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React best practices

Skill michelve/hugin-cowork/skills/react-best-practices

A Cowork plugin that helps **product designers and engineers ship design-to-production React apps** — translating Figma mockups into accessible, production-ready components with best-practice enforcement for React 19, TypeScript, Tailwind CSS v4, and shadcn/ui.

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npx -y skills add michelve/hugin-cowork --skill react-best-practices

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This skill should be used when the user is writing, reviewing, or refactoring React code to ensure optimal performance patterns. It provides React performance optimization guidelines from Vercel Engineering, covering tasks involving React components, data fetching, bundle optimization, or performance improvements.

SKILL.md

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React Best Practices

Comprehensive performance optimization guide for React applications (Vite SPA), adapted from Vercel Engineering. Contains rules across 7 categories, prioritized by impact to guide automated refactoring and code generation.

Note: Server-side (RSC/Next.js) rules have been removed - this project uses Vite + Express, not Next.js.

When to Apply

Reference these guidelines when:

  • Writing new React components
  • Implementing data fetching (client-side with TanStack Query)
  • Reviewing code for performance issues
  • Refactoring existing React code
  • Optimizing bundle size or load times

Rule Categories by Priority

PriorityCategoryImpactPrefix
1Eliminating WaterfallsCRITICALasync-
2Bundle Size OptimizationCRITICALbundle-
3Client-Side Data FetchingMEDIUM-HIGHclient-
4Re-render OptimizationMEDIUMrerender-
5Rendering PerformanceMEDIUMrendering-
6JavaScript PerformanceLOW-MEDIUMjs-
7Advanced PatternsLOWadvanced-

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 React.lazy() 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. Client-Side Data Fetching (MEDIUM-HIGH)

  • client-tanstack-query - Use TanStack Query for automatic deduplication and caching
  • client-event-listeners - Deduplicate global event listeners
  • client-passive-event-listeners - Use passive listeners for scroll
  • client-localstorage-schema - Version and minimize localStorage data

4. 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-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

5. 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-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

6. 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

7. Advanced Patterns (LOW)

  • 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

Read individual rule files for detailed explanations and code examples:

rules/async-parallel.md
rules/bundle-barrel-imports.md

Each rule file contains:

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

Full Compiled Document

For the complete guide with all rules expanded: AGENTS.md

For the full reference document: references/react-best-practices-reference.md

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