React Patterns

by manutej1861cc9720d5No license62 starsListed Oct 8, 2026Updated Oct 8, 2026Repository updated 3 months ago

Modern React development with hooks, component patterns, state management, and performance optimization for building scalable applications

Instructions onlySoftware Development
AI-generated overview

Reference guide for modern React patterns, covering hooks, component composition, state management and performance optimization.

What it does
This skill is an instructional reference on modern React development. It explains built-in hooks such as useState, useReducer, useContext, useEffect, useMemo, useCallback, useRef and React 18 transition and server-action hooks, with syntax, code examples and guidance on when to use each. It also covers component types, custom hook patterns, memoization and common pitfalls like missing effect dependencies.
When to use it
Use it when building or refactoring React applications with functional components and hooks, choosing state management approaches, extracting reusable custom hooks, or diagnosing unnecessary re-renders and performance issues. It also suits work involving Server Components and server actions.
Requirements
No scripts or tooling are required; it is an instructions-only reference. Examples assume a React 18+ project and, for server action examples, a server environment with a database, but nothing needs to be installed to read the guidance.

React Patterns - Modern Development Guide

A comprehensive skill for mastering modern React development patterns, including React 18+ features, hooks, component composition, state management strategies, and performance optimization techniques for building scalable web applications.

When to Use This Skill

Use this skill when:

  • Building modern React applications with functional components and hooks
  • Implementing complex state management with useReducer and Context API
  • Optimizing React application performance with memoization techniques
  • Creating reusable custom hooks for shared logic
  • Working with Server Components and React Server Components (RSC)
  • Managing forms, side effects, and asynchronous operations
  • Refactoring class components to modern functional patterns
  • Building type-safe React applications with proper patterns
  • Implementing advanced component composition patterns
  • Debugging React performance issues and unnecessary re-renders

Core Concepts

React Philosophy

Modern React emphasizes:

  • Functional Components: Pure functions that return JSX
  • Hooks: Composable state and side effect management
  • Declarative UI: Describe what the UI should look like, React handles updates
  • Component Composition: Build complex UIs from simple, reusable components
  • Unidirectional Data Flow: Props flow down, events flow up
  • Immutability: Never mutate state directly, always create new objects/arrays

Component Types

  1. Presentational Components: Focus on UI, receive data via props
  2. Container Components: Handle logic, state, and side effects
  3. Server Components: Render on the server, no client JavaScript
  4. Client Components: Interactive components marked with "use client"
  5. Async Components: Server components that can await data

React Hooks Reference

Built-in State Hooks

useState

Manage local component state for simple values.

Syntax:

javascript
const [state, setState] = useState(initialValue);

Basic Example:

javascript
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(prev => prev + 1)}>Increment (functional)</button>    </div>  );}

Best Practices:

  • Use functional updates when new state depends on previous state
  • Keep state as local as possible
  • Don't store derived values in state
  • Initialize with functions for expensive computations

Multiple State Variables:

javascript
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 type="number" value={age} onChange={e => setAge(Number(e.target.value))} />    </form>  );}

Lazy Initialization:

javascript
function ExpensiveComponent() {  // Function only runs once on initial render  const [state, setState] = useState(() => {    const initialValue = expensiveComputation();    return initialValue;  });
  return <div>{state}</div>;}
useReducer

Manage complex state logic with a reducer pattern (similar to Redux).

Syntax:

javascript
const [state, dispatch] = useReducer(reducer, initialState, init?);

Task Manager Example:

javascript
import { useReducer } from 'react';
function tasksReducer(tasks, action) {  switch (action.type) {    case 'added':      return [...tasks, {        id: action.id,        text: action.text,        done: false      }];    case 'changed':      return tasks.map(t =>        t.id === action.task.id ? action.task : t      );    case 'deleted':      return tasks.filter(t => t.id !== action.id);    default:      throw Error('Unknown action: ' + action.type);  }}
function TaskApp() {  const [tasks, dispatch] = useReducer(tasksReducer, []);
  function handleAddTask(text) {    dispatch({      type: 'added',      id: Date.now(),      text: text,    });  }
  function handleChangeTask(task) {    dispatch({      type: 'changed',      task: task    });  }
  function handleDeleteTask(taskId) {    dispatch({      type: 'deleted',      id: taskId    });  }
  return (    <>      <AddTask onAddTask={handleAddTask} />      <TaskList        tasks={tasks}        onChangeTask={handleChangeTask}        onDeleteTask={handleDeleteTask}      />    </>  );}

When to use useReducer:

  • Multiple related state values
  • Complex state update logic
  • State transitions follow predictable patterns
  • Need to optimize performance with many updates
  • Want to separate state logic from component
useContext

Access context values without prop drilling.

