React

React Best Practices Skill

Overview

This skill provides React best practices for building modern web applications using React and Next.js. It follows official React documentation and 2025 community standards, emphasizing feature-based architecture, TypeScript integration, state management patterns, performance optimization, and testing guidelines.

Quick Start: Creating Components

When creating React components, follow these core principles from Official React Rules:

1. Component Structure

// ✅ Good: Functional component with TypeScript
interface ButtonProps {
  label: string;
  onClick: () => void;
  variant?: 'primary' | 'secondary';
}

export function Button({ label, onClick, variant = 'primary' }: ButtonProps) {
  return (
    <button className={`btn btn-${variant}`}
      {label}
    </button>
  );
}

Key Rules:

• Components must be pure - same inputs = same output
• Never call components directly (<MyComponent /> not MyComponent())
• Always call Hooks at the top level of the component
• Only call Hooks from React functions (not regular JavaScript functions)

2. Component Organization

// ✅ Good: Co-locate related code
// src/features/auth/components/LoginForm.tsx

import { useState } from 'react';
import type { LoginCredentials } from '../types';

export function LoginForm() {
  const [credentials, setCredentials] = useState<LoginCredentials>({
    username: '',
    password: '',
  });

  // Component logic here
}

Project Structure

Use feature-based architecture for scalable React applications:

src/
├── app/                    # Next.js app router (if using Next.js)
├── features/               # Feature modules
│   ├── auth/              # Authentication feature
│   │   ├── components/    # Feature-specific components
│   │   │   ├── LoginForm.tsx
│   │   │   └── RegisterForm.tsx
│   │   ├── hooks/         # Feature-specific hooks
│   │   │   └── useAuth.ts
│   │   ├── api/           # API calls
│   │   │   └── authApi.ts
│   │   ├── types/         # TypeScript types
│   │   │   └── auth.types.ts
│   │   └── index.ts       # Public exports
│   └── dashboard/         # Dashboard feature
├── shared/                # Shared utilities
│   ├── components/        # Common UI components
│   │   ├── Button/
│   │   │   ├── Button.tsx
│   │   │   ├── Button.test.tsx
│   │   │   └── index.ts
│   │   └── Input/
│   ├── hooks/             # Shared custom hooks
│   │   └── useLocalStorage.ts
│   ├── utils/             # Helper functions
│   │   └── format.ts
│   └── types/             # Shared types
│       └── api.types.ts
└── lib/                   # External library configs
    ├── react-query/
    └── tests/

Principles:

• Group by feature, not by file type
• Co-locate related code (component, hooks, types, tests)
• Keep shared utilities separate
• Use index.ts for clean imports

For detailed structure guidance, see references/project-structure.md

Core React Best Practices

1. State Management

Choose the right state management approach based on your needs:

useState - Simple, independent state

const [count, setCount] = useState(0);

useReducer - Complex state logic with multiple sub-values

const [state, dispatch] = useReducer(formReducer, initialState);

Context API - Shared global state (theme, auth, language)

const AuthContext = createContext<AuthContextValue | null>(null);

Server State - Server data with React Query or SWR

const { data, isLoading } = useQuery({ queryKey: ['users'], queryFn: fetchUsers });

For detailed state management patterns, see references/state-management.md

2. Component Patterns

Composition over Inheritance

// ✅ Good: Composition
<Card>
  <CardHeader title="Welcome" />
  <CardBody>Content here</CardBody>
  <CardFooter>Actions</CardFooter>
</Card>

Custom Hooks for Reusable Logic

// ✅ Good: Extract logic into custom hook
function useForm<T>(initialValues: T) {
  const [values, setValues] = useState(initialValues);
  // ... hook logic
  return { values, handleChange, reset };
}

Props vs State

• Props: Immutable data passed from parent
• State: Mutable data managed within component

3. TypeScript Integration

Component Props

interface UserCardProps {
  user: User;
  onEdit?: (user: User) => void;
  variant?: 'default' | 'compact';
}

export function UserCard({ user, onEdit, variant = 'default' }: UserCardProps) {
  // ...
}

Type Exports

export type { UserCardProps }; // Export alongside component

For comprehensive TypeScript patterns, see references/typescript.md

Performance Optimization

Memoization

// Use useMemo for expensive calculations
const filteredItems = useMemo(
  () => items.filter(item => item.active),
  [items]
);

// Use useCallback for functions passed to children
const handleClick = useCallback((id: string) => {
  // handler logic
}, [dependency]);

Code Splitting

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

For detailed optimization techniques, see references/performance.md

Testing Patterns

Component Testing with React Testing Library

import { render, screen } from '@testing-library/react';
import { Button } from './Button';

test('renders button with label', () => {
  render(<Button label="Click me" />);
  expect(screen.getByText('Click me')).toBeInTheDocument();
});

For comprehensive testing guidelines, see references/testing.md

When to Use Reference Materials

references/project-structure.md

Read when:

• Setting up a new React project
• Restructuring an existing codebase
• Deciding where to place new features
• Organizing large-scale applications

references/state-management.md

Read when:

• Designing state architecture
• Choosing between useState, useReducer, or Context
• Implementing form state
• Managing server state with React Query/SWR

references/performance.md

Read when:

• Optimizing render performance
• Implementing code splitting
• Reducing bundle size
• Working with large lists or data

references/testing.md

Read when:

• Writing component tests
• Testing custom hooks
• Setting up test infrastructure
• Testing async operations

references/typescript.md

Read when:

• Typing component props
• Creating generic components
• Organizing type definitions
• Ensuring type safety throughout the app

Resources

references/

Detailed documentation on specific aspects of React development:

• project-structure.md - Feature-based folder organization and scaling
• state-management.md - State patterns and when to use each approach
• performance.md - Optimization techniques and best practices
• testing.md - Testing patterns with React Testing Library
• typescript.md - TypeScript integration and type organization

assets/

Template files and boilerplate:

• FunctionalComponent.template.tsx - Starting template for components
• FeatureModule.template - Feature module structure template

Common Anti-Patterns to Avoid

❌ Don't:

// Calling components directly
const element = MyComponent();

// Mutating props or state directly
props.user.name = 'John';
state.items.push(newItem);

// Using hooks in conditions or loops
if (condition) {
  useEffect(() => {}, []); // ❌ Wrong
}

// Not providing dependency arrays
useEffect(() => {
  // Missing dependencies
}, []); // ❌ Wrong if dependencies exist

✅ Do:

// Using JSX
const element = <MyComponent />;

// Creating new copies
setUser({ ...user, name: 'John' });
setItems([...items, newItem]);

// Hooks at top level
useEffect(() => {}, []); // ✅ Correct

// Complete dependency arrays
useEffect(() => {
  // All dependencies included
}, [dep1, dep2]); // ✅ Correct

Key Takeaways

1. Follow the Rules of React - Keep components pure, call Hooks correctly
2. Use feature-based architecture - Group code by feature, not type
3. TypeScript is essential - Use proper types for all components and props
4. Optimize intentionally - Measure first, then optimize with memoization
5. Test user behavior - Test what users see and interact with
6. Co-locate related code - Keep components with their hooks, types, and tests