Next.js 15: New Features and Performance Improvements

Next.js 15 represents a significant milestone in the React ecosystem. The features and performance improvements coming with this new version will greatly enhance our web development experience.

Turbopack Integration

One of the most important innovations of Next.js 15 is Turbopack becoming stable. This new bundler offers much faster build times compared to Webpack.

Performance Comparison:

React 19 Support

Next.js 15 supports all the new features of React 19:

• React Server Components: First-class support for RSC
• React Compiler: Automatic optimizations
• Suspense Improvements: Better streaming capabilities

Enhanced Image Component

The Image component has been significantly improved:

import { Image } from 'next/image'

// New responsive features
function HeroImage() {
  return (
    <Image
      src="/hero.jpg"
      alt="Hero image"
      quality={90}
      priority
      fill
      sizes="(max-width: 768px) 100vw, 50vw"
      style={{ objectFit: "cover" }}
    />
  )
}

The new features include:

• Better lazy loading algorithms
• Improved image formats (AVIF support)
• Enhanced responsive design options

Middleware Enhancements

Middleware has been greatly improved in Next.js 15:

// middleware.ts
import { NextResponse } from 'next/server'
import type { NextRequest } from 'next/server'

export function middleware(request: NextRequest) {
  const country = request.geo?.country || 'US'
  const language = request.headers.get('accept-language')?.split(',')[0] || 'en-US'
  
  // Advanced routing based on user data
  if (country === 'DE') {
    return NextResponse.redirect(new URL('/de', request.url))
  }
  
  // Enhanced response capabilities
  const response = NextResponse.next()
  response.headers.set('x-custom-header', 'value')
  
  return response
}

export const config = {
  matcher: ['/((?!api|_next/static|favicon.ico).*)'],
}

New capabilities include:

• Better authentication integration
• Enhanced geographical targeting
• Improved caching controls

Server Actions

Server Actions are now a stable feature in Next.js 15:

// app/actions.ts
'use server'

export async function submitForm(formData: FormData) {
  const name = formData.get('name')
  const email = formData.get('email')
  
  // Process form submission on the server
  await saveToDatabase({ name, email })
  
  // Return data to the client
  return { success: true }
}

// app/form.tsx
'use client'

import { submitForm } from './actions'

export default function Form() {
  return (
    <form action={submitForm}>
      <input name="name" type="text" />
      <input name="email" type="email" />
      <button type="submit">Submit</button>
    </form>
  )
}

Improved Routing System

Next.js 15 builds on the App Router with several improvements:

• Parallel Routes: Better composition of UI elements
• Intercepting Routes: Enhanced modal and overlay experiences
• Route Handlers: More powerful API endpoints

Performance Metrics

Next.js 15 shows significant performance improvements:

• 40% faster page loads (Core Web Vitals)
• 30% reduction in JavaScript bundle size
• 50% improvement in build times with Turbopack

Conclusion

Next.js 15 brings many significant improvements that enhance both developer experience and end-user performance. With stable Turbopack integration, React 19 support, and enhanced server components, it's a compelling upgrade for any project.

The new features make it easier to build complex, high-performing web applications while maintaining excellent user experiences. If you haven't upgraded yet, now is the perfect time to do so.