Syntax:

javascript
const value = useContext(SomeContext);

Theme Context Example:

javascript
import { createContext, useContext, useState } from 'react';
const ThemeContext = createContext(null);
export function ThemeProvider({ children }) {  const [theme, setTheme] = useState('light');
  const toggleTheme = () => {    setTheme(prev => prev === 'light' ? 'dark' : 'light');  };
  return (    <ThemeContext.Provider value={{ theme, toggleTheme }}>      {children}    </ThemeContext.Provider>  );}
export function useTheme() {  const context = useContext(ThemeContext);  if (!context) {    throw new Error('useTheme must be used within ThemeProvider');  }  return context;}
// Usagefunction Button() {  const { theme, toggleTheme } = useTheme();
  return (    <button      onClick={toggleTheme}      className={theme === 'dark' ? 'btn-dark' : 'btn-light'}    >      Toggle Theme    </button>  );}

Combining useReducer + useContext:

javascript
import { createContext, useContext, useReducer } from 'react';
const TasksContext = createContext(null);const TasksDispatchContext = createContext(null);
export function TasksProvider({ children }) {  const [tasks, dispatch] = useReducer(tasksReducer, initialTasks);
  return (    <TasksContext.Provider value={tasks}>      <TasksDispatchContext.Provider value={dispatch}>        {children}      </TasksDispatchContext.Provider>    </TasksContext.Provider>  );}
export function useTasks() {  return useContext(TasksContext);}
export function useTasksDispatch() {  return useContext(TasksDispatchContext);}
// Usage in componentsfunction TaskList() {  const tasks = useTasks();  const dispatch = useTasksDispatch();
  return (    <ul>      {tasks.map(task => (        <li key={task.id}>          {task.text}          <button onClick={() => dispatch({ type: 'deleted', id: task.id })}>            Delete          </button>        </li>      ))}    </ul>  );}

Effect Hooks

useEffect

Synchronize component with external systems (APIs, DOM, subscriptions).

Syntax:

javascript
useEffect(() => {  // Effect logic  return () => {    // Cleanup logic  };}, [dependencies]);

Data Fetching Example:

javascript
import { useState, useEffect } from 'react';
function UserProfile({ userId }) {  const [user, setUser] = useState(null);  const [loading, setLoading] = useState(true);  const [error, setError] = useState(null);
  useEffect(() => {    let ignore = false; // Prevent race conditions
    async function fetchUser() {      try {        setLoading(true);        const response = await fetch(`/api/users/${userId}`);        const data = await response.json();
        if (!ignore) {          setUser(data);        }      } catch (err) {        if (!ignore) {          setError(err.message);        }      } finally {        if (!ignore) {          setLoading(false);        }      }    }
    fetchUser();
    return () => {      ignore = true; // Cleanup    };  }, [userId]);
  if (loading) return <div>Loading...</div>;  if (error) return <div>Error: {error}</div>;  return <div>User: {user?.name}</div>;}

Subscription Example:

javascript
function ChatRoom({ roomId }) {  const [messages, setMessages] = useState([]);
  useEffect(() => {    const connection = createConnection(roomId);
    connection.on('message', (msg) => {      setMessages(prev => [...prev, msg]);    });
    connection.connect();
    return () => {      connection.disconnect(); // Cleanup on unmount or roomId change    };  }, [roomId]);
  return (    <div>      {messages.map((msg, i) => (        <div key={i}>{msg}</div>      ))}    </div>  );}

Common Effect Patterns:

javascript
// Run once on mountuseEffect(() => {  console.log('Component mounted');}, []); // Empty dependency array
// Run on every renderuseEffect(() => {  console.log('Component rendered');}); // No dependency array
// Run when specific values changeuseEffect(() => {  console.log('userId changed:', userId);}, [userId]); // Dependency array with values
// Cleanup on unmountuseEffect(() => {  const timer = setTimeout(() => {    console.log('Delayed action');  }, 1000);
  return () => clearTimeout(timer);}, []);
useLayoutEffect

Synchronous version of useEffect, runs before browser paint.

