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React Essentials

Essential React concepts for building modern user interfaces with components, hooks, and state management

March 10, 2024
•
Updated regularly

React Essentials

Quick reference guide for React - a JavaScript library for building user interfaces.

What is React?

React is a JavaScript library developed by Facebook for building UIs:

  • Component-Based - Build encapsulated components
  • Declarative - Design views for each state
  • Learn Once, Write Anywhere - Develop web, mobile, desktop apps
  • Virtual DOM - Efficient updates and rendering
  • Unidirectional Data Flow - Predictable state management
  • Rich Ecosystem - Thousands of libraries and tools
  • Strong Community - Wide adoption and support

    • Installation

    Create React App

    # ========== Create New Project ==========
npx create-react-app my-app

# With TypeScript
npx create-react-app my-app --template typescript

# ========== Start Development Server ==========
cd my-app
npm start

# Open http://localhost:3000

    # ========== Create New Project ==========
npm create vite@latest my-app -- --template react

# With TypeScript
npm create vite@latest my-app -- --template react-ts

# ========== Install and Run ==========
cd my-app
npm install
npm run dev

    Manual Setup

    # ========== Install React ==========
npm install react react-dom

# For TypeScript
npm install --save-dev @types/react @types/react-dom

    Components

    Function Components

    // ========== Basic Function Component ==========
function Welcome() {
  return <h1>Hello, World!</h1>;
}

// ========== With Props ==========
function Welcome(props) {
  return <h1>Hello, {props.name}!</h1>;
}

// Usage
<Welcome name="Alice" />

// ========== With Destructuring ==========
function Welcome({ name, age }) {
  return (
    <div>
      <h1>Hello, {name}!</h1>
      <p>Age: {age}</p>
    </div>
  );
}

// ========== TypeScript ==========
interface WelcomeProps {
  name: string;
  age: number;
}

function Welcome({ name, age }: WelcomeProps) {
  return (
    <div>
      <h1>Hello, {name}!</h1>
      <p>Age: {age}</p>
    </div>
  );
}

// ========== With Default Props ==========
function Welcome({ name = 'Guest', age = 0 }) {
  return <h1>Hello, {name}!</h1>;
}

// ========== Arrow Function ==========
const Welcome = ({ name }) => {
  return <h1>Hello, {name}!</h1>;
};

// Short form
const Welcome = ({ name }) => <h1>Hello, {name}!</h1>;

    Class Components (Legacy)

    // ========== Basic Class Component ==========
import React, { Component } from 'react';

class Welcome extends Component {
  render() {
    return <h1>Hello, {this.props.name}!</h1>;
  }
}

// ========== With State ==========
class Counter extends Component {
  constructor(props) {
    super(props);
    this.state = { count: 0 };
  }
  
  increment = () => {
    this.setState({ count: this.state.count + 1 });
  };
  
  render() {
    return (
      <div>
        <p>Count: {this.state.count}</p>
        <button onClick={this.increment}>Increment</button>
      </div>
    );
  }
}

// ========== Lifecycle Methods ==========
class UserProfile extends Component {
  componentDidMount() {
    // Called after component is mounted
    console.log('Component mounted');
  }
  
  componentDidUpdate(prevProps, prevState) {
    // Called after component updates
    console.log('Component updated');
  }
  
  componentWillUnmount() {
    // Called before component is unmounted
    console.log('Component will unmount');
  }
  
  render() {
    return <div>Profile</div>;
  }
}

    JSX

    Basic Syntax

    // ========== JavaScript Expressions ==========
const name = 'Alice';
const element = <h1>Hello, {name}!</h1>;

const user = { name: 'Bob', age: 30 };
const element = <h1>Hello, {user.name}!</h1>;

// ========== Attributes ==========
const element = <img src={imageUrl} alt="Description" />;
const element = <div className="container">Content</div>;
const element = <button onClick={handleClick}>Click me</button>;

