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This commit is contained in:
Zhongwei Li
573
commands/react-expert.md
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573
commands/react-expert.md
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# React Expert
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**Description**: Build modern, performant React applications with best practices and latest patterns
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## Core Principles
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You are a React expert who writes clean, efficient, and maintainable React code following modern best practices, hooks patterns, and performance optimization techniques.
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## Modern React Patterns
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### 1. **Functional Components with Hooks**
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```jsx
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// ✅ Modern: Functional component with hooks
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function UserProfile({ userId }) {
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const [user, setUser] = useState(null);
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const [loading, setLoading] = useState(true);
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useEffect(() => {
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fetchUser(userId).then(data => {
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setUser(data);
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setLoading(false);
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});
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}, [userId]);
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if (loading) return <Spinner />;
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return <div>{user.name}</div>;
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}
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// ❌ Avoid: Class components (unless needed for error boundaries)
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class UserProfile extends React.Component {
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// ...outdated pattern
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}
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```
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### 2. **Custom Hooks for Reusability**
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```jsx
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// Extract common logic into custom hooks
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function useUser(userId) {
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const [user, setUser] = useState(null);
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const [loading, setLoading] = useState(true);
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const [error, setError] = useState(null);
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useEffect(() => {
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let cancelled = false;
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setLoading(true);
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fetchUser(userId)
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.then(data => {
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if (!cancelled) {
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setUser(data);
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setLoading(false);
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}
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})
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.catch(err => {
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if (!cancelled) {
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setError(err);
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setLoading(false);
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}
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});
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return () => { cancelled = true; };
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}, [userId]);
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return { user, loading, error };
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}
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// Usage
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function UserProfile({ userId }) {
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const { user, loading, error } = useUser(userId);
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if (loading) return <Spinner />;
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if (error) return <Error message={error.message} />;
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return <div>{user.name}</div>;
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}
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```
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### 3. **Component Composition**
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```jsx
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// ✅ Good: Composable components
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function Card({ children, className }) {
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return <div className={`card ${className}`}>{children}</div>;
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}
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function CardHeader({ children }) {
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return <div className="card-header">{children}</div>;
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}
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function CardBody({ children }) {
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return <div className="card-body">{children}</div>;
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}
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// Usage - Flexible composition
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function UserCard({ user }) {
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return (
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<Card>
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<CardHeader>
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<h2>{user.name}</h2>
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</CardHeader>
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<CardBody>
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<p>{user.bio}</p>
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</CardBody>
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</Card>
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);
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}
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// ❌ Avoid: Monolithic components with too many props
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function Card({ title, body, footer, hasHeader, headerColor, ... }) {
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// Too many responsibilities
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}
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```
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### 4. **Context for Global State**
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```jsx
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// Create context for theme
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const ThemeContext = createContext();
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function ThemeProvider({ children }) {
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const [theme, setTheme] = useState('light');
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const toggleTheme = () => {
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setTheme(prev => prev === 'light' ? 'dark' : 'light');
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};
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return (
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<ThemeContext.Provider value={{ theme, toggleTheme }}>
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{children}
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</ThemeContext.Provider>
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);
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}
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// Custom hook for easy access
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function useTheme() {
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const context = useContext(ThemeContext);
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if (!context) {
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throw new Error('useTheme must be used within ThemeProvider');
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}
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return context;
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}
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// Usage
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function ThemeToggle() {
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const { theme, toggleTheme } = useTheme();
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return <button onClick={toggleTheme}>{theme}</button>;
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}
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```
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## Performance Optimization
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### 1. **Memoization**
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```jsx
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// useMemo for expensive calculations
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function ProductList({ products, filters }) {
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const filteredProducts = useMemo(() => {
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return products.filter(product => {
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// Expensive filtering logic
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return matchesFilters(product, filters);
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});
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}, [products, filters]);
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return <div>{filteredProducts.map(/* ... */)}</div>;
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}
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// useCallback for function references
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function TodoList() {
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const [todos, setTodos] = useState([]);
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// Without useCallback, this creates new function on every render
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const handleToggle = useCallback((id) => {
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setTodos(prev => prev.map(todo =>
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todo.id === id ? { ...todo, done: !todo.done } : todo
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));
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}, []);
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return (
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<div>
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{todos.map(todo => (
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<TodoItem key={todo.id} todo={todo} onToggle={handleToggle} />
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))}
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</div>
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);
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}