Use Cases:

  • Measuring DOM elements
  • Synchronous DOM mutations
  • Preventing visual flickering

Example:

javascript
import { useLayoutEffect, useRef, useState } from 'react';
function Tooltip() {  const ref = useRef(null);  const [tooltipHeight, setTooltipHeight] = useState(0);
  useLayoutEffect(() => {    const { height } = ref.current.getBoundingClientRect();    setTooltipHeight(height); // Synchronous update before paint  }, []);
  return (    <div ref={ref}>      Tooltip content (height: {tooltipHeight}px)    </div>  );}

Performance Hooks

useMemo

Cache expensive computations between renders.

Syntax:

javascript
const cachedValue = useMemo(() => computeExpensiveValue(a, b), [a, b]);

Example:

javascript
import { useMemo } from 'react';
function TodoList({ todos, filter }) {  // Only recompute when todos or filter changes  const visibleTodos = useMemo(() => {    console.log('Filtering todos...');    return todos.filter(todo => {      if (filter === 'all') return true;      if (filter === 'active') return !todo.done;      if (filter === 'completed') return todo.done;      return true;    });  }, [todos, filter]);
  return (    <ul>      {visibleTodos.map(todo => (        <li key={todo.id}>{todo.text}</li>      ))}    </ul>  );}

When to use useMemo:

  • Expensive calculations (filtering, sorting large arrays)
  • Preventing unnecessary re-renders of child components
  • Stabilizing object/array references passed as dependencies

Anti-pattern (unnecessary):

javascript
// ❌ Don't use for simple calculationsconst sum = useMemo(() => a + b, [a, b]); // Overkill
// ✅ Just compute directlyconst sum = a + b;
useCallback

Memoize function references between renders.

Syntax:

javascript
const cachedFn = useCallback(() => {  // Function logic}, [dependencies]);

Example:

javascript
import { useState, useCallback, memo } from 'react';
const TodoItem = memo(function TodoItem({ todo, onChange, onDelete }) {  console.log('TodoItem rendered:', todo.id);
  return (    <li>      <input        type="checkbox"        checked={todo.done}        onChange={() => onChange(todo)}      />      {todo.text}      <button onClick={() => onDelete(todo.id)}>Delete</button>    </li>  );});
function TodoList() {  const [todos, setTodos] = useState([]);
  // Memoize handlers to prevent TodoItem re-renders  const handleChange = useCallback((todo) => {    setTodos(prev => prev.map(t =>      t.id === todo.id ? { ...t, done: !t.done } : t    ));  }, []);
  const handleDelete = useCallback((id) => {    setTodos(prev => prev.filter(t => t.id !== id));  }, []);
  return (    <ul>      {todos.map(todo => (        <TodoItem          key={todo.id}          todo={todo}          onChange={handleChange}          onDelete={handleDelete}        />      ))}    </ul>  );}

When to use useCallback:

  • Passing callbacks to memoized child components
  • Function is a dependency of useEffect or other hooks
  • Optimizing expensive event handlers
React.memo

Memoize entire component to prevent unnecessary re-renders.

Syntax:

javascript
const MemoizedComponent = memo(function Component(props) {  // Component logic}, arePropsEqual?);

Example:

javascript
import { memo } from 'react';
const ExpensiveComponent = memo(function ExpensiveComponent({ data, onClick }) {  console.log('ExpensiveComponent rendered');
  return (    <div>      {data.map(item => (        <div key={item.id} onClick={() => onClick(item)}>          {item.name}        </div>      ))}    </div>  );});
// With custom comparisonconst CustomMemoComponent = memo(  function CustomMemoComponent({ user }) {    return <div>{user.name}</div>;  },  (prevProps, nextProps) => {    // Return true if props are equal (skip re-render)    return prevProps.user.id === nextProps.user.id;  });

Ref Hooks

useRef

Create mutable reference that persists across renders.