// ========== Inline Styles ==========
const element = (
  <div style={{ color: 'red', fontSize: '20px' }}>
    Styled text
  </div>
);

// ========== Children ==========
const element = (
  <div>
    <h1>Title</h1>
    <p>Paragraph</p>
  </div>
);

// ========== Conditional Rendering ==========
const element = (
  <div>
    {isLoggedIn ? <UserGreeting /> : <GuestGreeting />}
  </div>
);

// Short circuit
const element = (
  <div>
    {isLoggedIn && <UserGreeting />}
  </div>
);

// ========== Lists ==========
const items = ['Apple', 'Banana', 'Orange'];
const element = (
  <ul>
    {items.map((item, index) => (
      <li key={index}>{item}</li>
    ))}
  </ul>
);

// ========== Fragments ==========
const element = (
  <>
    <h1>Title</h1>
    <p>Paragraph</p>
  </>
);

// Or
const element = (
  <React.Fragment>
    <h1>Title</h1>
    <p>Paragraph</p>
  </React.Fragment>
);

    Hooks

    useState

    // ========== Basic State ==========
import { useState } from 'react';

function Counter() {
  const [count, setCount] = useState(0);
  
  return (
    <div>
      <p>Count: {count}</p>
      <button onClick={() => setCount(count + 1)}>Increment</button>
      <button onClick={() => setCount(count - 1)}>Decrement</button>
      <button onClick={() => setCount(0)}>Reset</button>
    </div>
  );
}

// ========== Multiple State Variables ==========
function Form() {
  const [name, setName] = useState('');
  const [email, setEmail] = useState('');
  const [age, setAge] = useState(0);
  
  return (
    <form>
      <input value={name} onChange={(e) => setName(e.target.value)} />
      <input value={email} onChange={(e) => setEmail(e.target.value)} />
      <input value={age} onChange={(e) => setAge(Number(e.target.value))} />
    </form>
  );
}

// ========== Object State ==========
function UserProfile() {
  const [user, setUser] = useState({
    name: '',
    email: '',
    age: 0
  });
  
  const updateName = (name) => {
    setUser({ ...user, name });
  };
  
  const updateEmail = (email) => {
    setUser((prevUser) => ({ ...prevUser, email }));
  };
  
  return <div>{user.name}</div>;
}

// ========== Array State ==========
function TodoList() {
  const [todos, setTodos] = useState([]);
  
  const addTodo = (text) => {
    setTodos([...todos, { id: Date.now(), text }]);
  };
  
  const removeTodo = (id) => {
    setTodos(todos.filter(todo => todo.id !== id));
  };
  
  const updateTodo = (id, newText) => {
    setTodos(todos.map(todo => 
      todo.id === id ? { ...todo, text: newText } : todo
    ));
  };
  
  return (
    <ul>
      {todos.map(todo => (
        <li key={todo.id}>{todo.text}</li>
      ))}
    </ul>
  );
}

// ========== Lazy Initialization ==========
function ExpensiveComponent() {
  const [data, setData] = useState(() => {
    // Only runs on initial render
    return computeExpensiveValue();
  });
  
  return <div>{data}</div>;
}

    useEffect

    // ========== Basic Effect ==========
import { useEffect } from 'react';

function Example() {
  useEffect(() => {
    // Runs after every render
    console.log('Component rendered');
  });
  
  return <div>Example</div>;
}

// ========== Effect with Dependencies ==========
function User({ userId }) {
  const [user, setUser] = useState(null);
  
  useEffect(() => {
    // Runs when userId changes
    fetch(`/api/users/${userId}`)
      .then(res => res.json())
      .then(data => setUser(data));
  }, [userId]);
  
  return <div>{user?.name}</div>;
}

// ========== Effect with Cleanup ==========
function Timer() {
  const [count, setCount] = useState(0);
  
  useEffect(() => {
    const interval = setInterval(() => {
      setCount(c => c + 1);
    }, 1000);
    
