Frontend Patterns

Component Design

Composition over Inheritance

// DOGRU: Composition
function Card({ children, header }: { children: ReactNode; header: ReactNode }) {
  return (
    <div className="card">
      <div className="card-header">{header}</div>
      <div className="card-body">{children}</div>
    </div>
  );
}

// Kullanim
<Card header={<h2>Title</h2>}>
  <p>Content here</p>
</Card>

Container/Presenter Pattern

// Container: Data fetching + logic
function UserListContainer() {
  const { data, isLoading } = useQuery(['users'], fetchUsers);
  if (isLoading) return <Skeleton />;
  return <UserList users={data} />;
}

// Presenter: Pure rendering
function UserList({ users }: { users: User[] }) {
  return (
    <ul>
      {users.map(u => <UserItem key={u.id} user={u} />)}
    </ul>
  );
}

State Management

Cozum	Ne Zaman	Karmasiklik
useState	Local component state	Dusuk
useReducer	Complex local state	Orta
Context	Theme, auth, locale	Dusuk-Orta
Zustand	Global client state	Orta
React Query	Server state	Orta
URL params	Navigation state	Dusuk

Performance

// React.memo: Expensive render onleme
const ExpensiveList = React.memo(({ items }: { items: Item[] }) => (
  <ul>{items.map(i => <ListItem key={i.id} item={i} />)}</ul>
));

// useMemo: Expensive hesaplama cache
const filtered = useMemo(
  () => items.filter(i => i.status === status),
  [items, status]
);

// useCallback: Referans stabilitesi
const handleClick = useCallback((id: string) => {
  setSelected(id);
}, []);

Next.js Patterns

Feature	Ne Zaman
Server Component	Data fetch, no interactivity
Client Component	onClick, useState, useEffect
Route Handler	API endpoint
Middleware	Auth, redirect, rewrite
Streaming	Buyuk data, progressive rendering

shadcn/ui Best Practices

// Theme config: globals.css'te CSS variable kullan
// shadcn/ui dark mode: class strategy (Tailwind darkMode: 'class')

// Component override: cn() ile extend et, fork etme
import { Button } from '@/components/ui/button'
<Button variant="outline" className={cn('custom-class', className)} />

// Compose, override etme:
function SubmitButton({ children, ...props }: ButtonProps) {
  return <Button type="submit" variant="default" {...props}>{children}</Button>
}

// A11y: shadcn radix tabanli, otomatik ARIA ama kontrol et
// Dark mode: CSS variable'lar otomatik switch eder

Performance Budget

Metrik	Esik	Olcum
LCP (Largest Contentful Paint)	< 2.5s	Core Web Vital
CLS (Cumulative Layout Shift)	< 0.1	Core Web Vital
INP (Interaction to Next Paint)	< 200ms	Core Web Vital
FCP (First Contentful Paint)	< 1.8s	Lighthouse
TTI (Time to Interactive)	< 3.8s	Lighthouse
Total JS bundle	< 200KB gzipped	Build analiz

React Performance Top 10

1. React.memo sadece gercekten expensive render'larda
2. useMemo/useCallback sadece referans stability gerektiginde
3. Code splitting: React.lazy() + Suspense route bazli
4. Image optimization: next/image, lazy loading, WebP/AVIF
5. Virtual scroll: 100+ item listede @tanstack/virtual
6. Debounce: Arama input'unda 300ms debounce
7. Skeleton UI: Loading state icin layout shift onleme
8. Bundle analyze: @next/bundle-analyzer ile kontrol
9. Prefetch: <Link prefetch> kritik navigation'larda
10. Server Component: Default RSC, client sadece interactive icin

Anti-Patterns

Anti-Pattern	Dogru Yol
Prop drilling (5+ level)	Context veya state library
useEffect for derived state	useMemo kullan
Index as key	Unique ID kullan
Premature optimization	Profiler ile olc, sonra optimize et