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


async-
bundle-
server-
client-
rerender-
rendering-
js-
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

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

React Best Practices

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