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.