    // Cleanup function
    return () => clearInterval(interval);
  }, []);
  
  return <div>Count: {count}</div>;
}

// ========== Run Once (Component Mount) ==========
function DataFetcher() {
  const [data, setData] = useState(null);
  
  useEffect(() => {
    // Only runs once on mount
    fetchData().then(setData);
  }, []);
  
  return <div>{data}</div>;
}

// ========== Multiple Effects ==========
function Component() {
  useEffect(() => {
    // Effect 1: Data fetching
    fetchData();
  }, []);
  
  useEffect(() => {
    // Effect 2: Event listener
    window.addEventListener('resize', handleResize);
    return () => window.removeEventListener('resize', handleResize);
  }, []);
  
  useEffect(() => {
    // Effect 3: Document title
    document.title = `Count: ${count}`;
  }, [count]);
  
  return <div>Component</div>;
}

    useContext

    // ========== Create Context ==========
import { createContext, useContext, useState } from 'react';

const ThemeContext = createContext();

// ========== Provider Component ==========
function ThemeProvider({ children }) {
  const [theme, setTheme] = useState('light');
  
  const toggleTheme = () => {
    setTheme(theme === 'light' ? 'dark' : 'light');
  };
  
  return (
    <ThemeContext.Provider value={{ theme, toggleTheme }}>
      {children}
    </ThemeContext.Provider>
  );
}

// ========== Consumer Component ==========
function ThemedButton() {
  const { theme, toggleTheme } = useContext(ThemeContext);
  
  return (
    <button 
      onClick={toggleTheme}
      style={{ 
        background: theme === 'light' ? '#fff' : '#333',
        color: theme === 'light' ? '#333' : '#fff'
      }}
    >
      Toggle Theme
    </button>
  );
}

// ========== App ==========
function App() {
  return (
    <ThemeProvider>
      <ThemedButton />
    </ThemeProvider>
  );
}

// ========== Auth Context Example ==========
const AuthContext = createContext();

function AuthProvider({ children }) {
  const [user, setUser] = useState(null);
  
  const login = async (email, password) => {
    const user = await api.login(email, password);
    setUser(user);
  };
  
  const logout = () => {
    setUser(null);
  };
  
  return (
    <AuthContext.Provider value={{ user, login, logout }}>
      {children}
    </AuthContext.Provider>
  );
}

function useAuth() {
  const context = useContext(AuthContext);
  if (!context) {
    throw new Error('useAuth must be used within AuthProvider');
  }
  return context;
}

    useReducer

    // ========== Basic Reducer ==========
import { useReducer } from 'react';

function reducer(state, action) {
  switch (action.type) {
    case 'increment':
      return { count: state.count + 1 };
    case 'decrement':
      return { count: state.count - 1 };
    case 'reset':
      return { count: 0 };
    default:
      throw new Error('Unknown action');
  }
}

function Counter() {
  const [state, dispatch] = useReducer(reducer, { count: 0 });
  
  return (
    <div>
      <p>Count: {state.count}</p>
      <button onClick={() => dispatch({ type: 'increment' })}>+</button>
      <button onClick={() => dispatch({ type: 'decrement' })}>-</button>
      <button onClick={() => dispatch({ type: 'reset' })}>Reset</button>
    </div>
  );
}

