frontend-patterns

Frontend-Entwicklungsmuster (Frontend Development Patterns)

Moderne Frontend-Muster für React, Next.js und performante Benutzeroberflächen.

Wann aktivieren

• Erstellen von React-Komponenten (Komposition, Props, Rendering)
• Verwalten von State (useState, useReducer, Zustand, Context)
• Implementieren von Datenabruf (SWR, React Query, Server-Komponenten)
• Optimieren der Leistung (Memoization, Virtualisierung, Code-Splitting)
• Arbeiten mit Formularen (Validierung, kontrollierte Eingaben, Zod-Schemas)
• Umgang mit clientseitigem Routing und Navigation
• Erstellen von zugänglichen, responsiven UI-Mustern

Komponentenmuster (Component Patterns)

Komposition statt Vererbung (Composition Over Inheritance)

// RICHTIG: GUT: Komponentenkomposition
interface CardProps {
  children: React.ReactNode
  variant?: 'default' | 'outlined'
}

export function Card({ children, variant = 'default' }: CardProps) {
  return <div className={`card card-${variant}`}>{children}</div>
}

export function CardHeader({ children }: { children: React.ReactNode }) {
  return <div className="card-header">{children}</div>
}

export function CardBody({ children }: { children: React.ReactNode }) {
  return <div className="card-body">{children}</div>
}

// Verwendung
<Card>
  <CardHeader>Titel</CardHeader>
  <CardBody>Inhalt</CardBody>
</Card>

Zusammengesetzte Komponenten (Compound Components)

interface TabsContextValue {
  activeTab: string
  setActiveTab: (tab: string) => void
}

const TabsContext = createContext<TabsContextValue | undefined>(undefined)

export function Tabs({ children, defaultTab }: {
  children: React.ReactNode
  defaultTab: string
}) {
  const [activeTab, setActiveTab] = useState(defaultTab)

  return (
    <TabsContext.Provider value={{ activeTab, setActiveTab }}>
      {children}
    </TabsContext.Provider>
  )
}

export function TabList({ children }: { children: React.ReactNode }) {
  return <div className="tab-list">{children}</div>
}

export function Tab({ id, children }: { id: string, children: React.ReactNode }) {
  const context = useContext(TabsContext)
  if (!context) throw new Error('Tab muss innerhalb von Tabs verwendet werden')

  return (
    <button
      className={context.activeTab === id ? 'active' : ''}
      onClick={() => context.setActiveTab(id)}
    >
      {children}
    </button>
  )
}

// Verwendung
<Tabs defaultTab="overview">
  <TabList>
    <Tab id="overview">Übersicht</Tab>
    <Tab id="details">Details</Tab>
  </TabList>
</Tabs>

Render-Props-Muster (Render Props Pattern)

interface DataLoaderProps<T> {
  url: string
  children: (data: T | null, loading: boolean, error: Error | null) => React.ReactNode
}

export function DataLoader<T>({ url, children }: DataLoaderProps<T>) {
  const [data, setData] = useState<T | null>(null)
  const [loading, setLoading] = useState(true)
  const [error, setError] = useState<Error | null>(null)

  useEffect(() => {
    fetch(url)
      .then(res => res.json())
      .then(setData)
      .catch(setError)
      .finally(() => setLoading(false))
  }, [url])

  return <>{children(data, loading, error)}</>
}

// Verwendung
<DataLoader<Market[]> url="/api/markets">
  {(markets, loading, error) => {
    if (loading) return <Spinner />
    if (error) return <Error error={error} />
    return <MarketList markets={markets!} />
  }}
</DataLoader>

Muster für benutzerdefinierte Hooks (Custom Hooks Patterns)

State-Management-Hook

export function useToggle(initialValue = false): [boolean, () => void] {
  const [value, setValue] = useState(initialValue)

  const toggle = useCallback(() => {
    setValue(v => !v)
  }, [])

  return [value, toggle]
}

// Verwendung
const [isOpen, toggleOpen] = useToggle()

Asynchroner Datenabruf-Hook

interface UseQueryOptions<T> {
  onSuccess?: (data: T) => void
  onError?: (error: Error) => void
  enabled?: boolean
}

export function useQuery<T>(
  key: string,
  fetcher: () => Promise<T>,
  options?: UseQueryOptions<T>
) {
  const [data, setData] = useState<T | null>(null)
  const [error, setError] = useState<Error | null>(null)
  const [loading, setLoading] = useState(false)

  // Behalte den aktuellsten fetcher/options in refs, damit refetch referenziell
  // stabil bleibt, auch wenn Aufrufer Inline-Funktionen und Objektliterale übergeben.
  // Ohne dies erzeugt jeder Render einen neuen refetch, und der Effekt unten
  // wird nach jeder Statusaktualisierung erneut ausgeführt - eine Endlos-Abruf-Schleife.
  const fetcherRef = useRef(fetcher)
  const optionsRef = useRef(options)
  useEffect(() => {
    fetcherRef.current = fetcher
    optionsRef.current = options
  })

  const refetch = useCallback(async () => {
    setLoading(true)
    setError(null)

    try {
      const result = await fetcherRef.current()
      setData(result)
      optionsRef.current?.onSuccess?.(result)
    } catch (err) {
      const error = err as Error
      setError(error)
      optionsRef.current?.onError?.(error)
    } finally {
      setLoading(false)
    }
  }, [])

  const enabled = options?.enabled !== false

  useEffect(() => {
    if (enabled) {
      refetch()
    }
  }, [key, enabled, refetch])

  return { data, error, loading, refetch }
}

// