---
name: vercel-patterns
description: React composition and performance optimization patterns from Vercel. Use when building component libraries, refactoring components with prop proliferation, optimizing React/Next.js performance, or designing scalable component architectures. Covers composition patterns, React 19 APIs, performance optimization across waterfalls, bundle size, server/client rendering, and re-render optimization.
triggers:
  - vercel-patterns
  - patterns
---

# Vercel React Patterns

Composition patterns and performance optimization guidelines for building flexible, maintainable, and performant React and Next.js applications.

## When to Apply

Reference these guidelines when:

- Refactoring components with boolean prop proliferation
- Building reusable component libraries
- Designing flexible component APIs
- Reviewing component architecture
- Optimizing React/Next.js performance
- Implementing data fetching strategies
- Reducing bundle size or improving load times

## Component Composition Patterns

Avoid boolean prop proliferation by using compound components, lifting state, and composing internals. These patterns make codebases easier for both humans and AI agents to work with as they scale.

### 1. Component Architecture (HIGH PRIORITY)

- `architecture-avoid-boolean-props` - Don't add boolean props to customize behavior; use composition
- `architecture-compound-components` - Structure complex components with shared context

### 2. State Management (MEDIUM PRIORITY)

- `state-decouple-implementation` - Provider is the only place that knows how state is managed
- `state-context-interface` - Define generic interface with state, actions, meta for dependency injection
- `state-lift-state` - Move state into provider components for sibling access

### 3. Implementation Patterns (MEDIUM PRIORITY)

- `patterns-explicit-variants` - Create explicit variant components instead of boolean modes
- `patterns-children-over-render-props` - Use children for composition instead of renderX props

### 4. React 19 APIs (MEDIUM PRIORITY)

> **⚠️ React 19+ only.** Skip this section if using React 18 or earlier.

- `react19-no-forwardref` - Don't use `forwardRef`; use `use()` instead of `useContext()`

## Performance Optimization Patterns

Comprehensive performance optimization guide with 58 rules prioritized by impact.

### Priority 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

### Priority 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

### Priority 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-after-nonblocking` - Use after() for non-blocking operations

### Priority 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

### Priority 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-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

### Priority 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

### Priority 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

### Priority 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

For detailed explanations and code examples, reference individual pattern files:

```
rules/architecture-avoid-boolean-props.md
rules/async-parallel.md
rules/bundle-barrel-imports.md
rules/server-cache-react.md
```

Each pattern file contains:
- Brief explanation of why it matters
- Incorrect code example with explanation
- Correct code example with explanation
- Additional context and references

For the complete guide with all patterns expanded: `AGENTS.md`

## Quick Decision Tree

**Starting with components?** → Architecture patterns (compounds, state lifting, context)

**Optimizing waterfalls?** → Async patterns (parallel promises, Suspense, defer/await)

**Reducing bundle?** → Bundle patterns (dynamic imports, barrel avoidance, third-party deferral)

**Improving re-renders?** → Re-render patterns (memo, derived state, transitions)

## Outputs / Evidence

- Return the concrete deliverable, main decisions made, and any unresolved constraints
- Include which patterns were applied and the expected performance impact

## Failure / Stop Conditions

- Stop if key prerequisites are missing or the request changes scope enough that the current workflow no longer fits
- Do not bypass required gates or safeguards unless the user explicitly asks for it

## Memory Hooks

- Read memory when product, repo, or workflow history affects correctness
- Write memory only if this work establishes a durable policy or convention