// ========== Complex State Management ==========
const initialState = {
  todos: [],
  filter: 'all'
};

function todoReducer(state, action) {
  switch (action.type) {
    case 'ADD_TODO':
      return {
        ...state,
        todos: [...state.todos, action.payload]
      };
    case 'REMOVE_TODO':
      return {
        ...state,
        todos: state.todos.filter(todo => todo.id !== action.payload)
      };
    case 'TOGGLE_TODO':
      return {
        ...state,
        todos: state.todos.map(todo =>
          todo.id === action.payload
            ? { ...todo, completed: !todo.completed }
            : todo
        )
      };
    case 'SET_FILTER':
      return {
        ...state,
        filter: action.payload
      };
    default:
      return state;
  }
}

function TodoApp() {
  const [state, dispatch] = useReducer(todoReducer, initialState);
  
  const addTodo = (text) => {
    dispatch({
      type: 'ADD_TODO',
      payload: { id: Date.now(), text, completed: false }
    });
  };
  
  return <div>Todo App</div>;
}

    useRef

    // ========== DOM Reference ==========
import { useRef, useEffect } from 'react';

function TextInput() {
  const inputRef = useRef(null);
  
  useEffect(() => {
    // Focus input on mount
    inputRef.current.focus();
  }, []);
  
  return <input ref={inputRef} />;
}

// ========== Previous Value ==========
function Counter() {
  const [count, setCount] = useState(0);
  const prevCountRef = useRef();
  
  useEffect(() => {
    prevCountRef.current = count;
  }, [count]);
  
  const prevCount = prevCountRef.current;
  
  return (
    <div>
      <p>Current: {count}</p>
      <p>Previous: {prevCount}</p>
      <button onClick={() => setCount(count + 1)}>Increment</button>
    </div>
  );
}

// ========== Mutable Value ==========
function Timer() {
  const [count, setCount] = useState(0);
  const intervalRef = useRef();
  
  const start = () => {
    if (intervalRef.current) return;
    intervalRef.current = setInterval(() => {
      setCount(c => c + 1);
    }, 1000);
  };
  
  const stop = () => {
    clearInterval(intervalRef.current);
    intervalRef.current = null;
  };
  
  return (
    <div>
      <p>Count: {count}</p>
      <button onClick={start}>Start</button>
      <button onClick={stop}>Stop</button>
    </div>
  );
}

    useMemo

    // ========== Expensive Computation ==========
import { useMemo } from 'react';

function ExpensiveComponent({ items }) {
  const sortedItems = useMemo(() => {
    console.log('Sorting items...');
    return items.sort((a, b) => a.value - b.value);
  }, [items]);
  
  return (
    <ul>
      {sortedItems.map(item => (
        <li key={item.id}>{item.value}</li>
      ))}
    </ul>
  );
}

// ========== Derived State ==========
function UserList({ users, searchQuery }) {
  const filteredUsers = useMemo(() => {
    return users.filter(user =>
      user.name.toLowerCase().includes(searchQuery.toLowerCase())
    );
  }, [users, searchQuery]);
  
  return (
    <ul>
      {filteredUsers.map(user => (
        <li key={user.id}>{user.name}</li>
      ))}
    </ul>
  );
}

    useCallback

    // ========== Prevent Unnecessary Re-renders ==========
import { useCallback } from 'react';

function Parent() {
  const [count, setCount] = useState(0);
  const [text, setText] = useState('');
  
  // Without useCallback, new function on every render
  const handleClick = useCallback(() => {
    console.log('Button clicked');
  }, []);
  
  return (
    <div>
      <input value={text} onChange={(e) => setText(e.target.value)} />
      <Child onClick={handleClick} />
    </div>
  );
}

const Child = React.memo(({ onClick }) => {
  console.log('Child rendered');
  return <button onClick={onClick}>Click me</button>;
});