Syntax:

javascript
const ref = useRef(initialValue);

DOM Reference Example:

javascript
import { useRef } from 'react';
function VideoPlayer({ src, isPlaying }) {  const videoRef = useRef(null);
  useEffect(() => {    if (isPlaying) {      videoRef.current.play();    } else {      videoRef.current.pause();    }  }, [isPlaying]);
  return <video ref={videoRef} src={src} />;}

Storing Mutable Values:

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

Previous Value Pattern:

javascript
function usePrevious(value) {  const ref = useRef();
  useEffect(() => {    ref.current = value;  }, [value]);
  return ref.current;}
// Usagefunction Counter({ count }) {  const prevCount = usePrevious(count);
  return (    <div>      <p>Current: {count}</p>      <p>Previous: {prevCount}</p>    </div>  );}

Transition Hooks (React 18+)

useTransition

Mark state updates as non-urgent, keeping UI responsive.

Syntax:

javascript
const [isPending, startTransition] = useTransition();

Example:

javascript
import { useState, useTransition } from 'react';
function SearchResults() {  const [query, setQuery] = useState('');  const [results, setResults] = useState([]);  const [isPending, startTransition] = useTransition();
  function handleChange(e) {    const value = e.target.value;    setQuery(value); // Urgent update (input value)
    startTransition(() => {      // Non-urgent update (search results)      const filtered = performExpensiveSearch(value);      setResults(filtered);    });  }
  return (    <div>      <input value={query} onChange={handleChange} />      {isPending && <div>Searching...</div>}      <ul>        {results.map(result => (          <li key={result.id}>{result.name}</li>        ))}      </ul>    </div>  );}
useDeferredValue

Defer updating part of the UI.

Syntax:

javascript
const deferredValue = useDeferredValue(value);

Example:

javascript
import { useState, useDeferredValue, memo } from 'react';
const SlowList = memo(function SlowList({ items }) {  // Intentionally slow rendering  return (    <ul>      {items.map(item => (        <li key={item.id}>{item.name}</li>      ))}    </ul>  );});
function App() {  const [text, setText] = useState('');  const deferredText = useDeferredValue(text);
  return (    <>      <input value={text} onChange={e => setText(e.target.value)} />      <SlowList items={filterItems(deferredText)} />    </>  );}

Server Action Hooks (RSC)

useActionState

Manage server action state and pending status.

Syntax:

javascript
const [state, formAction, isPending] = useActionState(serverAction, initialState);

Example:

javascript
"use client";
import { useActionState } from 'react';import { updateName } from './actions';
function UpdateNameForm() {  const [state, submitAction, isPending] = useActionState(    updateName,    { error: null }  );
  return (    <form action={submitAction}>      <input type="text" name="name" disabled={isPending} />      {state.error && <span className="error">{state.error}</span>}      <button type="submit" disabled={isPending}>        {isPending ? 'Updating...' : 'Update'}      </button>    </form>  );}

Server Action (actions.js):

javascript
"use server";
export async function updateName(prevState, formData) {  const name = formData.get('name');
  if (!name) {    return { error: 'Name is required' };  }
  try {    await db.users.updateName(name);    return { error: null };  } catch (err) {    return { error: 'Failed to update name' };  }}

Custom Hooks Patterns

Custom hooks let you extract and reuse stateful logic across components.

Naming Convention

Always prefix custom hooks with use:

javascript
useCustomHook // ✅ CorrectcustomHook    // ❌ Wrong

Data Fetching Hook

javascript
import { useState, useEffect } from 'react';
export function useFetch(url) {  const [data, setData] = useState(null);  const [loading, setLoading] = useState(true);  const [error, setError] = useState(null);
  useEffect(() => {    let ignore = false;
    async function fetchData() {      try {        setLoading(true);        setError(null);
        const response = await fetch(url);        if (!response.ok) {          throw new Error(`HTTP error! status: ${response.status}`);        }
        const result = await response.json();
        if (!ignore) {          setData(result);        }      } catch (err) {        if (!ignore) {          setError(err.message);        }      } finally {        if (!ignore) {          setLoading(false);        }      }    }
    fetchData();
    return () => {      ignore = true;    };  }, [url]);
  return { data, loading, error };}
// Usagefunction UserProfile({ userId }) {  const { data: user, loading, error } = useFetch(`/api/users/${userId}`);
  if (loading) return <div>Loading...</div>;  if (error) return <div>Error: {error}</div>;  return <div>{user.name}</div>;}

