In the fast-paced world of web development, performance is king. Next.js 15 introduces powerful Edge Functions that allow you to execute server-side logic closer to your users than ever before. Whether you’re delivering personalized content, handling API requests, or processing server logic, Edge Functions provide unparalleled speed and scalability.

In this post, we’ll explore how Edge Functions work and demonstrate their use cases in modern web applications.

What Are Edge Functions?

Edge Functions are lightweight server-side functions executed at the edge of a Content Delivery Network (CDN). Unlike traditional server-side functions that run in centralized servers, Edge Functions run in globally distributed locations, reducing latency for users worldwide.

Key Features:

• Near-instant response times.
• Low cold start latency.
• Seamless integration with Next.js middleware.

Setting Up an Edge Function

Next.js makes it easy to configure and deploy Edge Functions. Let’s set one up step-by-step.

Step 1: Create an API Route

In your pages/api directory, create a file, e.g., pages/api/hello.ts:

export const config = {
  runtime: 'edge', // Specify the runtime as "edge"
};

export default async function handler(req: Request) {
  return new Response(JSON.stringify({ message: 'Hello from the edge!' }), {
    headers: { 'Content-Type': 'application/json' },
  });
}

Step 2: Deploy Your Edge Function

Once your API route is configured, deploy your Next.js application to Vercel. The Edge Function will automatically execute from the nearest location to the user.

Practical Use Cases

1. Personalized Content Delivery

Edge Functions can serve personalized recommendations or localized content based on user geolocation or cookies.

export default function handler(req: Request) {
  const { geo } = req.headers;
  const content =    geo?.country === 'US'
      ? 'Welcome, American visitor!'
      : 'Hello, visitor from around the world!';

  return new Response(content, {
    headers: { 'Content-Type': 'text/plain' },
  });
}

2. Authentication

Perform authentication and token validation at the edge to enhance security and reduce server load.

export default async function handler(req: Request) {
  const authToken = req.headers.get('Authorization');

  if (!authToken || !isValidToken(authToken)) {
    return new Response('Unauthorized', { status: 401 });
  }

  return new Response('Authenticated!', { status: 200 });}

3. A/B Testing

Run experiments by splitting traffic between different variations of your website.

export default function handler(req: Request) {
  const variant = Math.random() > 0.5 ? 'A' : 'B';

  return new Response(`You're seeing variant ${variant}`, {
    headers: { 'Content-Type': 'text/plain' },
  });
}

Debugging Edge Functions

Debugging Edge Functions requires logging since they don’t run in a traditional Node.js environment. Use console.log in your functions to capture runtime data.

Limitations of Edge Functions

While powerful, Edge Functions come with some limitations:

• Limited execution time.
• No access to native Node.js modules.
• Data fetching may require async solutions optimized for edge runtimes.

Conclusion

Edge Functions in Next.js 15 open up new possibilities for building high-performance web applications. By leveraging these globally distributed functions, you can enhance user experiences, reduce latency, and build scalable features tailored to your audience.

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