Miguel Palhas
100 lines
4.4 KiB
Markdown
100 lines
4.4 KiB
Markdown
---
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description: React and Next.js performance optimization guidelines from Vercel Engineering. 45 rules across 8 categories, prioritized by impact.
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---
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# Vercel React Best Practices
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Comprehensive performance optimization guide for React and Next.js applications. 45 rules across 8 categories, prioritized by impact.
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## When to Apply
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- Writing new React components or Next.js pages
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- Implementing data fetching (client or server-side)
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- Reviewing code for performance issues
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- Refactoring existing React/Next.js code
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- Optimizing bundle size or load times
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## Rule Categories by Priority
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| Priority | Category | Impact | Prefix |
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|----------|----------|--------|--------|
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| 1 | Eliminating Waterfalls | CRITICAL | `async-` |
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| 2 | Bundle Size Optimization | CRITICAL | `bundle-` |
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| 3 | Server-Side Performance | HIGH | `server-` |
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| 4 | Client-Side Data Fetching | MEDIUM-HIGH | `client-` |
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| 5 | Re-render Optimization | MEDIUM | `rerender-` |
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| 6 | Rendering Performance | MEDIUM | `rendering-` |
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| 7 | JavaScript Performance | LOW-MEDIUM | `js-` |
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| 8 | Advanced Patterns | LOW | `advanced-` |
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## 1. Eliminating Waterfalls (CRITICAL)
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- **async-defer-await** - Move await into branches where actually used
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- **async-parallel** - Use Promise.all() for independent operations
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- **async-dependencies** - Use better-all for partial dependencies
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- **async-api-routes** - Start promises early, await late in API routes
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- **async-suspense-boundaries** - Use Suspense to stream content
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## 2. Bundle Size Optimization (CRITICAL)
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- **bundle-barrel-imports** - Import directly, avoid barrel files
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- **bundle-dynamic-imports** - Use next/dynamic for heavy components
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- **bundle-defer-third-party** - Load analytics/logging after hydration
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- **bundle-conditional** - Load modules only when feature is activated
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- **bundle-preload** - Preload on hover/focus for perceived speed
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## 3. Server-Side Performance (HIGH)
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- **server-cache-react** - Use React.cache() for per-request deduplication
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- **server-cache-lru** - Use LRU cache for cross-request caching
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- **server-serialization** - Minimize data passed to client components
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- **server-parallel-fetching** - Restructure components to parallelize fetches
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- **server-after-nonblocking** - Use after() for non-blocking operations
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## 4. Client-Side Data Fetching (MEDIUM-HIGH)
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- **client-swr-dedup** - Use SWR for automatic request deduplication
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- **client-event-listeners** - Deduplicate global event listeners
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## 5. Re-render Optimization (MEDIUM)
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- **rerender-defer-reads** - Don't subscribe to state only used in callbacks
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- **rerender-memo** - Extract expensive work into memoized components
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- **rerender-dependencies** - Use primitive dependencies in effects
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- **rerender-derived-state** - Subscribe to derived booleans, not raw values
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- **rerender-functional-setstate** - Use functional setState for stable callbacks
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- **rerender-lazy-state-init** - Pass function to useState for expensive values
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- **rerender-transitions** - Use startTransition for non-urgent updates
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## 6. Rendering Performance (MEDIUM)
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- **rendering-animate-svg-wrapper** - Animate div wrapper, not SVG element
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- **rendering-content-visibility** - Use content-visibility for long lists
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- **rendering-hoist-jsx** - Extract static JSX outside components
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- **rendering-svg-precision** - Reduce SVG coordinate precision
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- **rendering-hydration-no-flicker** - Use inline script for client-only data
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- **rendering-activity** - Use Activity component for show/hide
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- **rendering-conditional-render** - Use ternary, not && for conditionals
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## 7. JavaScript Performance (LOW-MEDIUM)
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- **js-batch-dom-css** - Group CSS changes via classes or cssText
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- **js-index-maps** - Build Map for repeated lookups
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- **js-cache-property-access** - Cache object properties in loops
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- **js-cache-function-results** - Cache function results in module-level Map
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- **js-cache-storage** - Cache localStorage/sessionStorage reads
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- **js-combine-iterations** - Combine multiple filter/map into one loop
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- **js-length-check-first** - Check array length before expensive comparison
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- **js-early-exit** - Return early from functions
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- **js-hoist-regexp** - Hoist RegExp creation outside loops
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- **js-min-max-loop** - Use loop for min/max instead of sort
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- **js-set-map-lookups** - Use Set/Map for O(1) lookups
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- **js-tosorted-immutable** - Use toSorted() for immutability
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## 8. Advanced Patterns (LOW)
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- **advanced-event-handler-refs** - Store event handlers in refs
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- **advanced-use-latest** - useLatest for stable callback refs
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$ARGUMENTS
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