React Server Components in Next.js Overview

React Server Components (RSC) allow components to render on the server, reducing client-side JavaScript and enabling direct data access. In Next.js App Router, all components are Server Components by default.

Server vs Client Components Server Components (Default)

Server Components run only on the server:

// app/users/page.tsx (Server Component - default) async function UsersPage() { const users = await db.user.findMany() // Direct DB access

return (

{user.name}

) }

Benefits:

Direct database/filesystem access Keep sensitive data on server (API keys, tokens) Reduce client bundle size Automatic code splitting Client Components

Add 'use client' directive for interactivity:

// components/counter.tsx 'use client'

import { useState } from 'react'

export function Counter() { const [count, setCount] = useState(0)

return ( ) }

Use Client Components for:

useState, useEffect, useReducer Event handlers (onClick, onChange) Browser APIs (window, document) Custom hooks with state The Mental Model

Think of the component tree as having a "client boundary":

Server Component (page.tsx) ├── Server Component (header.tsx) ├── Client Component ('use client') ← boundary │ ├── Client Component (child) │ └── Client Component (child) └── Server Component (footer.tsx)

Key rules:

Server Components can import Client Components Client Components cannot import Server Components You can pass Server Components as children to Client Components Composition Patterns Pattern 1: Server Data → Client Interactivity

Fetch data in Server Component, pass to Client:

// app/products/page.tsx (Server) import { ProductList } from './product-list'

export default async function ProductsPage() { const products = await getProducts() return }

// app/products/product-list.tsx (Client) 'use client'

export function ProductList({ products }: { products: Product[] }) { const [filter, setFilter] = useState('')

const filtered = products.filter(p => p.name.includes(filter) )

return ( <> setFilter(e.target.value)} /> {filtered.map(p => )} </> ) }

Pattern 2: Children as Server Components

Pass Server Components through children prop:

// components/client-wrapper.tsx 'use client'

export function ClientWrapper({ children }: { children: React.ReactNode }) { const [isOpen, setIsOpen] = useState(false)

return (

{isOpen && children} {/ Server Component content /}

) }

// app/page.tsx (Server) import { ClientWrapper } from '@/components/client-wrapper' import { ServerContent } from '@/components/server-content'

export default function Page() { return ( {/ Renders on server! /} ) }

Pattern 3: Slots for Complex Layouts

Use multiple children slots:

// components/dashboard-shell.tsx 'use client'

interface Props { sidebar: React.ReactNode main: React.ReactNode }

export function DashboardShell({ sidebar, main }: Props) { const [collapsed, setCollapsed] = useState(false)

return (

{!collapsed && }

{main}

) }

Data Fetching Async Server Components

Server Components can be async:

// app/posts/page.tsx export default async function PostsPage() { const posts = await fetch('https://api.example.com/posts') .then(res => res.json())

return (

{post.title}

) }

Parallel Data Fetching

Fetch multiple resources in parallel:

export default async function DashboardPage() { const [user, posts, analytics] = await Promise.all([ getUser(), getPosts(), getAnalytics(), ])

return ( ) }

Streaming with Suspense

Stream slow components:

import { Suspense } from 'react'

export default function Page() { return (

{/ Renders immediately /} }> {/ Streams when ready /}

) }

Decision Guide

Use Server Component when:

Fetching data Accessing backend resources Keeping sensitive info on server Reducing client JavaScript Component has no interactivity

Use Client Component when:

Using state (useState, useReducer) Using effects (useEffect) Using event listeners Using browser APIs Using custom hooks with state Common Mistakes Don't add 'use client' unnecessarily - it increases bundle size Don't try to import Server Components into Client Components Do serialize data at boundaries (no functions, classes, or dates) Do use the children pattern for composition Resources

For detailed patterns, see:

references/server-vs-client.md - Complete comparison guide references/composition-patterns.md - Advanced composition examples/data-fetching-patterns.md - Data fetching examples

server-components

安装