React Best Practices

React Best Practices

Comprehensive performance optimization guide for React and Next.js applications from Vercel Engineering. Contains 57 rules across 8 categories, prioritized by impact.

Installation

OpenClaw / Moltbot / Clawbot

npx clawhub@latest install react-best-practices

WHAT This Skill Does

Provides actionable rules for:

• Eliminating request waterfalls
• Optimizing bundle size
• Improving server-side performance
• Efficient client-side data fetching
• Minimizing re-renders
• Rendering performance optimizations
• JavaScript micro-optimizations
• Advanced patterns for edge cases

WHEN To Use

• Writing new React components or Next.js pages
• Implementing data fetching (client or server-side)
• Reviewing code for performance issues
• Refactoring React/Next.js applications
• Optimizing bundle size or load times
• Debugging slow renders or waterfalls

KEYWORDS

react performance, nextjs optimization, bundle size, waterfalls, suspense, server components, rsc, rerender, usememo, dynamic import, parallel fetching, cache, swr

Rule Categories by Priority

Quick Reference

1. Eliminating Waterfalls (CRITICAL)

2. Bundle Size Optimization (CRITICAL)

3. Server-Side Performance (HIGH)

4. Client-Side Data Fetching (MEDIUM-HIGH)

5. Re-render Optimization (MEDIUM)

6. Rendering Performance (MEDIUM)

7. JavaScript Performance (LOW-MEDIUM)

8. Advanced Patterns (LOW)

How to Use

Reading Individual Rules

Each rule file in rules/ contains:

• Brief explanation of why it matters
• Incorrect code example with explanation
• Correct code example with explanation
• Additional context and references

rules/async-parallel.md
rules/bundle-barrel-imports.md
rules/rerender-memo.md

Full Compiled Document

For the complete guide with all rules expanded: AGENTS.md

This 2900+ line document contains every rule with full code examples and detailed explanations, suitable for comprehensive reference.

Key Patterns

Parallel Data Fetching

// Bad: sequential
const user = await fetchUser()
const posts = await fetchPosts()

// Good: parallel
const [user, posts] = await Promise.all([
  fetchUser(),
  fetchPosts()
])

Dynamic Imports

// Bad: bundles Monaco with main chunk
import { MonacoEditor } from './monaco-editor'

// Good: loads on demand
const MonacoEditor = dynamic(
  () => import('./monaco-editor').then(m => m.MonacoEditor),
  { ssr: false }
)

Functional setState

// Bad: stale closure risk
const addItem = useCallback((item) => {
  setItems([...items, item])
}, [items]) // recreates on every items change

// Good: always uses latest state
const addItem = useCallback((item) => {
  setItems(curr => [...curr, item])
}, []) // stable reference

NEVER Do

1. NEVER await operations sequentially when they can run in parallel
2. NEVER import from barrel files (import { X } from 'lib') — import directly
3. NEVER skip authentication in Server Actions — treat them like API routes
4. NEVER pass entire objects to client components when only one field is needed
5. NEVER use && for conditional rendering with numbers — use ternary
6. NEVER subscribe to state only used in event handlers — read on demand
7. NEVER mutate arrays with .sort() — use .toSorted()
8. NEVER put initialization in useEffect([]) — use module-level guard