Vercel React Best Practices

⚠️ 性能提示: 此 Skill 包含 45 个 rules 文件（L1 ~50KB），专注于 React 性能优化。请根据实际场景选择性应用规则，优先处理 CRITICAL 和 HIGH 优先级的规则。

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.

动画性能规范（Animation Performance）

在 React 应用中实现高性能动画，遵循 compositor-only 原则。

核心原则

浏览器可以在 compositor thread 上独立于主线程处理两种属性：

• ✅ transform
• ✅ opacity

所有其他属性（width, height, top, left, background 等）必须在主线程上计算，可能导致卡顿。

只允许的属性

/* ✅ 允许：transform */
transform: translateX(100px);
transform: scale(1.1);
transform: rotate(45deg);
transform: skewX(10deg);

/* ✅ 允许：opacity */
opacity: 0;
opacity: 1;

禁止的属性

/* ❌ 禁止：布局属性 */
width: 100%;
height: 200px;
top: 0;
left: 0;
margin: 10px;
padding: 20px;

/* ❌ 禁止：可能触发布局的属性 */
background-color: red;
border: 1px solid black;
color: blue;

动画实现示例

// ❌ 不合规：使用 height 动画
function ExpandingBox() {
  const [isExpanded, setIsExpanded] = useState(false);

  return (
    <div
      style={{
        height: isExpanded ? '200px' : '50px',
        transition: 'height 0.3s ease'
      }}
    >
      内容
    </div>
  );
}

// ✅ 合规：使用 transform 和 max-height
function ExpandingBox() {
  const [isExpanded, setIsExpanded] = useState(false);

  return (
    <div
      style={{
        maxHeight: isExpanded ? '200px' : '50px',
        overflow: 'hidden',
        transition: 'max-height 0.3s ease'
      }}
    >
      内容
    </div>
  );
}

// ✅ 最佳：纯 transform
function ExpandingBox() {
  const [isExpanded, setIsExpanded] = useState(false);

  return (
    <button => setIsExpanded(!isExpanded)}>
      <span style={{
        transform: isExpanded ? 'rotate(180deg)' : 'rotate(0)',
        transition: 'transform 0.3s ease'
      }}>
        ▼
      </span>
      内容
    </button>
  );
}

React 动画库使用规范

Framer Motion / Motion

// ✅ 合规：使用 motion.div
import { motion } from 'framer-motion';

function AnimatedComponent() {
  return (
    <motion.div
      initial={{ opacity: 0, x: -100 }}
      animate={{ opacity: 1, x: 0 }}
      transition={{ duration: 0.5, ease: 'easeOut' }}
    >
      内容
    </motion.div>
  );
}

// ✅ 合规：使用 useTransform 限制属性
import { motion, useTransform } from 'framer-motion';

function ParallaxHeader() {
  const scrollY = useScroll();
  const y = useTransform(scrollY, [0, 500], [0, -200]);

  return (
    <motion.header style={{ y }}>
      内容
    </motion.header>
  );
}

Tailwind CSS 动画

// ✅ 合规：使用 transform
<div className="transform hover:scale-105 transition-transform duration-200">
  内容
</div>

// ❌ 不合规：使用 width/height
<div className="w-0 hover:w-full transition-all duration-300">
  内容
</div>

性能检查清单

必须遵守

• 只使用 transform 和 opacity 进行动画
• 所有动画元素有 will-change 提示
• 动画持续时间 ≤ 300ms（交互反馈）
• 使用 transform: translate3d() 启用 GPU 加速

必须实现

• 支持 prefers-reduced-motion
• 离开视口时暂停动画
• 动画不阻塞主线程

/* will-change 提示 */
.animated-element {
  will-change: transform, opacity;
}

/* prefers-reduced-motion 支持 */
@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }
}

// 暂停视口外动画
import { useInView } from 'framer-motion';

function LazyAnimation() {
  const ref = useRef(null);
  const isInView = useInView(ref, { once: true, margin: '-100px' });

  return (
    <motion.div
      ref={ref}
      initial={{ opacity: 0 }}
      animate={isInView ? { opacity: 1 } : { opacity: 0 }}
    >
      内容
    </motion.div>
  );
}

常见错误示例

// ❌ 错误 1：宽度动画
function Modal() {
  return (
    <div style={{
      width: isOpen ? '100%' : '0',
      transition: 'width 0.3s'
    }} />
  );
}

// ✅ 正确：使用 transform
function Modal() {
  return (
    <div style={{
      transform: isOpen ? 'scaleX(1)' : 'scaleX(0)',
      transformOrigin: 'left'
    }} />
  );
}

// ❌ 错误 2：颜色动画
function Button() {
  return (
    <button style={{
      backgroundColor: isHovered ? '#ff0000' : '#0000ff',
      transition: 'background-color 0.3s'
    }} />
  );
}

// ✅ 正确：使用 opacity 或绝对定位覆盖
function Button() {
  return (
    <button className="relative">
      <span className="bg-blue-500" />
      <span
        className="absolute inset-0 bg-red-500 opacity-0 hover:opacity-100 transition-opacity"
      />
    </button>
  );
}

// ❌ 错误 3：位置动画
function Draggable() {
  return (
    <div style={{
      top: y,
      left: x,
      transition: 'top 0.2s, left 0.2s'
    }} />
  );
}

// ✅ 正确：使用 transform
function Draggable() {
  return (
    <motion.div
      drag
      style={{ x, y }}
    />
  );
}

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
• Implementing animations or transitions

Rule Categories by Priority

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
• 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

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-barrel-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 the complete guide with all rules expanded: AGENTS.md