Next.js: When to Use Server Components vs Client Components

Introduction

Next.js 14’s App Router introduced Server Components (RSCs), but when should you use them vs Client Components? Let’s break it down.

What Are Server Components?

• Rendered on the server (zero client-side JS).

• No React hooks (useState, useEffect).

• Direct database/API access (secure).

When to Use Server Components

1. Static Content (Blog posts, product pages).

2. Data Fetching (No need for getServerSideProps).

3. Sensitive Logic (API keys, auth checks).

When to Use Client Components

1. Interactivity (Forms, animations).

2. Browser APIs (localStorage, window).

3. State Management (Redux, Zustand).

Example: Hybrid Blog Page

// app/blog/[slug]/page.js (Server Component)
async function BlogPost({ params }) {
  const post = await fetchPost(params.slug); // DB call
  
  return (
    <article>
      <h1>{post.title}</h1>
      <p>{post.content}</p>
      <CommentsSection postId={post.id} /> 
    </article>
  );
}

// app/components/CommentsSection.js (Client Component)
'use client';
function CommentsSection({ postId }) {
  const [comments, setComments] = useState([]);
  // Fetch on client
  useEffect(() => fetchComments(postId), [postId]);
  return <div>{comments.map(...)}</div>;
}

Common Mistakes

• Overusing Client Components → Larger JS bundles.

• Fetching in Client Components → Slower than RSCs.

Conclusion

Server Components = faster, secure, SEO-friendly.
Client Components = interactivity, state.
Mix both wisely!