// ========== With Dependencies ==========
function SearchComponent() {
  const [query, setQuery] = useState('');
  
  const handleSearch = useCallback((value) => {
    console.log('Searching for:', value);
    api.search(query, value);
  }, [query]);
  
  return <SearchInput onSearch={handleSearch} />;
}

    Custom Hooks

    // ========== useFetch Hook ==========
function useFetch(url) {
  const [data, setData] = useState(null);
  const [loading, setLoading] = useState(true);
  const [error, setError] = useState(null);
  
  useEffect(() => {
    setLoading(true);
    fetch(url)
      .then(res => res.json())
      .then(data => {
        setData(data);
        setLoading(false);
      })
      .catch(err => {
        setError(err);
        setLoading(false);
      });
  }, [url]);
  
  return { data, loading, error };
}

// Usage
function Users() {
  const { data, loading, error } = useFetch('/api/users');
  
  if (loading) return <div>Loading...</div>;
  if (error) return <div>Error: {error.message}</div>;
  
  return (
    <ul>
      {data.map(user => (
        <li key={user.id}>{user.name}</li>
      ))}
    </ul>
  );
}

// ========== useLocalStorage Hook ==========
function useLocalStorage(key, initialValue) {
  const [value, setValue] = useState(() => {
    const item = localStorage.getItem(key);
    return item ? JSON.parse(item) : initialValue;
  });
  
  useEffect(() => {
    localStorage.setItem(key, JSON.stringify(value));
  }, [key, value]);
  
  return [value, setValue];
}

// Usage
function Settings() {
  const [theme, setTheme] = useLocalStorage('theme', 'light');
  
  return (
    <button onClick={() => setTheme(theme === 'light' ? 'dark' : 'light')}>
      Current theme: {theme}
    </button>
  );
}

// ========== useDebounce Hook ==========
function useDebounce(value, delay) {
  const [debouncedValue, setDebouncedValue] = useState(value);
  
  useEffect(() => {
    const handler = setTimeout(() => {
      setDebouncedValue(value);
    }, delay);
    
    return () => clearTimeout(handler);
  }, [value, delay]);
  
  return debouncedValue;
}

// Usage
function SearchBox() {
  const [query, setQuery] = useState('');
  const debouncedQuery = useDebounce(query, 500);
  
  useEffect(() => {
    if (debouncedQuery) {
      api.search(debouncedQuery);
    }
  }, [debouncedQuery]);
  
  return <input value={query} onChange={(e) => setQuery(e.target.value)} />;
}

    Forms

    Controlled Components

    // ========== Simple Form ==========
function LoginForm() {
  const [email, setEmail] = useState('');
  const [password, setPassword] = useState('');
  
  const handleSubmit = (e) => {
    e.preventDefault();
    console.log('Login:', { email, password });
  };
  
  return (
    <form onSubmit={handleSubmit}>
      <input
        type="email"
        value={email}
        onChange={(e) => setEmail(e.target.value)}
        placeholder="Email"
      />
      <input
        type="password"
        value={password}
        onChange={(e) => setPassword(e.target.value)}
        placeholder="Password"
      />
      <button type="submit">Login</button>
    </form>
  );
}

// ========== Complex Form ==========
function RegistrationForm() {
  const [formData, setFormData] = useState({
    name: '',
    email: '',
    password: '',
    country: '',
    terms: false
  });
  
  const handleChange = (e) => {
    const { name, value, type, checked } = e.target;
    setFormData(prev => ({
      ...prev,
      [name]: type === 'checkbox' ? checked : value
    }));
  };
  
  const handleSubmit = (e) => {
    e.preventDefault();
    console.log('Form data:', formData);
  };
  
  return (
    <form onSubmit={handleSubmit}>
      <input
        name="name"
        value={formData.name}
        onChange={handleChange}
        placeholder="Name"
      />
      <input
        name="email"
        type="email"
        value={formData.email}
        onChange={handleChange}
        placeholder="Email"
      />
      <input
        name="password"
        type="password"
        value={formData.password}
        onChange={handleChange}
        placeholder="Password"
      />
      <select name="country" value={formData.country} onChange={handleChange}>
        <option value="">Select country</option>
        <option value="us">United States</option>
        <option value="uk">United Kingdom</option>
      </select>
      <label>
        <input
          name="terms"
          type="checkbox"
          checked={formData.terms}
          onChange={handleChange}
        />
        Accept terms
      </label>
      <button type="submit">Register</button>
    </form>
  );
}

