React development

React Development

Build production-grade React with proper architecture, optimized hooks, and quality auditing.

When to Use This Skill

• Building React applications, component libraries, and client-side UI flows
• Creating reusable component libraries with shadcn/ui or fpkit
• Optimizing React hooks usage and eliminating anti-patterns
• Auditing React codebase quality with Bulletproof React
• Implementing accessible, well-tested components

When NOT to Use This Skill

• Next.js routing, SSR, server components → use nextjs-development
• CSS design systems, Tailwind utilities, accessibility patterns → use frontend-design
• Backend API development → use api-design or typescript-development
• Test framework setup → use testing-framework

---

Decision Tree

What are you building?
|
+-- React application or feature area?
|   --> Component/State Architecture (Section 1)
|
+-- Component library?
|   +-- shadcn/ui? --> CVA Variants + Radix Primitives (Section 2)
|   +-- fpkit? --> Composition Patterns (references/extended-patterns.md)
|
+-- Optimizing existing React code?
|   +-- Hooks issues (re-renders, stale state, dependency arrays)?
|   |   --> Anti-pattern Detection + Fix (Section 3)
|   +-- Code quality audit needed?
|       --> Bulletproof React Auditor (references/extended-patterns.md)
|
+-- Debugging a specific hooks problem?
    +-- Effect fires too often? --> Check dependency array (Section 3)
    +-- State stale in callback? --> Functional update or useRef
    +-- Component re-renders unnecessarily? --> Memoization decision tree

---

Section 1: React Application Architecture

Use this section for React-side organization: components, hooks, state, and client data access. If the work involves Next.js routing, Server Components, Server Actions, cache behavior, or SSR boundaries, switch to nextjs-development.

4-Layer Client Architecture

Types --> Services --> Hooks --> Components

src/
  types/           # TypeScript interfaces (database.types.ts)
  services/        # Client-safe API wrappers (users.service.ts)
  hooks/           # Client-side data hooks (use-users.ts)
  components/      # UI components (user-card.tsx)
  pages/ or routes/ # Framework-specific route integration, if present

Key Patterns

Services Layer (client-safe API wrapper):

// services/users.service.ts
export interface User {
  id: string
  name: string
}

export async function getUsers() {
  const response = await fetch('/api/users')
  if (!response.ok) throw new Error('Failed to load users')
  return response.json() as Promise<User[]>
}

Hooks Layer (Client-side):

// hooks/use-users.ts
import { useQuery } from '@tanstack/react-query'
import { getUsers } from '@/services/users.service'

export function useUsers() {
  return useQuery({
    queryKey: ['users'],
    queryFn: getUsers
  })
}

---

Section 2: shadcn/ui Component Architecture

CVA Variants Pattern

import { cva, type VariantProps } from 'class-variance-authority'

const buttonVariants = cva(
  'inline-flex items-center justify-center rounded-md text-sm font-medium',
  {
    variants: {
      variant: {
        default: 'bg-primary text-primary-foreground',
        secondary: 'bg-secondary text-secondary-foreground',
        outline: 'border border-input bg-background',
      },
      size: {
        default: 'h-10 px-4 py-2',
        sm: 'h-9 rounded-md px-3',
        lg: 'h-11 rounded-md px-8',
      },
    },
    defaultVariants: { variant: 'default', size: 'default' },
  }
)

Scripts

• scripts/shadcn-setup-tailwind.py - Generate Tailwind config with shadcn defaults
• scripts/shadcn-generate-component.py - Scaffold new shadcn-style components

---

Section 3: React Hooks Best Practices

Core Principle

"The best hook is the one you don't need to write."

Anti-Patterns with Solutions

1. Derived State — Don't use useState + useEffect for derived values.

// ANTI-PATTERN: derived state in useState+useEffect
const [searchQuery, setSearchQuery] = useState('');
const [filteredItems, setFilteredItems] = useState(items);
useEffect(() => {
  setFilteredItems(items.filter(item => item.name.includes(searchQuery)));
}, [searchQuery, items]); // extra re-render, stale data risk

// CORRECT: compute during render
const [searchQuery, setSearchQuery] = useState('');
const filteredItems = items.filter(item => item.name.includes(searchQuery));

2. Event Response — Don't use useEffect for user actions.

// ANTI-PATTERN: responding to events in useEffect
const [userId, setUserId] = useState(null);
useEffect(() => {
  if (userId) api.trackUserSelection(userId); // fires on every userId change
}, [userId]);

// CORRECT: handle in event handler
<Button onClick={() => {
  setUserId(id);
  api.trackUserSelection(id);
}}>Select</Button>

3. Props-to-State Sync — Don't mirror props in state.

// ANTI-PATTERN: syncing props to state
const [localValue, setLocalValue] = useState(props.value);
useEffect(() => { setLocalValue(props.value); }, [props.value]);

// CORRECT: use key prop for reset, or compute from props
<Editor key={props.documentId} initialValue={props.value} />

4. Premature Memoization — Don't useMemo/useCallback cheap operations.

// ANTI-PATTERN: memoizing cheap computations
const fullName = useMemo(() => `${first} ${last}`, [first, last]);

// CORRECT: compute during render (string concat is trivial)
const fullName = `${first} ${last}`;

When to Use Memoization

Only use useMemo/useCallback when:

1. Expensive computation (O(n log n) or worse)
2. Callback passed to memoized child component
3. Value used in dependency array of other hooks

Dependency Array Rules

1. Include all reactive values used inside the effect
2. Use functional updates to avoid state dependencies
3. Use refs for values that shouldn't trigger re-runs
4. Never suppress ESLint exhaustive-deps warnings

---

Best Practices Summary

Do

• Separate API services, hooks, and presentation components
• Calculate derived values during render (not in effects)
• Handle user actions in event handlers
• Use React Query/SWR for server state
• Keep components < 300 lines
• Use CSS variables for theming
• Follow accessibility patterns (WCAG 2.1 AA)

Don't

• Store derived state with useState + useEffect
• Use useEffect for event responses
• Sync props to state (use key for reset)
• Prematurely memoize cheap operations
• Suppress ESLint exhaustive-deps warnings
• Create components with > 10 props
• Skip keyboard accessibility

See Extended Patterns for fpkit component development, Bulletproof React auditing, detailed hooks anti-patterns, templates, and complete file reference.

---

Resources

• Next.js Documentation
• shadcn/ui
• fpkit Repository
• Bulletproof React
• React Docs - Rules of Hooks
• TanStack Query
• WCAG 2.1 Guidelines