nextjs-server-navigation（Next.js server navigation 安全）

Next.js: Server Component Navigation Pattern

⚠️ CRITICAL RULE

Server Components use DIFFERENT navigation methods than Client Components!

When requirements call for server-rendered navigation—for example, linking to other pages, redirecting after a check, or demonstrating routing patterns—prefer <Link> and redirect() within Server Components. You still avoid 'use client' unless a client-only API is involved.

The Pattern

Scenario: build a server component that demonstrates proper navigation patterns

✅ CORRECT Solution:

// app/page.tsx (Server Component - NO 'use client'!)
import Link from 'next/link';

export default async function Page() {
  return (
    <div>
      <h1>Home</h1>
      <Link href="/dashboard">Go to Dashboard</Link>
      <Link href="/profile">View Profile</Link>
    </div>
  );
}

❌ WRONG Solution:

// app/page.tsx
'use client';  // ❌ NO! Server components don't need this for navigation!

import { useRouter } from 'next/navigation';  // ❌ Wrong for server components

export default function Page() {
  const router = useRouter();  // ❌ This is client-side navigation
  // ...
}

Server Navigation Methods

Method 1: Link Component (Recommended for Links)

// app/page.tsx
import Link from 'next/link';

export default async function Page() {
  // Can still fetch data - this is a server component!
  const data = await fetchData();

  return (
    <div>
      <h1>Welcome</h1>

      {/* Simple navigation link */}
      <Link href="/about">About Us</Link>

      {/* Dynamic link */}
      <Link href={`/products/${data.productId}`}>View Product</Link>

      {/* Link with styling */}
      <Link href="/dashboard" className="btn-primary">
        Dashboard
      </Link>
    </div>
  );
}

Key Points:

• ✅ Works in Server Components (no 'use client' needed)
• ✅ Can be async function
• ✅ Can fetch data
• ✅ No hooks required

Method 2: redirect() Function (For Conditional Redirects)

// app/profile/page.tsx
import { redirect } from 'next/navigation';
import { cookies } from 'next/headers';

export default async function ProfilePage() {
  // Check authentication
  const cookieStore = await cookies();
  const session = cookieStore.get('session');

  // Redirect if not authenticated
  if (!session) {
    redirect('/login');
  }

  // Fetch user data
  const user = await fetchUser(session.value);

  return <div>Welcome, {user.name}!</div>;
}

When to use redirect():

• Conditional redirects based on server-side data
• Authentication checks
• Permission validation
• Data-based routing

Method 3: Button with Server Action

// app/page.tsx
import { logout } from './actions';

export default async function Page() {
  return (
    <div>
      <h1>Dashboard</h1>

      <form action={logout}>
        <button type="submit">Logout</button>
      </form>
    </div>
  );
}

// app/actions.ts
'use server';

import { redirect } from 'next/navigation';

export async function logout() {
  // Clear session
  await clearSession();

  // Redirect to login page
  redirect('/login');
}

Complete Example: Navigation Patterns

// app/page.tsx - Demonstrates multiple navigation patterns

import Link from 'next/link';
import { redirect } from 'next/navigation';
import { headers } from 'next/headers';

export default async function HomePage() {
  // Server-side logic
  const headersList = await headers();
  const userAgent = headersList.get('user-agent');

  // Conditional redirect example
  if (userAgent?.includes('bot')) {
    redirect('/bot-page');
  }

  return (
    <div>
      <h1>Welcome to Our App</h1>

      {/* Navigation Links */}
      <nav>
        <Link href="/about">About</Link>
        <Link href="/products">Products</Link>
        <Link href="/contact">Contact</Link>
      </nav>

      {/* Button-style link */}
      <Link href="/get-started" className="button">
        Get Started
      </Link>

      {/* Dynamic link */}
      <Link href={`/user/${123}`}>View Profile</Link>
    </div>
  );
}

TypeScript: NEVER Use any Type

// ❌ WRONG
function handleClick(e: any) { ... }

// ✅ CORRECT - Not needed in server components!
// Server components don't have onClick handlers