Form Input Hook

javascript
import { useState } from 'react';
export function useFormInput(initialValue = '') {  const [value, setValue] = useState(initialValue);
  function handleChange(e) {    setValue(e.target.value);  }
  function reset() {    setValue(initialValue);  }
  return {    value,    onChange: handleChange,    reset  };}
// Usagefunction LoginForm() {  const email = useFormInput('');  const password = useFormInput('');
  function handleSubmit(e) {    e.preventDefault();    console.log('Email:', email.value);    console.log('Password:', password.value);    email.reset();    password.reset();  }
  return (    <form onSubmit={handleSubmit}>      <input type="email" {...email} placeholder="Email" />      <input type="password" {...password} placeholder="Password" />      <button type="submit">Login</button>    </form>  );}

Local Storage Hook

javascript
import { useState, useEffect } from 'react';
export function useLocalStorage(key, initialValue) {  const [value, setValue] = useState(() => {    try {      const item = window.localStorage.getItem(key);      return item ? JSON.parse(item) : initialValue;    } catch (error) {      console.error(error);      return initialValue;    }  });
  useEffect(() => {    try {      window.localStorage.setItem(key, JSON.stringify(value));    } catch (error) {      console.error(error);    }  }, [key, value]);
  return [value, setValue];}
// Usagefunction Settings() {  const [theme, setTheme] = useLocalStorage('theme', 'light');  const [language, setLanguage] = useLocalStorage('language', 'en');
  return (    <div>      <select value={theme} onChange={e => setTheme(e.target.value)}>        <option value="light">Light</option>        <option value="dark">Dark</option>      </select>      <select value={language} onChange={e => setLanguage(e.target.value)}>        <option value="en">English</option>        <option value="es">Spanish</option>      </select>    </div>  );}

Debounce Hook

javascript
import { useState, useEffect } from 'react';
export function useDebounce(value, delay = 500) {  const [debouncedValue, setDebouncedValue] = useState(value);
  useEffect(() => {    const handler = setTimeout(() => {      setDebouncedValue(value);    }, delay);
    return () => {      clearTimeout(handler);    };  }, [value, delay]);
  return debouncedValue;}
// Usagefunction SearchComponent() {  const [searchTerm, setSearchTerm] = useState('');  const debouncedSearchTerm = useDebounce(searchTerm, 500);
  useEffect(() => {    if (debouncedSearchTerm) {      // Perform search      console.log('Searching for:', debouncedSearchTerm);    }  }, [debouncedSearchTerm]);
  return (    <input      type="text"      value={searchTerm}      onChange={e => setSearchTerm(e.target.value)}      placeholder="Search..."    />  );}

Window Size Hook

javascript
import { useState, useEffect } from 'react';
export function useWindowSize() {  const [windowSize, setWindowSize] = useState({    width: undefined,    height: undefined,  });
  useEffect(() => {    function handleResize() {      setWindowSize({        width: window.innerWidth,        height: window.innerHeight,      });    }
    handleResize(); // Set initial size    window.addEventListener('resize', handleResize);
    return () => window.removeEventListener('resize', handleResize);  }, []);
  return windowSize;}
// Usagefunction ResponsiveComponent() {  const { width, height } = useWindowSize();
  return (    <div>      <p>Window width: {width}px</p>      <p>Window height: {height}px</p>      {width < 768 ? <MobileView /> : <DesktopView />}    </div>  );}

Online Status Hook

javascript
import { useState, useEffect } from 'react';
export function useOnlineStatus() {  const [isOnline, setIsOnline] = useState(navigator.onLine);
  useEffect(() => {    function handleOnline() {      setIsOnline(true);    }
    function handleOffline() {      setIsOnline(false);    }
    window.addEventListener('online', handleOnline);    window.addEventListener('offline', handleOffline);
    return () => {      window.removeEventListener('online', handleOnline);      window.removeEventListener('offline', handleOffline);    };  }, []);
  return isOnline;}
// Usagefunction StatusBar() {  const isOnline = useOnlineStatus();
  return (    <div className={isOnline ? 'online' : 'offline'}>      {isOnline ? '✅ Online' : '❌ Offline'}    </div>  );}