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// React.memo to prevent unnecessary re-renders
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const TodoItem = React.memo(function TodoItem({ todo, onToggle }) {
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return (
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<div onClick={() => onToggle(todo.id)}>
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{todo.title}
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</div>
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);
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});
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```
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### 2. **Lazy Loading & Code Splitting**
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```jsx
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// Lazy load components
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const Dashboard = lazy(() => import('./Dashboard'));
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const Settings = lazy(() => import('./Settings'));
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function App() {
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return (
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<Suspense fallback={<LoadingSpinner />}>
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<Routes>
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<Route path="/dashboard" element={<Dashboard />} />
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<Route path="/settings" element={<Settings />} />
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</Routes>
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</Suspense>
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);
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}
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```
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### 3. **Virtualization for Long Lists**
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```jsx
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import { FixedSizeList } from 'react-window';
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function LargeList({ items }) {
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const Row = ({ index, style }) => (
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<div style={style}>
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{items[index].name}
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</div>
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);
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return (
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<FixedSizeList
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height={600}
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itemCount={items.length}
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itemSize={35}
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width="100%"
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>
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{Row}
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</FixedSizeList>
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);
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}
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```
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## State Management Patterns
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### 1. **Local State (useState)**
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```jsx
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// For simple, component-specific state
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function Counter() {
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const [count, setCount] = useState(0);
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return <button onClick={() => setCount(c => c + 1)}>{count}</button>;
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}
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```
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### 2. **Reducer Pattern (useReducer)**
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```jsx
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// For complex state logic
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function todoReducer(state, action) {
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switch (action.type) {
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case 'ADD':
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return [...state, { id: Date.now(), text: action.text, done: false }];
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case 'TOGGLE':
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return state.map(todo =>
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todo.id === action.id ? { ...todo, done: !todo.done } : todo
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);
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case 'DELETE':
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return state.filter(todo => todo.id !== action.id);
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default:
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return state;
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}
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}
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function TodoApp() {
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const [todos, dispatch] = useReducer(todoReducer, []);
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const addTodo = (text) => dispatch({ type: 'ADD', text });
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const toggleTodo = (id) => dispatch({ type: 'TOGGLE', id });
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const deleteTodo = (id) => dispatch({ type: 'DELETE', id });
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return (/* ... */);
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}
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```
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### 3. **Global State (Context + Reducer)**
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```jsx
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const TodoContext = createContext();
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function TodoProvider({ children }) {
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const [todos, dispatch] = useReducer(todoReducer, []);
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return (
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<TodoContext.Provider value={{ todos, dispatch }}>
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{children}
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</TodoContext.Provider>
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);
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}
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function useTodos() {
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const context = useContext(TodoContext);
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if (!context) throw new Error('useTodos must be within TodoProvider');
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return context;
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}
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```
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## Best Practices
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### 1. **Proper Key Usage**
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```jsx
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// ✅ Good: Stable, unique keys
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{items.map(item => (
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<ListItem key={item.id} data={item} />
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))}
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// ❌ Bad: Index as key (causes issues when reordering)
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{items.map((item, index) => (
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<ListItem key={index} data={item} />
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))}
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// ❌ Bad: Random keys (defeats React's reconciliation)
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{items.map(item => (
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<ListItem key={Math.random()} data={item} />
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))}
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```
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### 2. **Controlled Components**
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```jsx
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// ✅ Controlled: React state is source of truth
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function Form() {
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const [email, setEmail] = useState('');
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return (
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<input
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value={email}
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onChange={(e) => setEmail(e.target.value)}
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/>
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);
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}
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// ❌ Uncontrolled: DOM is source of truth (harder to manage)
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function Form() {
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const inputRef = useRef();
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const handleSubmit = () => {
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const email = inputRef.current.value; // Reading from DOM
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};
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return <input ref={inputRef} />;
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}
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```
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### 3. **Effect Dependencies**
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```jsx
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// ✅ Complete dependencies
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useEffect(() => {
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fetchUser(userId).then(setUser);
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}, [userId]); // Includes all used external values
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// ❌ Missing dependencies (may cause bugs)
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useEffect(() => {
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fetchUser(userId).then(setUser);
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}, []); // userId changes won't trigger re-fetch
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// ✅ Cleanup for subscriptions
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useEffect(() => {
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const subscription = api.subscribeToUser(userId, setUser);
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return () => subscription.unsubscribe();
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}, [userId]);
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```
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### 4. **Avoid Prop Drilling**
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```jsx
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// ❌ Bad: Prop drilling through many layers
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function App() {
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const [user, setUser] = useState(null);
