react-best-practices

# React Best Practices Performance optimization guide for client-side React applications. Contains 47 rules across 8 categories, prioritized by impact. Adapted from Vercel Engineering's guidelines, filtered for client-only React + Vite (no Next.js / SSR). ## When to Apply Reference these guidelines when: - Writing new React components or hooks - Reviewing code for performance issues - Refactoring existing React code - Optimizing bundle size or render performance - Writing or reviewing `useEffect` usage ## Rule Categories by Priority | Priority | Category | Impact | Prefix | |----------|----------|--------|--------| | 1 | Eliminating Waterfalls | CRITICAL | `async-` | | 2 | Bundle Size Optimization | CRITICAL | `bundle-` | | 3 | Client-Side Data Fetching | MEDIUM-HIGH | `client-` | | 4 | Re-render Optimization | MEDIUM | `rerender-` | | 5 | useEffect Patterns | MEDIUM | `useeffect-` | | 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 promise chaining for partial dependencies - `async-api-routes` — Start promises early, await late ### 2. Bundle Size Optimization (CRITICAL) - `bundle-barrel-imports` — Import directly, avoid barrel files - `bundle-conditional` — Load modules only when feature is activated - `bundle-defer-third-party` — Load analytics/logging after mount - `bundle-preload` — Preload on hover/focus for perceived speed ### 3. Client-Side Data Fetching (MEDIUM-HIGH) - `client-event-listeners` — Deduplicate global event listeners - `client-passive-event-listeners` — Use passive listeners for scroll/touch - `client-swr-dedup` — Use SWR for automatic request deduplication - `client-localstorage-schema` — Version and minimize localStorage data ### 4. Re-render Optimization (MEDIUM) - `rerender-derived-state-no-effect` — Derive state during render, not effects - `rerender-defer-reads` — Don't subscribe to state only used in callbacks - `rerender-simple-expression-in-memo` — Avoid memo for simple primitives - `rerender-memo-with-default-value` — Hoist default non-primitive props - `rerender-memo` — Extract expensive work into memoized components - `rerender-dependencies` — Use primitive dependencies in effects - `rerender-move-effect-to-event` — Put interaction logic in event handlers - `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 - `rerender-use-ref-transient-values` — Use refs for transient frequent values ### 5. useEffect Patterns (MEDIUM) - `useeffect-anti-patterns` — Common mistakes: derived state in effects, effect chains, notifying parents - `useeffect-alternatives` — Decision tree and alternatives: derived state, key prop, event handlers, useSyncExternalStore ### 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-conditional-render` — Use ternary, not && for conditionals - `rendering-usetransition-loading` — Prefer useTransition for loading state ### 7. JavaScript Performance (LOW-MEDIUM) - `js-batch-dom-css` — Batch DOM reads/writes to avoid layout thrashing - `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-init-once` — Initialize app once per app load - `advanced-event-handler-refs` — Store event handlers in refs - `advanced-use-latest` — useEffectEvent for stable callback refs ## How to Use Read individual reference files for detailed explanations and code examples: ``` references/async-parallel.md references/rerender-derived-state-no-effect.md references/useeffect-anti-patterns.md ``` Each reference file contains: - Brief explanation of why it matters - Incorrect code example with explanation - Correct code example with explanation - Additional context and references