// For client components with handlers:
'use client';
function handleClick(e: React.MouseEvent<HTMLButtonElement>) { ... }

Server vs Client Navigation Comparison

Common Mistakes to Avoid

❌ Mistake 1: Adding 'use client' for Navigation

// ❌ WRONG
'use client';  // Don't add this just for navigation!

import Link from 'next/link';

export default function Page() {
  return <Link href="/about">About</Link>;
}

// ✅ CORRECT
import Link from 'next/link';

// No 'use client' needed!
export default async function Page() {
  return <Link href="/about">About</Link>;
}

❌ Mistake 2: Using useRouter() in Server Component

// ❌ WRONG
import { useRouter } from 'next/navigation';  // This is for CLIENT components!

export default async function Page() {
  const router = useRouter();  // ERROR! Can't use hooks in server components
  // ...
}

// ✅ CORRECT - Use Link or redirect()
import Link from 'next/link';
import { redirect } from 'next/navigation';

export default async function Page() {
  // Conditional redirect
  const shouldRedirect = await checkSomething();
  if (shouldRedirect) {
    redirect('/other-page');
  }

  // Or navigation links
  return <Link href="/other-page">Go</Link>;
}

❌ Mistake 3: Making Component Client-Side for Simple Navigation

// ❌ WRONG - Loses server component benefits!
'use client';

export default function Page() {
  return (
    <div>
      <Link href="/dashboard">Dashboard</Link>
    </div>
  );
}

// ✅ CORRECT - Keep it as a server component!
export default async function Page() {
  // Can now fetch data server-side
  const data = await fetchData();

  return (
    <div>
      <Link href="/dashboard">Dashboard</Link>
      <p>{data.message}</p>
    </div>
  );
}

Advanced Patterns

Programmatic Navigation in Server Actions

// app/page.tsx
import { createPost } from './actions';

export default async function Page() {
  return (
    <form action={createPost}>
      <input name="title" required />
      <button type="submit">Create Post</button>
    </form>
  );
}

// app/actions.ts
'use server';

import { redirect } from 'next/navigation';

export async function createPost(formData: FormData) {
  const title = formData.get('title') as string;

  // Save to database
  const post = await db.posts.create({ title });

  // Redirect to the new post
  redirect(`/posts/${post.id}`);
}

Multiple Links in Server Component

// app/page.tsx
import Link from 'next/link';

export default async function NavigationPage() {
  const pages = await fetchPages();

  return (
    <nav>
      <h2>Site Navigation</h2>
      <ul>
        {pages.map((page) => (
          <li key={page.id}>
            <Link href={`/pages/${page.slug}`}>
              {page.title}
            </Link>
          </li>
        ))}
      </ul>
    </nav>
  );
}

Quick Decision Tree

Need navigation in a component?
│
├─ Is it a Server Component (no 'use client')?
│  ├─ Static link → Use <Link>
│  ├─ Conditional redirect → Use redirect()
│  └─ Form submission → Server Action with redirect()
│
└─ Is it a Client Component ('use client')?
   ├─ Link → Use <Link> (works in both!)
   └─ Programmatic → Use useRouter()

When to Use Client-Side Navigation Instead

Use Client Components ('use client' + useRouter()) ONLY when you need:

• Programmatic navigation based on client state
• Navigation after client-side animations
• Browser-only APIs (window, localStorage)
• React hooks (useState, useEffect)

For everything else, use Server Component navigation!

Quick Checklist

When you see "demonstrates navigation patterns":

• Create a server component (no 'use client')
• Import Link from 'next/link'
• Add <Link> components with href prop
• Keep component as async if fetching data
• Do NOT import useRouter from next/navigation
• Do NOT add 'use client' directive
• Use proper TypeScript types (no any)

Summary

Server Component Navigation:

• ✅ Use <Link> for navigation links
• ✅ Use redirect() for conditional redirects
• ✅ Keep component async if needed
• ✅ No 'use client' required
• ✅ No hooks needed

This pattern is simpler and more performant than client-side navigation for static links!