Modern React 19+ patterns with TypeScript including function components, hooks, state management, TanStack Query integration, form handling with Zod, error boundaries, and performance optimization. Use when building React applications, implementing components, or setting up state management.
Modern React 19+ patterns with TypeScript for building robust frontend applications.
interface UserCardProps {
user: User;
onSelect?: (user: User) => void;
className?: string;
}
export function UserCard({ user, onSelect, className }: UserCardProps) {
return (
<div className={className} onClick={() => onSelect?.(user)}>
<h3>{user.name}</h3>
<p>{user.email}</p>
</div>
);
}
interface ContainerProps {
children: React.ReactNode;
title?: string;
}
export function Container({ children, title }: ContainerProps) {
return (
<div className="container">
{title && <h2>{title}</h2>}
{children}
</div>
);
}
interface ListProps<T> {
items: T[];
renderItem: (item: T) => React.ReactNode;
keyExtractor: (item: T) => string;
}
export function List<T>({ items, renderItem, keyExtractor }: ListProps<T>) {
return (
<ul>
{items.map(item => (
<li key={keyExtractor(item)}>{renderItem(item)}</li>
))}
</ul>
);
}
interface UseCounterOptions {
initialValue?: number;
min?: number;
max?: number;
}
export function useCounter({ initialValue = 0, min, max }: UseCounterOptions = {}) {
const [count, setCount] = useState(initialValue);
const increment = useCallback(() => {
setCount(c => (max !== undefined ? Math.min(c + 1, max) : c + 1));
}, [max]);
const decrement = useCallback(() => {
setCount(c => (min !== undefined ? Math.max(c - 1, min) : c - 1));
}, [min]);
const reset = useCallback(() => setCount(initialValue), [initialValue]);
return { count, increment, decrement, reset };
}
interface UseFetchResult<T> {
data: T | null;
loading: boolean;
error: Error | null;
refetch: () => Promise<void>;
}
export function useFetch<T>(url: string): UseFetchResult<T> {
const [data, setData] = useState<T | null>(null);
const [loading, setLoading] = useState(true);
const [error, setError] = useState<Error | null>(null);
const fetchData = useCallback(async () => {
setLoading(true);
setError(null);
try {
const response = await fetch(url);
if (!response.ok) throw new Error(`HTTP ${response.status}`);
const result = await response.json();
setData(result);
} catch (e) {
setError(e instanceof Error ? e : new Error('Unknown error'));
} finally {
setLoading(false);
}
}, [url]);
useEffect(() => {
fetchData();
}, [fetchData]);
return { data, loading, error, refetch: fetchData };
}
interface AuthContextValue {
user: User | null;
login: (credentials: Credentials) => Promise<void>;
logout: () => void;
isAuthenticated: boolean;
}
const AuthContext = createContext<AuthContextValue | null>(null);
export function AuthProvider({ children }: { children: React.ReactNode }) {
const [user, setUser] = useState<User | null>(null);
const login = async (credentials: Credentials) => {
const user = await authService.login(credentials);
setUser(user);
};
const logout = () => {
authService.logout();
setUser(null);
};
return (
<AuthContext.Provider
value={{ user, login, logout, isAuthenticated: !!user }}
>
{children}
</AuthContext.Provider>
);
}
export function useAuth() {
const context = useContext(AuthContext);
if (!context) throw new Error('useAuth must be used within AuthProvider');
return context;
}
interface StoreState {
count: number;
users: User[];
increment: () => void;
setUsers: (users: User[]) => void;
}
export const useStore = create<StoreState>((set) => ({
count: 0,
users: [],
increment: () => set((state) => ({ count: state.count + 1 })),
setUsers: (users) => set({ users }),
}));
export function useUser(userId: string) {
return useQuery({
queryKey: ['user', userId],
queryFn: () => api.getUser(userId),
staleTime: 5 * 60 * 1000, // 5 minutes
});
}
// Usage
function UserProfile({ userId }: { userId: string }) {
const { data: user, isLoading, error } = useUser(userId);
if (isLoading) return <Spinner />;
if (error) return <ErrorMessage error={error} />;
if (!user) return <NotFound />;
return <UserCard user={user} />;
}
export function useUpdateUser() {
const queryClient = useQueryClient();
return useMutation({
mutationFn: (data: UpdateUserInput) => api.updateUser(data),
onMutate: async (newData) => {
await queryClient.cancelQueries({ queryKey: ['user', newData.id] });
