React Best Practices

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name: react-best-practices model: standard version: 1.0.0 description: > React and Next.js performance optimization guidelines from Vercel Engineering. 57 rules across 8 categories for writing, reviewing, and refactoring React code. tags: [react, nextjs, performance, optimization, ssr, bundle, rendering] license: MIT author: vercel

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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

| Priority | Category | Impact | Rule Prefix | |----------|----------|--------|-------------| | 1 | Eliminating Waterfalls | CRITICAL | async- | | 2 | Bundle Size Optimization | CRITICAL | bundle- | | 3 | Server-Side Performance | HIGH | server- | | 4 | Client-Side Data Fetching | MEDIUM-HIGH | client- | | 5 | Re-render Optimization | MEDIUM | rerender- | | 6 | Rendering Performance | MEDIUM | rendering- | | 7 | JavaScript Performance | LOW-MEDIUM | js- | | 8 | Advanced Patterns | LOW | advanced- |

Quick Reference

1. Eliminating Waterfalls (CRITICAL)

| Rule | Description | |------|-------------| | async-defer-await | Move await into branches where actually used | | async-parallel | Use Promise.all() for independent operations | | async-dependencies | Use better-all for partial dependencies | | async-api-routes | Start promises early, await late in API routes | | async-suspense-boundaries | Use Suspense to stream content |

2. Bundle Size Optimization (CRITICAL)

| Rule | Description | |------|-------------| | bundle-barrel-imports | Import directly, avoid barrel files | | bundle-dynamic-imports | Use next/dynamic for heavy components | | bundle-defer-third-party | Load analytics/logging after hydration | | bundle-conditional | Load modules only when feature is activated | | bundle-preload | Preload on hover/focus for perceived speed |

3. Server-Side Performance (HIGH)

| Rule | Description | |------|-------------| | server-auth-actions | Authenticate server actions like API routes | | server-cache-react | Use React.cache() for per-request dedup | | server-cache-lru | Use LRU cache for cross-request caching | | server-dedup-props | Avoid duplicate serialization in RSC props | | server-serialization | Minimize data passed to client components | | server-parallel-fetching | Restructure components to parallelize fetches | | server-after-nonblocking | Use after() for non-blocking operations |

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

| Rule | Description | |------|-------------| | client-swr-dedup | Use SWR for automatic request deduplication | | client-event-listeners | Deduplicate global event listeners | | client-passive-event-listeners | Use passive listeners for scroll | | client-localstorage-schema | Version and minimize localStorage data |

5. Re-render Optimization (MEDIUM)

| Rule | Description | |------|-------------| | rerender-defer-reads | Don't subscribe to state only used in callbacks | | rerender-memo | Extract expensive work into memoized components | | rerender-memo-with-default-value | Hoist default non-primitive props | | rerender-dependencies | Use primitive dependencies in effects | | rerender-derived-state | Subscribe to derived booleans, not raw values | | rerender-derived-state-no-effect | Derive state during render, not effects | | rerender-functional-setstate | Use functional setState for stable callbacks | | rerender-lazy-state-init | Pass function to useState for expensive values | | rerender-simple-expression-in-memo | Avoid memo for simple primitives | | rerender-move-effect-to-event | Put interaction logic in event handlers | | rerender-transitions | Use startTransition for non-urgent updates | | rerender-use-ref-transient-values | Use refs for transient frequent values |

6. Rendering Performance (MEDIUM)

| Rule | Description | |------|-------------| | rendering-animate-svg-wrapper | Animate div wrapper, not SVG element | | rendering-content-visibility | Use content-visibility for long lists | | rendering-hoist-jsx | Extract static JSX outside components | | rendering-svg-precision | Reduce SVG coordinate precision | | rendering-hydration-no-flicker | Use inline script for client-only data | | rendering-hydration-suppress-warning | Suppress expected mismatches | | rendering-activity | Use Activity component for show/hide | | rendering-conditional-render | Use ternary, not && for conditionals | | rendering-usetransition-loading | Prefer useTransition for loading state |

7. JavaScript Performance (LOW-MEDIUM)

| Rule | Description | |------|-------------| | js-batch-dom-css | Group CSS changes via classes or cssText | | js-index-maps | Build Map for repeated lookups | | js-cache-property-access | Cache object properties in loops | | js-cache-function-results | Cache function results in module-level Map | | js-cache-storage | Cache localStorage/sessionStorage reads | | js-combine-iterations | Combine multiple filter/map into one loop | | js-length-check-first | Check array length before expensive ops | | js-early-exit | Return early from functions | | js-hoist-regexp | Hoist RegExp creation outside loops | | js-min-max-loop | Use loop for min/max instead of sort | | js-set-map-lookups | Use Set/Map for O(1) lookups | | js-tosorted-immutable | Use toSorted() for immutability |

8. Advanced Patterns (LOW)

| Rule | Description | |------|-------------| | advanced-event-handler-refs | Store event handlers in refs | | advanced-init-once | Initialize app once per app load | | advanced-use-latest | useLatest for stable callback refs |

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