    Form Validation

    // ========== With Validation ==========
function ValidatedForm() {
  const [email, setEmail] = useState('');
  const [password, setPassword] = useState('');
  const [errors, setErrors] = useState({});
  
  const validate = () => {
    const newErrors = {};
    
    if (!email) {
      newErrors.email = 'Email is required';
    } else if (!/\S+@\S+\.\S+/.test(email)) {
      newErrors.email = 'Email is invalid';
    }
    
    if (!password) {
      newErrors.password = 'Password is required';
    } else if (password.length < 8) {
      newErrors.password = 'Password must be at least 8 characters';
    }
    
    return newErrors;
  };
  
  const handleSubmit = (e) => {
    e.preventDefault();
    
    const validationErrors = validate();
    if (Object.keys(validationErrors).length > 0) {
      setErrors(validationErrors);
      return;
    }
    
    // Submit form
    console.log('Form submitted');
    setErrors({});
  };
  
  return (
    <form onSubmit={handleSubmit}>
      <div>
        <input
          type="email"
          value={email}
          onChange={(e) => setEmail(e.target.value)}
          placeholder="Email"
        />
        {errors.email && <span className="error">{errors.email}</span>}
      </div>
      <div>
        <input
          type="password"
          value={password}
          onChange={(e) => setPassword(e.target.value)}
          placeholder="Password"
        />
        {errors.password && <span className="error">{errors.password}</span>}
      </div>
      <button type="submit">Submit</button>
    </form>
  );
}

    Performance Optimization

    React.memo

    // ========== Prevent Re-renders ==========
const ExpensiveComponent = React.memo(function ExpensiveComponent({ data }) {
  console.log('Rendering ExpensiveComponent');
  return <div>{data}</div>;
});

// ========== With Custom Comparison ==========
const UserCard = React.memo(
  function UserCard({ user }) {
    return <div>{user.name}</div>;
  },
  (prevProps, nextProps) => {
    // Return true if props are equal (skip re-render)
    return prevProps.user.id === nextProps.user.id;
  }
);

    Code Splitting

    // ========== Lazy Loading ==========
import { lazy, Suspense } from 'react';

const HeavyComponent = lazy(() => import('./HeavyComponent'));

function App() {
  return (
    <Suspense fallback={<div>Loading...</div>}>
      <HeavyComponent />
    </Suspense>
  );
}

// ========== Route-based Splitting ==========
const Home = lazy(() => import('./pages/Home'));
const About = lazy(() => import('./pages/About'));
const Contact = lazy(() => import('./pages/Contact'));

function App() {
  return (
    <Suspense fallback={<LoadingSpinner />}>
      <Routes>
        <Route path="/" element={<Home />} />
        <Route path="/about" element={<About />} />
        <Route path="/contact" element={<Contact />} />
      </Routes>
    </Suspense>
  );
}

    Error Handling

    Error Boundaries

    // ========== Error Boundary Component ==========
class ErrorBoundary extends React.Component {
  constructor(props) {
    super(props);
    this.state = { hasError: false, error: null };
  }
  
  static getDerivedStateFromError(error) {
    return { hasError: true, error };
  }
  
  componentDidCatch(error, errorInfo) {
    console.error('Error caught:', error, errorInfo);
    // Log to error reporting service
  }
  
  render() {
    if (this.state.hasError) {
      return (
        <div>
          <h1>Something went wrong</h1>
          <p>{this.state.error?.message}</p>
        </div>
      );
    }
    
    return this.props.children;
  }
}

// Usage
function App() {
  return (
    <ErrorBoundary>
      <MyComponent />
    </ErrorBoundary>
  );
}

    Common Patterns

    Container/Presentational Pattern

    // ========== Presentational Component ==========
function UserList({ users, onUserClick }) {
  return (
    <ul>
      {users.map(user => (
        <li key={user.id} onClick={() => onUserClick(user)}>
          {user.name}
        </li>
      ))}
    </ul>
  );
}