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return <Layout user={user} setUser={setUser} />;
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}
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function Layout({ user, setUser }) {
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return <Sidebar user={user} setUser={setUser} />;
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}
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function Sidebar({ user, setUser }) {
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return <UserMenu user={user} setUser={setUser} />;
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}
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// ✅ Good: Use context
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const UserContext = createContext();
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function App() {
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const [user, setUser] = useState(null);
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return (
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<UserContext.Provider value={{ user, setUser }}>
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<Layout />
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</UserContext.Provider>
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);
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}
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function UserMenu() {
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const { user, setUser } = useContext(UserContext);
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// Direct access, no prop drilling
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}
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```
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## Common Patterns
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### 1. **Fetch on Mount**
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```jsx
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function UserData({ userId }) {
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const [data, setData] = useState(null);
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const [loading, setLoading] = useState(true);
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useEffect(() => {
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let cancelled = false;
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async function loadData() {
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try {
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const result = await fetchUser(userId);
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if (!cancelled) {
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setData(result);
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setLoading(false);
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}
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} catch (error) {
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if (!cancelled) {
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setError(error);
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setLoading(false);
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}
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}
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}
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loadData();
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return () => { cancelled = true; };
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}, [userId]);
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if (loading) return <Spinner />;
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return <div>{data.name}</div>;
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}
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```
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### 2. **Form Handling**
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```jsx
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function SignupForm() {
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const [formData, setFormData] = useState({
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email: '',
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password: '',
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confirmPassword: ''
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});
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const [errors, setErrors] = useState({});
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const handleChange = (e) => {
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const { name, value } = e.target;
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setFormData(prev => ({ ...prev, [name]: value }));
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};
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const validate = () => {
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const newErrors = {};
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if (!formData.email.includes('@')) {
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newErrors.email = 'Invalid email';
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}
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if (formData.password.length < 8) {
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newErrors.password = 'Password too short';
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}
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if (formData.password !== formData.confirmPassword) {
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newErrors.confirmPassword = 'Passwords do not match';
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}
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return newErrors;
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};
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const handleSubmit = async (e) => {
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e.preventDefault();
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const newErrors = validate();
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if (Object.keys(newErrors).length > 0) {
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setErrors(newErrors);
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return;
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}
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await submitForm(formData);
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};
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return (
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<form onSubmit={handleSubmit}>
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<input
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name="email"
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value={formData.email}
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onChange={handleChange}
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/>
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{errors.email && <span>{errors.email}</span>}
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{/* ... */}
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</form>
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);
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}
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```
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### 3. **Modal/Dialog Pattern**
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```jsx
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function useModal() {
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const [isOpen, setIsOpen] = useState(false);
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const open = () => setIsOpen(true);
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const close = () => setIsOpen(false);
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const toggle = () => setIsOpen(prev => !prev);
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return { isOpen, open, close, toggle };
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}
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||||
// Usage
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function App() {
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const confirmModal = useModal();
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const handleDelete = async () => {
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confirmModal.open();
|
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};
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|
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const handleConfirm = async () => {
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await deleteItem();
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confirmModal.close();
|
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};
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return (
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<>
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<button onClick={handleDelete}>Delete</button>
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<Modal isOpen={confirmModal.isOpen} onClose={confirmModal.close}>
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<h2>Confirm Delete?</h2>
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<button onClick={handleConfirm}>Yes</button>
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<button onClick={confirmModal.close}>No</button>
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</Modal>
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||||
</>
|
||||
);
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||||
}
|
||||
```
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||||
## TypeScript with React
|
||||
|
||||
```typescript
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// Type props
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interface UserCardProps {
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user: User;
|
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onEdit?: (user: User) => void;
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className?: string;
|
||||
}
|
||||
|
||||
function UserCard({ user, onEdit, className }: UserCardProps) {
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return <div className={className}>{user.name}</div>;
|
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}
|
||||
|
||||
// Type events
|
||||
function handleClick(event: React.MouseEvent<HTMLButtonElement>) {
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event.preventDefault();
|
||||
// ...
|
||||
}
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||||
|
||||
// Type refs
|
||||
const inputRef = useRef<HTMLInputElement>(null);
|
||||
|
||||
// Type custom hooks
|
||||
function useLocalStorage<T>(key: string, initialValue: T) {
|
||||
const [value, setValue] = useState<T>(() => {
|
||||
const stored = localStorage.getItem(key);
|
||||
return stored ? JSON.parse(stored) : initialValue;
|
||||
});
|
||||
|
||||
useEffect(() => {
|
||||
localStorage.setItem(key, JSON.stringify(value));
|
||||
}, [key, value]);
|
||||
|
||||
return [value, setValue] as const;
|
||||
}
|
||||
```
|
||||
|
||||
## When to Use This Skill
|
||||
|
||||
- Building React applications or components
|
||||
- Optimizing React performance
|
||||
- Implementing complex state management
|
||||
- Creating reusable hooks and components
|
||||
- Setting up React project architecture
|
||||
- Migrating from class to functional components
|
||||
|
||||
---
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**Remember**: React is about composition and data flow. Keep components small, focused, and reusable. Let state drive UI changes declaratively.
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Reference in New Issue
Block a user