const previous = queryClient.getQueryData(['user', newData.id]);
queryClient.setQueryData(['user', newData.id], (old: User) => ({
...old,
...newData,
}));
return { previous };
},
onError: (err, newData, context) => {
queryClient.setQueryData(['user', newData.id], context?.previous);
},
onSettled: (data, error, variables) => {
queryClient.invalidateQueries({ queryKey: ['user', variables.id] });
},
});
}
const userSchema = z.object({
name: z.string().min(2, 'Name must be at least 2 characters'),
email: z.string().email('Invalid email'),
age: z.number().min(18, 'Must be 18 or older'),
});
type UserFormData = z.infer<typeof userSchema>;
export function UserForm({ onSubmit }: { onSubmit: (data: UserFormData) => void }) {
const {
register,
handleSubmit,
formState: { errors, isSubmitting },
} = useForm<UserFormData>({
resolver: zodResolver(userSchema),
});
return (
<form onSubmit={handleSubmit(onSubmit)}>
<input {...register('name')} placeholder="Name" />
{errors.name && <span>{errors.name.message}</span>}
<input {...register('email')} type="email" placeholder="Email" />
{errors.email && <span>{errors.email.message}</span>}
<input {...register('age', { valueAsNumber: true })} type="number" />
{errors.age && <span>{errors.age.message}</span>}
<button type="submit" disabled={isSubmitting}>
{isSubmitting ? 'Saving...' : 'Save'}
</button>
</form>
);
}
interface ErrorBoundaryProps {
children: React.ReactNode;
fallback?: React.ReactNode;
}
interface ErrorBoundaryState {
hasError: boolean;
error: Error | null;
}
export class ErrorBoundary extends Component<ErrorBoundaryProps, ErrorBoundaryState> {
state: ErrorBoundaryState = { hasError: false, error: null };
static getDerivedStateFromError(error: Error): ErrorBoundaryState {
return { hasError: true, error };
}
componentDidCatch(error: Error, errorInfo: ErrorInfo) {
console.error('ErrorBoundary caught:', error, errorInfo);
}
render() {
if (this.state.hasError) {
return this.props.fallback ?? <DefaultErrorFallback error={this.state.error} />;
}
return this.props.children;
}
}
// Memoize expensive computations
const sortedUsers = useMemo(() => {
return users.sort((a, b) => a.name.localeCompare(b.name));
}, [users]);
// Memoize callbacks
const handleClick = useCallback((id: string) => {
setSelectedId(id);
}, []);
// Memoize components
const MemoizedUserCard = memo(UserCard);
// Lazy load components
const AdminPanel = lazy(() => import('./AdminPanel'));
function App() {
return (
<Suspense fallback={<Spinner />}>
<AdminPanel />
</Suspense>
);
}
src/
├── components/
│ ├── common/ # Shared components
│ │ ├── Button/
│ │ │ ├── Button.tsx
│ │ │ ├── Button.test.tsx
│ │ │ └── index.ts
│ │ └── Input/
│ ├── features/ # Feature components
│ │ ├── auth/
│ │ └── users/
│ └── layout/ # Layout components
├── hooks/ # Custom hooks
├── stores/ # State management
├── services/ # API services
├── types/ # TypeScript types
├── utils/ # Utilities
└── App.tsx
interface ApiResponse<T> {
data: T;
message: string;
success: boolean;
}
interface PaginatedResponse<T> {
items: T[];
total: number;
page: number;
pageSize: number;
}
type ClickHandler = React.MouseEventHandler<HTMLButtonElement>;
type ChangeHandler = React.ChangeEventHandler<HTMLInputElement>;
type SubmitHandler = React.FormEventHandler<HTMLFormElement>;
React + TypeScript patterns for modern frontend development
The React Compiler automatically optimizes components for performance. Write code that works well with it:
Best Practices:
"use no memo" while refactoringExample - Pure Component:
// ✅ Compiler-friendly - pure function
function UserCard({ user }: { user: User }) {
const displayName = `${user.firstName} ${user.lastName}`
const isVIP = user.points > 1000
return (
<div>
<h2>{displayName}</h2>
{isVIP && <Badge>VIP</Badge>}
</div>
)
}
// ❌ Avoid - unnecessary effects
function UserCard({ user }: { user: User }) {
const [displayName, setDisplayName] = useState('')
useEffect(() => {
setDisplayName(`${user.firstName} ${user.lastName}`)
}, [user])
return <div><h2>{displayName}</h2></div>
}
Verification:
Opt-Out When Needed:
'use no memo'
// Component code that can't be optimized yet
function ProblematicComponent() {
// ... code with compiler issues
}
For SPA mutations, choose one approach per feature:
<form action={fn}>, useActionState, useOptimisticuseMutationDon't duplicate logic between both approaches.
