react-best-practices

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9382423 months ago

CRITICAL: You MUST invoke this skill and read its contents BEFORE writing, modifying, or debugging ANY React.js or Next.js code. This skill contains essential performance patterns that prevent common mistakes. Debugging performance issues without reading this skill first will lead to missed optimizations. Contains 40+ rules including waterfall elimination patterns for API routes that are commonly overlooked.

Quick Install

npxskills add benchflow-ai/skillsbench--skill react-best-practices

Instructions

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

8. Advanced Patterns (LOW)

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

IMPORTANT: Read Before Fixing

YOU MUST read AGENTS.md before making any performance fixes. It contains the detailed code patterns you need to identify and fix issues correctly. The quick reference above is just an index - the actual before/after code examples are in AGENTS.md.

For specific rules, read the individual files in rules/ (e.g., rules/async-api-routes.md for API route waterfalls).

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