </Suspense>
    </div>
  )
}

Improved Image Optimization

The new next/image component includes better optimization:

import Image from 'next/image'

export default function OptimizedImage() {
  return (
    <Image
      src="/hero-image.jpg"
      alt="Hero image"
      width={1200}
      height={600}
      priority
      placeholder="blur"
      blurDataURL="data:image/jpeg;base64,..."
    />
  )
}

Server Actions Improvements

Server Actions in Next.js 15 are now more performant and easier to use:

// app/actions.ts
'use server';

import { revalidatePath } from 'next/cache';

export async function createPost(formData: FormData) {
  const title = formData.get('title') as string;
  const content = formData.get('content') as string;

  // Validate input
  if (!title || !content) {
    throw new Error('Title and content are required');
  }

  // Save to database
  await db.post.create({
    data: { title, content },
  });

  // Revalidate the posts page
  revalidatePath('/posts');
}

Bundle Analysis and Optimization

Next.js 15 includes better bundle analysis tools:

# Generate bundle analysis
pnpm build --analyze

This generates a detailed report showing:

  • Bundle sizes
  • Duplicate dependencies
  • Unused code
  • Import optimization opportunities

Performance Monitoring

The new performance monitoring features help you track real-world performance:

// app/layout.tsx
import { Analytics } from '@vercel/analytics/react'

export default function RootLayout({
  children,
}: {
  children: React.ReactNode
}) {
  return (
    <html lang="en">
      <body>
        {children}
        <Analytics />
      </body>
    </html>
  )
}

Best Practices for Next.js 15

1. Use the App Router

The App Router provides better performance and features:

// app/blog/[slug]/page.tsx
export async function generateStaticParams() {
  const posts = await getPosts()
  return posts.map((post) => ({
    slug: post.slug,
  }))
}

export default async function BlogPost({ params }: { params: { slug: string } }) {
  const post = await getPost(params.slug)
  return <article>{post.content}</article>
}

2. Implement Proper Caching

// app/api/posts/route.ts
import { NextResponse } from 'next/server';

export async function GET() {
  const posts = await db.post.findMany({
    orderBy: { createdAt: 'desc' },
  });

  return NextResponse.json(posts, {
    headers: {
      'Cache-Control': 'public, s-maxage=3600, stale-while-revalidate=86400',
    },
  });
}

3. Optimize Fonts

// app/layout.tsx
import { Inter } from 'next/font/google'

const inter = Inter({
  subsets: ['latin'],
  display: 'swap',
  variable: '--font-inter',
})

export default function RootLayout({
  children,
}: {
  children: React.ReactNode
}) {
  return (
    <html lang="en" className={inter.variable}>
      <body className={inter.className}>{children}</body>
    </html>
  )
}

Migration Guide

If you're upgrading from Next.js 14, here are the key steps:

  1. Update dependencies:

    pnpm update next@latest react@latest react-dom@latest

  2. Enable the new compiler in your config

  3. Update image components to use new optimization features

  4. Review server actions for new patterns

  5. Test performance with the new monitoring tools

Conclusion

Next.js 15 represents a significant step forward in web application performance. The new compiler, enhanced caching, and improved developer experience make it easier than ever to build fast, scalable applications.

The key is to leverage these new features appropriately for your use case. Start with the new compiler and partial prerendering, then gradually adopt other features as needed.

Remember to measure performance improvements in your specific application, as the benefits will vary depending on your codebase and requirements.

What performance improvements are you most excited about in Next.js 15? Let me know in the comments below!

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