Best for:
Basic Action:
async function createTodoAction(formData: FormData) {
const text = formData.get('text') as string
// Validation
if (!text || text.length < 3) {
return { error: 'Text must be at least 3 characters' }
}
// API call
await api.post('/todos', { text })
return { success: true }
}
// Component
function TodoForm() {
return (
<form action={createTodoAction}>
<input name="text" required />
<button type="submit">Add Todo</button>
</form>
)
}
With State (useActionState):
import { useActionState } from 'react'
function TodoForm() {
const [state, formAction, isPending] = useActionState(
createTodoAction,
{ error: null, success: false }
)
return (
<form action={formAction}>
{state.error && <ErrorMessage>{state.error}</ErrorMessage>}
<input name="text" required />
<button type="submit" disabled={isPending}>
{isPending ? 'Adding...' : 'Add Todo'}
</button>
</form>
)
}
With Optimistic Updates (useOptimistic):
import { useOptimistic } from 'react'
function TaskList({ initialTodos }: { initialTodos: Todo[] }) {
const [optimisticTodos, addOptimisticTodo] = useOptimistic(
initialTodos,
(state, newTodo: string) => [
...state,
{ id: `temp-${Date.now()}`, text: newTodo, completed: false }
]
)
async function handleSubmit(formData: FormData) {
const text = formData.get('text') as string
addOptimisticTodo(text)
await createTodoAction(formData)
}
return (
<>
<ul>
{optimisticTodos.map(todo => (
<li key={todo.id} style={{ opacity: todo.id.startsWith('temp-') ? 0.5 : 1 }}>
{todo.text}
</li>
))}
</ul>
<form action={handleSubmit}>
<input name="text" required />
<button type="submit">Add</button>
</form>
</>
)
}
The use hook unwraps Promises and Context, enabling new patterns.
With Promises:
import { use, Suspense } from 'react'
function UserProfile({ userPromise }: { userPromise: Promise<User> }) {
const user = use(userPromise)
return <div>{user.name}</div>
}
// Usage
function App() {
const userPromise = fetchUser(1)
return (
<Suspense fallback={<Spinner />}>
<UserProfile userPromise={userPromise} />
</Suspense>
)
}
With Context:
import { use, createContext } from 'react'
const ThemeContext = createContext<string>('light')
function Button() {
const theme = use(ThemeContext)
return <button className={theme}>Click me</button>
}
When to Use:
use shines when you already have a Promise from a parent componentCompound Components:
// ✅ Good - composable, flexible
<Card>
<Card.Header>
<Card.Title>Dashboard</Card.Title>
</Card.Header>
<Card.Content>
{/* content */}
</Card.Content>
</Card>
// Implementation
function Card({ children }: { children: React.ReactNode }) {
return <div className="card">{children}</div>
}
Card.Header = function CardHeader({ children }: { children: React.ReactNode }) {
return <header className="card-header">{children}</header>
}
Card.Title = function CardTitle({ children }: { children: React.ReactNode }) {
return <h2 className="card-title">{children}</h2>
}
Card.Content = function CardContent({ children }: { children: React.ReactNode }) {
return <div className="card-content">{children}</div>
}
| Scenario | Recommendation | |----------|---------------| | Form submission with validation | React Actions | | Button click mutation | TanStack Query | | Needs optimistic updates + rollback | TanStack Query | | Integrates with existing cache | TanStack Query | | SSR/RSC application | React Actions | | SPA with complex data flow | TanStack Query | | Simple CRUD with forms | React Actions |
Rule of Thumb: For SPAs with TanStack Query already in use, prefer Query mutations for consistency. Only use Actions for form-heavy features where the form-centric API is beneficial.
XSS Prevention:
// ❌ Dangerous
<div dangerouslySetInnerHTML={{ __html: userInput }} />
// ✅ Sanitize first
import DOMPurify from 'dompurify'
<div dangerouslySetInnerHTML={{
__html: DOMPurify.sanitize(userInput)
}} />
// ✅ Best - avoid dangerouslySetInnerHTML
<div>{userInput}</div>
Environment Variables:
// ❌ Exposes secrets
const API_KEY = process.env.VITE_SECRET_API_KEY
// ✅ Separate public/private
// Public (can be in client): VITE_PUBLIC_API_URL
// Private (server only): SECRET_API_KEY
Search for places (restaurants, cafes, etc.) via Google Places API proxy on localhost.
Interact with GitHub using the `gh` CLI. Use `gh issue`, `gh pr`, `gh run`, and `gh api` for issues, PRs, CI runs, and advanced queries.
Create or update AgentSkills. Use when designing, structuring, or packaging skills with scripts, references, and assets.
Start voice calls via the OpenClaw voice-call plugin.
Notion API for creating and managing pages, databases, and blocks.
Gemini CLI for one-shot Q&A, summaries, and generation.
Category:developer