// ========== Container Component ==========
function UserListContainer() {
  const [users, setUsers] = useState([]);
  const [loading, setLoading] = useState(true);
  
  useEffect(() => {
    fetchUsers().then(data => {
      setUsers(data);
      setLoading(false);
    });
  }, []);
  
  const handleUserClick = (user) => {
    console.log('User clicked:', user);
  };
  
  if (loading) return <div>Loading...</div>;
  
  return <UserList users={users} onUserClick={handleUserClick} />;
}

    Render Props

    // ========== Render Prop Component ==========
function MouseTracker({ render }) {
  const [position, setPosition] = useState({ x: 0, y: 0 });
  
  useEffect(() => {
    const handleMouseMove = (e) => {
      setPosition({ x: e.clientX, y: e.clientY });
    };
    
    window.addEventListener('mousemove', handleMouseMove);
    return () => window.removeEventListener('mousemove', handleMouseMove);
  }, []);
  
  return render(position);
}

// Usage
function App() {
  return (
    <MouseTracker
      render={({ x, y }) => (
        <div>Mouse position: {x}, {y}</div>
      )}
    />
  );
}

    Higher-Order Components (HOC)

    // ========== HOC ==========
function withLoading(Component) {
  return function WithLoadingComponent({ isLoading, ...props }) {
    if (isLoading) {
      return <div>Loading...</div>;
    }
    return <Component {...props} />;
  };
}

// Usage
const UserListWithLoading = withLoading(UserList);

function App() {
  const [isLoading, setIsLoading] = useState(true);
  const [users, setUsers] = useState([]);
  
  return <UserListWithLoading isLoading={isLoading} users={users} />;
}

    Best Practices

  • Keep components small and focused - Single responsibility
  • Use functional components - Prefer hooks over class components
  • Destructure props - Cleaner and more readable
  • Use TypeScript - Type safety and better tooling
  • Avoid inline functions in JSX - Use useCallback
  • Use keys properly - Unique and stable keys for lists
  • Don't mutate state - Always create new objects/arrays
  • Use fragments - Avoid unnecessary DOM nodes
  • Handle errors - Use error boundaries
  • Optimize performance - Use React.memo, useMemo, useCallback

    • TypeScript with React

    // ========== Component Props ==========
interface ButtonProps {
  text: string;
  onClick: () => void;
  disabled?: boolean;
}

function Button({ text, onClick, disabled = false }: ButtonProps) {
  return (
    <button onClick={onClick} disabled={disabled}>
      {text}
    </button>
  );
}

// ========== With Children ==========
interface CardProps {
  title: string;
  children: React.ReactNode;
}

function Card({ title, children }: CardProps) {
  return (
    <div>
      <h2>{title}</h2>
      {children}
    </div>
  );
}

// ========== Event Handlers ==========
function Form() {
  const handleSubmit = (e: React.FormEvent<HTMLFormElement>) => {
    e.preventDefault();
  };
  
  const handleChange = (e: React.ChangeEvent<HTMLInputElement>) => {
    console.log(e.target.value);
  };
  
  return (
    <form onSubmit={handleSubmit}>
      <input onChange={handleChange} />
    </form>
  );
}

// ========== Generic Components ==========
interface ListProps<T> {
  items: T[];
  renderItem: (item: T) => React.ReactNode;
}

function List<T>({ items, renderItem }: ListProps<T>) {
  return (
    <ul>
      {items.map((item, index) => (
        <li key={index}>{renderItem(item)}</li>
      ))}
    </ul>
  );
}

    Resources

  • React Documentation
  • React Beta Docs
  • React TypeScript Cheatsheet
  • Awesome React
  • React Patterns

    • Topics

    ReactJavaScriptTypeScriptHooksComponents
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