Component Patterns

Compound Components

Build components that work together while sharing implicit state.

javascript
import { createContext, useContext, useState } from 'react';
const TabsContext = createContext();
export function Tabs({ children, defaultValue }) {  const [activeTab, setActiveTab] = useState(defaultValue);
  return (    <TabsContext.Provider value={{ activeTab, setActiveTab }}>      <div className="tabs">{children}</div>    </TabsContext.Provider>  );}
export function TabList({ children }) {  return <div className="tab-list">{children}</div>;}
export function Tab({ value, children }) {  const { activeTab, setActiveTab } = useContext(TabsContext);  const isActive = activeTab === value;
  return (    <button      className={`tab ${isActive ? 'active' : ''}`}      onClick={() => setActiveTab(value)}    >      {children}    </button>  );}
export function TabPanels({ children }) {  return <div className="tab-panels">{children}</div>;}
export function TabPanel({ value, children }) {  const { activeTab } = useContext(TabsContext);
  if (activeTab !== value) return null;
  return <div className="tab-panel">{children}</div>;}
// Usagefunction App() {  return (    <Tabs defaultValue="tab1">      <TabList>        <Tab value="tab1">Tab 1</Tab>        <Tab value="tab2">Tab 2</Tab>        <Tab value="tab3">Tab 3</Tab>      </TabList>
      <TabPanels>        <TabPanel value="tab1">Content for Tab 1</TabPanel>        <TabPanel value="tab2">Content for Tab 2</TabPanel>        <TabPanel value="tab3">Content for Tab 3</TabPanel>      </TabPanels>    </Tabs>  );}

Render Props

Share code between components using a prop whose value is a function.

javascript
function DataFetcher({ url, render }) {  const [data, setData] = useState(null);  const [loading, setLoading] = useState(true);
  useEffect(() => {    fetch(url)      .then(res => res.json())      .then(data => {        setData(data);        setLoading(false);      });  }, [url]);
  return render({ data, loading });}
// Usagefunction App() {  return (    <DataFetcher      url="/api/users"      render={({ data, loading }) => (        loading ? <div>Loading...</div> : (          <ul>            {data?.map(user => (              <li key={user.id}>{user.name}</li>            ))}          </ul>        )      )}    />  );}

Higher-Order Components (HOC)

Wrap components to enhance functionality.

javascript
import { useEffect, useState } from 'react';
// HOC for data fetchingfunction withData(Component, url) {  return function WithDataComponent(props) {    const [data, setData] = useState(null);    const [loading, setLoading] = useState(true);
    useEffect(() => {      fetch(url)        .then(res => res.json())        .then(data => {          setData(data);          setLoading(false);        });    }, []);
    return <Component {...props} data={data} loading={loading} />;  };}
// Original componentfunction UserList({ data, loading }) {  if (loading) return <div>Loading...</div>;
  return (    <ul>      {data?.map(user => (        <li key={user.id}>{user.name}</li>      ))}    </ul>  );}
// Enhanced componentconst UserListWithData = withData(UserList, '/api/users');
// Usagefunction App() {  return <UserListWithData />;}

Container/Presenter Pattern

Separate logic from presentation.

javascript
// Container (logic)function UserListContainer() {  const [users, setUsers] = useState([]);  const [loading, setLoading] = useState(true);  const [searchTerm, setSearchTerm] = useState('');
  useEffect(() => {    fetchUsers().then(data => {      setUsers(data);      setLoading(false);    });  }, []);
  const filteredUsers = users.filter(user =>    user.name.toLowerCase().includes(searchTerm.toLowerCase())  );
  return (    <UserListPresenter      users={filteredUsers}      loading={loading}      searchTerm={searchTerm}      onSearchChange={setSearchTerm}    />  );}
// Presenter (UI)function UserListPresenter({ users, loading, searchTerm, onSearchChange }) {  if (loading) return <div>Loading...</div>;
  return (    <div>      <input        type="text"        value={searchTerm}        onChange={e => onSearchChange(e.target.value)}        placeholder="Search users..."      />      <ul>        {users.map(user => (          <li key={user.id}>{user.name}</li>        ))}      </ul>    </div>  );}

