vercel-react-best-practices

Category: Development & Coding | Uploader: caorushizi | Downloads: 0 | Version: v1.0（Latest）

React and Next.js performance optimization guidelines from Vercel Engineering. This skill should be used when writing, reviewing, or refactoring React/Next.js code to ensure optimal performance patterns. Triggers on tasks involving React components, Next.js pages, data fetching, bundle optimization, or performance improvements.

Changelog: Source: GitHub https://github.com/caorushizi/mediago

Directory Structure

Current level: tree/master/.agents/skills/vercel-react-best-practices/

📁 rules/
- 📄 _sections.md 1.5 KB
- 📄 _template.md 633 B
- 📄 advanced-event-handler-refs.md 1.5 KB
- 📄 advanced-init-once.md 967 B
- 📄 advanced-use-latest.md 1.1 KB
- 📄 async-api-routes.md 1.1 KB
- 📄 async-cheap-condition-before-await.md 1.2 KB
- 📄 async-defer-await.md 2.2 KB
- 📄 async-dependencies.md 1.3 KB
- 📄 async-parallel.md 659 B
- 📄 async-suspense-boundaries.md 2.5 KB
- 📄 bundle-barrel-imports.md 2.7 KB
- 📄 bundle-conditional.md 966 B
- 📄 bundle-defer-third-party.md 928 B
- 📄 bundle-dynamic-imports.md 799 B
- 📄 bundle-preload.md 1.1 KB
- 📄 client-event-listeners.md 2.0 KB
- 📄 client-localstorage-schema.md 2.0 KB
- 📄 client-passive-event-listeners.md 1.6 KB
- 📄 client-swr-dedup.md 1.1 KB
- 📄 js-batch-dom-css.md 3.2 KB
- 📄 js-cache-function-results.md 1.9 KB
- 📄 js-cache-property-access.md 536 B
- 📄 js-cache-storage.md 1.6 KB
- 📄 js-combine-iterations.md 768 B
- 📄 js-early-exit.md 1.1 KB
- 📄 js-flatmap-filter.md 1.4 KB
- 📄 js-hoist-regexp.md 1.0 KB
- 📄 js-index-maps.md 850 B
- 📄 js-length-check-first.md 1.7 KB
- 📄 js-min-max-loop.md 2.2 KB
- 📄 js-request-idle-callback.md 2.6 KB
- 📄 js-set-map-lookups.md 532 B
- 📄 js-tosorted-immutable.md 1.7 KB
- 📄 rendering-activity.md 566 B
- 📄 rendering-animate-svg-wrapper.md 1.1 KB
- 📄 rendering-conditional-render.md 938 B
- 📄 rendering-content-visibility.md 818 B
- 📄 rendering-hoist-jsx.md 993 B
- 📄 rendering-hydration-no-flicker.md 2.2 KB
- 📄 rendering-hydration-suppress-warning.md 852 B
- 📄 rendering-resource-hints.md 2.6 KB
- 📄 rendering-script-defer-async.md 1.8 KB
- 📄 rendering-svg-precision.md 588 B
- 📄 rendering-usetransition-loading.md 2.0 KB
- 📄 rerender-defer-reads.md 983 B
- 📄 rerender-dependencies.md 833 B
- 📄 rerender-derived-state-no-effect.md 1.2 KB
- 📄 rerender-derived-state.md 732 B
- 📄 rerender-functional-setstate.md 2.9 KB
- 📄 rerender-lazy-state-init.md 2.0 KB
- 📄 rerender-memo-with-default-value.md 1.1 KB
- 📄 rerender-memo.md 1.1 KB
- 📄 rerender-move-effect-to-event.md 1.2 KB
- 📄 rerender-no-inline-components.md 2.1 KB
- 📄 rerender-simple-expression-in-memo.md 1023 B
- 📄 rerender-split-combined-hooks.md 1.8 KB
- 📄 rerender-transitions.md 1.0 KB
- 📄 rerender-use-deferred-value.md 1.8 KB
- 📄 rerender-use-ref-transient-values.md 1.7 KB
- 📄 server-after-nonblocking.md 2.0 KB
- 📄 server-auth-actions.md 2.6 KB
- 📄 server-cache-lru.md 1.3 KB
- 📄 server-cache-react.md 2.2 KB
- 📄 server-dedup-props.md 2.0 KB
- 📄 server-hoist-static-io.md 4.3 KB
- 📄 server-parallel-fetching.md 1.5 KB
- 📄 server-parallel-nested-fetching.md 1001 B
- 📄 server-serialization.md 1006 B
📄 AGENTS.md 100.2 KB
📄 README.md 3.3 KB
📄 SKILL.md 7.0 KB

SKILL.md

---
name: vercel-react-best-practices
description: React and Next.js performance optimization guidelines from Vercel Engineering. This skill should be used when writing, reviewing, or refactoring React/Next.js code to ensure optimal performance patterns. Triggers on tasks involving React components, Next.js pages, data fetching, bundle optimization, or performance improvements.
license: MIT
metadata:
  author: vercel
  version: "1.0.0"
---

# Vercel React Best Practices

Comprehensive performance optimization guide for React and Next.js applications, maintained by Vercel. Contains 67 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-cheap-condition-before-await` - Check cheap sync conditions before awaiting flags or remote values
- `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-auth-actions` - Authenticate server actions like API routes
- `server-cache-react` - Use React.cache() for per-request deduplication
- `server-cache-lru` - Use LRU cache for cross-request caching
- `server-dedup-props` - Avoid duplicate serialization in RSC props
- `server-hoist-static-io` - Hoist static I/O (fonts, logos) to module level
- `server-serialization` - Minimize data passed to client components
- `server-parallel-fetching` - Restructure components to parallelize fetches
- `server-parallel-nested-fetching` - Chain nested fetches per item in Promise.all
- `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
- `client-passive-event-listeners` - Use passive listeners for scroll
- `client-localstorage-schema` - Version and minimize localStorage data

### 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-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-split-combined-hooks` - Split hooks with independent dependencies
- `rerender-move-effect-to-event` - Put interaction logic in event handlers
- `rerender-transitions` - Use startTransition for non-urgent updates
- `rerender-use-deferred-value` - Defer expensive renders to keep input responsive
- `rerender-use-ref-transient-values` - Use refs for transient frequent values
- `rerender-no-inline-components` - Don't define components inside components

### 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-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
- `rendering-resource-hints` - Use React DOM resource hints for preloading
- `rendering-script-defer-async` - Use defer or async on script tags

### 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
- `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
- `js-flatmap-filter` - Use flatMap to map and filter in one pass
- `js-request-idle-callback` - Defer non-critical work to browser idle time

### 8. 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`

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