react-patterns
React 19 performance patterns and composition architecture for Vite + Cloudflare projects. 50+ rules ranked by impact — eliminating waterfalls, bundle optimisation, re-render prevention, composition over boolean props, server/client boundaries, and React 19 APIs. Use when writing, reviewing, or refactoring React components. Triggers: 'react patterns', 'react review', 'react performance', 'optimise components', 'react best practices', 'composition patterns', 'why is it slow', 'reduce re-renders', 'fix waterfall'.
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Install
Works with every agent the skills CLI supports.
npx skills add https://github.com/jezweb/claude-skills --skill react-patterns- 01
Install
Run the command in your project. The CLI asks which agents to install for.
- 02
Describe the task
Ask your agent for something this skill covers. It loads react-patterns automatically when relevant.
- 03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.
SKILL.md
The instructions your agent reads when the skill is triggered.
React Patterns
Performance and composition patterns for React 19 + Vite + Cloudflare Workers projects. Use as a checklist when writing new components, a review guide when auditing existing code, or a refactoring playbook when something feels slow or tangled.
Rules are ranked by impact. Fix CRITICAL issues before touching MEDIUM ones.
When to Apply
- Writing new React components or pages
- Reviewing code for performance issues
- Refactoring components with too many props or re-renders
- Debugging "why is this slow?" or "why does this re-render?"
- Building reusable component libraries
- Code review before merging
1. Eliminating Waterfalls (CRITICAL)
Sequential async calls where they could be parallel. The #1 performance killer.
| Pattern | Problem | Fix |
|---|---|---|
| Await in sequence | const a = await getA(); const b = await getB(); | const [a, b] = await Promise.all([getA(), getB()]); |
| Fetch in child | Parent renders, then child fetches, then grandchild fetches | Hoist fetches to the highest common ancestor, pass data down |
| Suspense cascade | Multiple Suspense boundaries that resolve sequentially | One Suspense boundary wrapping all async siblings |
| Await before branch | const data = await fetch(); if (condition) { use(data); } | Move await inside the branch — don't fetch what you might not use |
| Import then render | const Component = await import('./Heavy'); return <Component /> | Use React.lazy() + <Suspense> — renders fallback instantly |
How to find them: Search for await in components. Each await is a potential waterfall. If two awaits are independent, they should be parallel.
2. Bundle Size (CRITICAL)
Every KB the user downloads is a KB they wait for.
| Pattern | Problem | Fix |
|---|---|---|
| Barrel imports | import { Button } from '@/components' pulls the entire barrel file | import { Button } from '@/components/ui/button' — direct import |
| No code splitting | Heavy component loaded on every page | React.lazy(() => import('./HeavyComponent')) + <Suspense> |
| Third-party at load | Analytics/tracking loaded before the app renders | Load after hydration: useEffect(() => { import('./analytics') }, []) |
| Full library import | import _ from 'lodash' (70KB) | import debounce from 'lodash/debounce' (1KB) |
| Lucide tree-shaking | import * as Icons from 'lucide-react' (all icons) | Explicit map: import { Home, Settings } from 'lucide-react' |
| Duplicate React | Library bundles its own React → "Cannot read properties of null" | resolve.dedupe: ['react', 'react-dom'] in vite.config.ts |
How to find them: npx vite-bundle-visualizer — shows what's in your bundle.
3. Composition Architecture (HIGH)
How you structure components matters more than how you optimise them.
| Pattern | Problem | Fix |
|---|---|---|
| Boolean prop explosion | <Card isCompact isClickable showBorder hasIcon isLoading> | Explicit variants: <CompactCard>, <ClickableCard> |
| Compound components | Complex component with 15 props | Split into <Dialog>, <Dialog.Trigger>, <Dialog.Content> with shared context |
| renderX props | <Layout renderSidebar={...} renderHeader={...} renderFooter={...}> | Use children + named slots: <Layout><Sidebar /><Header /></Layout> |
| Lift state | Sibling components can't share state | Move state to parent or context provider |
| Provider implementation | Consumer code knows about state management internals | Provider exposes interface { state, actions, meta } — implementation hidden |
| Inline components | function Parent() { function Child() { ... } return <Child /> } | Define Child outside Parent — inline components remount on every render |
The test: If a component has more than 5 boolean props, it needs composition, not more props.
