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React Best Practices

supercent-io/skills-template
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This skill provides comprehensive best practices for optimizing React and Next.js applications, focusing on performance enhancements such as reducing bundle size, improving server-side and client-side rendering, and minimizing re-renders. It offers 45 prioritized rules across categories like eliminating waterfalls, bundle size, and re-render optimization, designed to guide automated code refactoring and review processes. Ideal for developers writing, reviewing, or refactoring React and Next.js code to enhance application speed and efficiency.

npx skills add https://github.com/supercent-io/skills-template --skill react-best-practices

Vercel React Best Practices

Comprehensive performance optimization guide for React and Next.js applications, maintained by Vercel. Contains 45 rules across 8 categories, prioritized by impact to guide automated refactoring and code generation.

When to Apply

Reference these guidelines when:

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

Rule Categories by Priority

Priority Category Impact 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)

  • 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)

  • 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)

  • server-cache-react - Use React.cache() for per-request deduplication
  • server-cache-lru - Use LRU cache for cross-request caching
  • 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)

  • client-swr-dedup - Use SWR for automatic request deduplication
  • client-event-listeners - Deduplicate global event listeners

5. Re-render Optimization (MEDIUM)

  • rerender-defer-reads - Don't subscribe to state only used in callbacks
  • rerender-memo - Extract expensive work into memoized components
  • rerender-dependencies - Use primitive dependencies in effects
  • rerender-derived-state - Subscribe to derived booleans, not raw values
  • rerender-functional-setstate - Use functional setState for stable callbacks
  • rerender-lazy-state-init - Pass function to useState for expensive values
  • rerender-transitions - Use startTransition for non-urgent updates

6. Rendering Performance (MEDIUM)

  • 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-activity - Use Activity component for show/hide
  • rendering-conditional-render - Use ternary, not && for conditionals

7. JavaScript Performance (LOW-MEDIUM)

  • 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 comparison
  • 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)

  • advanced-event-handler-refs - Store event handlers in refs
  • advanced-use-latest - useLatest for stable callback refs

How to Use

For detailed explanations and code examples, read the full compiled document: AGENTS.md Each rule contains:

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

Key Examples

Promise.all for Independent Operations (CRITICAL)

// ❌ Sequential: 3 round trips
const user = await fetchUser()
const posts = await fetchPosts()
const comments = await fetchComments()
// ✅ Parallel: 1 round trip
const [user, posts, comments] = await Promise.all([
  fetchUser(),
  fetchPosts(),
  fetchComments()
])

Avoid Barrel File Imports (CRITICAL)

// ❌ Imports entire library (200-800ms import cost)
import { Check, X, Menu } from 'lucide-react'
// ✅ Imports only what you need
import Check from 'lucide-react/dist/esm/icons/check'
import X from 'lucide-react/dist/esm/icons/x'

Dynamic Imports for Heavy Components (CRITICAL)

// ❌ Monaco bundles with main chunk ~300KB
import { MonacoEditor } from './monaco-editor'
// ✅ Monaco loads on demand
import dynamic from 'next/dynamic'
const MonacoEditor = dynamic(
  () => import('./monaco-editor').then(m => m.MonacoEditor),
  { ssr: false }
)

Use Functional setState (MEDIUM)

// ❌ Requires state as dependency, stale closure risk
const addItems = useCallback((newItems) => {
  setItems([...items, ...newItems])
}, [items])
// ✅ Stable callback, no stale closures
const addItems = useCallback((newItems) => {
  setItems(curr => [...curr, ...newItems])
}, [])

Constraints

Required Rules (MUST)

  1. Eliminate waterfalls: Use Promise.all, Suspense
  2. Bundle optimization: Prohibit barrel imports, use dynamic imports
  3. RSC boundaries: Serialize only the data you need

Prohibited (MUST NOT)

  1. Sequential await: Do not run independent fetches sequentially
  2. Array mutations: Use toSorted() instead of sort()
  3. Inline objects in React.cache: Causes cache misses

References

Metadata

Version

  • Current version: 1.0.0
  • Last updated: 2026-01-22
  • Supported platforms: Claude, ChatGPT, Gemini
  • Source: vercel/agent-skills

Related Skills

Tags

#React #Next.js #performance #optimization #vercel #waterfalls #bundle-size #RSC #frontend

GitHub Owner

Owner: shuding

GitHub Links

Files

performance-optimization

state-management

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