React Best Practices

Comprehensive performance optimization guide for React and Next.js applications, tuned by gracefullight (forked from Vercel Engineering). Contains 42 rules across 8 categories (some rules are enforced by Biome linter), prioritized by impact to guide automated refactoring and code generation.

Project-Specific Notes

This project uses Orval + React Query (@tanstack/react-query) for API layer:

• Orval generates type-safe React Query hooks from OpenAPI specs

• Always use Orval-generated hooks in Client Components instead of RSC data fetching

• React Query handles caching, deduplication, and devtools

• RSC Components should handle layout, SEO metadata, and pass static props only

React Compiler is enabled (reactCompiler: true in next.config.ts):

• React Compiler automatically handles memoization (useMemo, useCallback, React.memo)

• Only use manual memoization when profiling a bottleneck or for genuinely expensive computations

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-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

Note: Barrel file imports are enforced by Biome linter (noBarrelFile , noReExportAll )

3. Server-Side Performance (HIGH)

• server-after-nonblocking
• Use after() for non-blocking operations

Note: RSC data fetching rules are excluded. This project uses Orval + React Query for API integration.

4. Client-Side Data Fetching (MEDIUM-HIGH)

• client-react-compiler-optimal

• React Compiler handles memoization, only use useMemo/useCallback when profiling bottlenecks

• client-orval-pattern

• Always use Orval-generated hooks for API data fetching

• client-tanstack-query-dedup

• Use @tanstack/query for automatic request deduplication

• client-event-listeners

• Deduplicate global event listeners

IMPORTANT: Do NOT use RSC async data fetching in this project. Use Orval-generated React Query hooks instead.

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

Note: Conditional rendering with && is enforced by Biome linter (noLeakedRender )

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-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

Note: RegExp hoisting is enforced by Biome linter (useTopLevelRegex )

8. Advanced Patterns (LOW)

• advanced-event-handler-refs

• Store event handlers in refs

• 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-dynamic-imports.md rules/_sections.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 complete guide with all rules expanded: AGENTS.md