Performance Optimization

Identifying Performance Issues

Use React DevTools Profiler to identify:

  • Components re-rendering unnecessarily
  • Expensive render operations
  • State update cascades

Optimization Strategies

1. Memoization
javascript
import { memo, useMemo, useCallback } from 'react';
const ExpensiveList = memo(function ExpensiveList({ items, onItemClick }) {  console.log('Rendering ExpensiveList');
  return (    <ul>      {items.map(item => (        <li key={item.id} onClick={() => onItemClick(item.id)}>          {item.name}        </li>      ))}    </ul>  );});
function App() {  const [items, setItems] = useState([]);  const [count, setCount] = useState(0);
  // Memoize expensive computation  const sortedItems = useMemo(() => {    console.log('Sorting items...');    return [...items].sort((a, b) => a.name.localeCompare(b.name));  }, [items]);
  // Memoize callback  const handleItemClick = useCallback((id) => {    console.log('Item clicked:', id);  }, []);
  return (    <div>      <button onClick={() => setCount(c => c + 1)}>Count: {count}</button>      <ExpensiveList items={sortedItems} onItemClick={handleItemClick} />    </div>  );}
2. Code Splitting
javascript
import { lazy, Suspense } from 'react';
// Lazy load componentsconst HeavyComponent = lazy(() => import('./HeavyComponent'));const Dashboard = lazy(() => import('./Dashboard'));
function App() {  return (    <Suspense fallback={<div>Loading...</div>}>      <HeavyComponent />    </Suspense>  );}
// Route-based splittingimport { BrowserRouter, Routes, Route } from 'react-router-dom';
function App() {  return (    <BrowserRouter>      <Suspense fallback={<div>Loading...</div>}>        <Routes>          <Route path="/" element={<Home />} />          <Route path="/dashboard" element={<Dashboard />} />        </Routes>      </Suspense>    </BrowserRouter>  );}
3. Virtualization
javascript
import { FixedSizeList } from 'react-window';
function VirtualizedList({ items }) {  const Row = ({ index, style }) => (    <div style={style}>      {items[index].name}    </div>  );
  return (    <FixedSizeList      height={500}      itemCount={items.length}      itemSize={50}      width="100%"    >      {Row}    </FixedSizeList>  );}
4. Avoid Anonymous Functions
javascript
// ❌ Bad - creates new function on every renderfunction List({ items }) {  return (    <ul>      {items.map(item => (        <li key={item.id} onClick={() => console.log(item.id)}>          {item.name}        </li>      ))}    </ul>  );}
// ✅ Good - use useCallbackfunction List({ items }) {  const handleClick = useCallback((id) => {    console.log(id);  }, []);
  return (    <ul>      {items.map(item => (        <li key={item.id} onClick={() => handleClick(item.id)}>          {item.name}        </li>      ))}    </ul>  );}

Server Components (RSC)

React Server Components render on the server, reducing client bundle size.

Server Component

javascript
// app/users/page.js (Server Component by default)async function UsersPage() {  // Fetch data directly on server  const users = await db.users.findAll();
  return (    <div>      <h1>Users</h1>      <ul>        {users.map(user => (          <li key={user.id}>{user.name}</li>        ))}      </ul>    </div>  );}
export default UsersPage;

Client Component

javascript
// components/Counter.js"use client"; // Mark as client component
import { useState } from 'react';
export default function Counter() {  const [count, setCount] = useState(0);
  return (    <button onClick={() => setCount(c => c + 1)}>      Count: {count}    </button>  );}

Composition Pattern

javascript
// app/page.js (Server Component)import Counter from '@/components/Counter'; // Client Component
async function HomePage() {  const data = await fetchData(); // Server-side data fetching
  return (    <div>      <h1>{data.title}</h1>      <p>{data.description}</p>      <Counter /> {/* Interactive client component */}    </div>  );}
export default HomePage;

State Management Strategies

Local State (useState)

Best for: Component-specific state

javascript
function Counter() {  const [count, setCount] = useState(0);  return <button onClick={() => setCount(c => c + 1)}>{count}</button>;}