4. Re-render Prevention (MEDIUM)
Not all re-renders are bad. Only fix re-renders that cause visible jank or wasted computation.
| Pattern | Problem | Fix |
|---|---|---|
| Default object/array props | function Foo({ items = [] }) → new array ref every render | Hoist: const DEFAULT = []; function Foo({ items = DEFAULT }) |
| Derived state in effect | useEffect(() => setFiltered(items.filter(...)), [items]) | Derive during render: const filtered = useMemo(() => items.filter(...), [items]) |
| Object dependency | useEffect(() => {...}, [config]) fires every render if config is {} | Use primitive deps: useEffect(() => {...}, [config.id, config.type]) |
| Subscribe to unused state | Component reads { user, theme, settings } but only uses user | Split context or use selector: useSyncExternalStore |
| State for transient values | const [mouseX, setMouseX] = useState(0) on mousemove | Use useRef for values that change frequently but don't need re-render |
| Inline callback props | <Button onClick={() => doThing(id)} /> — new function every render | useCallback or functional setState: <Button onClick={handleClick} /> |
How to find them: React DevTools Profiler → "Why did this render?" or <React.StrictMode> double-renders in dev.
5. React 19 Specifics (MEDIUM)
Patterns that changed or are new in React 19.
| Pattern | Old (React 18) | New (React 19) |
|---|---|---|
| Form state | useFormState | useActionState — renamed |
| Ref forwarding | forwardRef((props, ref) => ...) | function Component({ ref, ...props }) — ref is a regular prop |
| Context | useContext(MyContext) | use(MyContext) — works in conditionals and loops |
| Pending UI | Manual loading state | useTransition + startTransition for non-urgent updates |
| Route-level lazy | Works with createBrowserRouter only | Still true — <Route lazy={...}> is silently ignored with <BrowserRouter> |
| Optimistic updates | Manual state management | useOptimistic hook |
| Metadata | Helmet or manual <head> management | <title>, <meta>, <link> in component JSX — hoisted to <head> automatically |
6. Rendering Performance (MEDIUM)
| Pattern | Problem | Fix |
|---|---|---|
| Layout shift on load | Content jumps when async data arrives | Skeleton screens matching final layout dimensions |
| Animate SVG directly | Janky SVG animation | Wrap in <div>, animate the div instead |
| Large list rendering | 1000+ items in a table/list | @tanstack/react-virtual for virtualised rendering |
| content-visibility | Long scrollable content renders everything upfront | content-visibility: auto on off-screen sections |
| Conditional render with && | {count && <Items />} renders 0 when count is 0 | Use ternary: {count > 0 ? <Items /> : null} |
7. Data Fetching (MEDIUM)
| Pattern | Problem | Fix |
|---|---|---|
| No deduplication | Same data fetched by 3 components | TanStack Query or SWR — automatic dedup + caching |
| Fetch on mount | useEffect(() => { fetch(...) }, []) — waterfalls, no caching, no dedup | TanStack Query: useQuery({ queryKey: ['users'], queryFn: fetchUsers }) |
| No optimistic update | User clicks save, waits 2 seconds, then sees change | useMutation with onMutate for instant visual feedback |
| Stale closure in interval | setInterval captures stale state | useRef for the interval ID and current values |
| Polling without cleanup | setInterval in useEffect without clearInterval | Return cleanup: useEffect(() => { const id = setInterval(...); return () => clearInterval(id); }) |
8. Vite + Cloudflare Specifics (MEDIUM)
| Pattern | Problem | Fix |
|---|---|---|
import.meta.env in Node scripts | Undefined — only works in Vite-processed files | Use loadEnv() from vite |
| React duplicate instance | Library bundles its own React | resolve.dedupe + optimizeDeps.include in vite.config.ts |
| Radix Select empty string | <SelectItem value=""> throws | Use sentinel: <SelectItem value="__any__"> |
| React Hook Form null | {...field} passes null to Input | Spread manually: value={field.value ?? ''} |
| Env vars at edge | process.env doesn't exist in Workers | Use c.env (Hono context) or import.meta.env (Vite build-time) |
Using as a Review Checklist
When reviewing code, go through categories 1-3 (CRITICAL + HIGH) for every PR. Categories 4-8 only when performance is a concern.
/react-patterns [file or component path]
Read the file, check against rules in priority order, report findings as:
file:line — [rule] description of issue
FAQ
What does the react-patterns skill do?
React 19 performance patterns and composition architecture for Vite + Cloudflare projects. 50+ rules ranked by impact — eliminating waterfalls, bundle optimisation, re-render prevention, composition over boolean props, server/client boundaries, and React 19 APIs. Use when writing, reviewing, or refactoring React components. Triggers: 'react patterns', 'react review', 'react performance', 'optimise components', 'react best practices', 'composition patterns', 'why is it slow', 'reduce re-renders', 'fix waterfall'.
How do I install react-patterns?
Run npx skills add https://github.com/jezweb/claude-skills --skill react-patterns in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/react-patterns/ (personal) or .claude/skills/react-patterns/ (project).
Which AI agents can use react-patterns?
Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.
Is react-patterns safe to install?
No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.
Who maintains react-patterns?
It is published by jezweb in jezweb/claude-skills. It has 1,291 recorded installs.
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