Nextjs Server Components

When to Use

When building Next.js App Router pages and deciding between Server and Client Components.

Patterns

Default: Server Components

// app/page.tsx - Server Component by default
async function Page() {
  const data = await db.query('SELECT * FROM posts');
  return <PostList posts={data} />;
}

// ✅ Direct DB/API access
// ✅ Secrets safe (never sent to client)
// ✅ Zero client JS for this component

Client Component ("use client")

'use client'
// Only add when you NEED:
// - useState, useEffect, useContext
// - Event handlers (onClick, onChange)
// - Browser APIs (localStorage, window)

import { useState } from 'react';

export function Counter() {
  const [count, setCount] = useState(0);
  return <button => setCount(c => c + 1)}>{count}</button>;
}

Composition Pattern

// Server Component (parent)
async function Dashboard() {
  const user = await getUser();
  return (
    <div>
      <UserInfo user={user} />       {/* Server */}
      <InteractiveChart />           {/* Client */}
    </div>
  );
}

// Pass server data to client as props
<ClientComponent initialData={serverData} />

Data Fetching in Server Components

// ✅ Parallel fetching
async function Page() {
  const [posts, user] = await Promise.all([
    getPosts(),
    getUser()
  ]);
  return <Feed posts={posts} user={user} />;
}

Anti-Patterns

• Adding "use client" to every component (defeats RSC benefits)
• Importing server-only code in client components
• Passing functions as props from Server to Client
• Using useEffect for data that could be fetched on server

Verification Checklist

• "use client" only where actually needed
• No secrets in client components
• Server data passed as serializable props
• Parallel data fetching where possible