Lifted State

Best for: Shared state between sibling components

javascript
function Parent() {  const [sharedValue, setSharedValue] = useState('');
  return (    <>      <ChildA value={sharedValue} onChange={setSharedValue} />      <ChildB value={sharedValue} />    </>  );}

Context API

Best for: App-wide state (theme, auth, language)

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

useReducer + Context

Best for: Complex state logic with multiple actions

javascript
const StateContext = createContext();const DispatchContext = createContext();
function reducer(state, action) {  switch (action.type) {    case 'ADD_ITEM':      return { ...state, items: [...state.items, action.payload] };    case 'REMOVE_ITEM':      return { ...state, items: state.items.filter(i => i.id !== action.payload) };    default:      return state;  }}
function StoreProvider({ children }) {  const [state, dispatch] = useReducer(reducer, { items: [] });
  return (    <StateContext.Provider value={state}>      <DispatchContext.Provider value={dispatch}>        {children}      </DispatchContext.Provider>    </StateContext.Provider>  );}

Best Practices

1. Component Design

  • Keep components small and focused (Single Responsibility)
  • Extract reusable logic into custom hooks
  • Prefer composition over inheritance
  • Use prop spreading sparingly
  • Define PropTypes or TypeScript types

2. State Management

  • Keep state as local as possible
  • Lift state only when necessary
  • Avoid unnecessary state (derive from props when possible)
  • Use reducers for complex state logic
  • Batch state updates when possible

3. Performance

  • Don't optimize prematurely - measure first
  • Use React DevTools Profiler
  • Memoize expensive computations
  • Avoid creating objects/arrays in render
  • Use key prop correctly for lists

4. Effects

  • Keep effects focused (one concern per effect)
  • Always specify dependencies
  • Clean up effects (return cleanup function)
  • Use AbortController for fetch requests
  • Avoid race conditions with ignore flags

5. Code Organization

src/├── components/│   ├── common/         # Reusable UI components│   ├── features/       # Feature-specific components│   └── layout/         # Layout components├── hooks/              # Custom hooks├── context/            # Context providers├── utils/              # Utility functions├── services/           # API services└── types/              # TypeScript types

Common Anti-Patterns to Avoid

1. Mutating State

javascript
// ❌ Wrongconst handleAdd = () => {  items.push(newItem);  setItems(items);};
// ✅ Correctconst handleAdd = () => {  setItems([...items, newItem]);};

2. Missing Dependencies

javascript
// ❌ WronguseEffect(() => {  console.log(userId);}, []); // Missing userId dependency
// ✅ CorrectuseEffect(() => {  console.log(userId);}, [userId]);

3. Conditional Hooks

javascript
// ❌ Wrongif (condition) {  const [state, setState] = useState(0);}
// ✅ Correctconst [state, setState] = useState(0);if (condition) {  // Use state}

4. Creating Components Inside Components

javascript
// ❌ Wrongfunction Parent() {  function Child() { // Re-created on every render    return <div>Child</div>;  }  return <Child />;}
// ✅ Correctfunction Child() {  return <div>Child</div>;}
function Parent() {  return <Child />;}

Troubleshooting

Common Issues

Issue: Infinite re-render loop

  • Check useEffect dependencies
  • Avoid setting state directly in render
  • Use functional updates: setState(prev => prev + 1)

Issue: Stale closure

  • Use functional updates in setState
  • Add missing dependencies to useEffect
  • Use useRef for mutable values

Issue: Component not re-rendering

  • Check if state is being mutated (use immutable updates)
  • Verify React.memo comparison function
  • Ensure new reference for objects/arrays

Issue: Memory leak warning

  • Clean up effects (return cleanup function)
  • Cancel ongoing requests on unmount
  • Clear timers/intervals

Resources

Skill Version: 1.0.0 Last Updated: October 2025 Skill Category: Frontend Development, React, JavaScript Compatible With: React 18+, Next.js 13+, TypeScript

Source and attribution

Source:manutej/luxor-claude-marketplaceinplugins/luxor-frontend-essentials/skills/react-patternsat commit1861cc9

License: No license

Content belongs to its original authors. SourceWeft indexes it from a public repository.

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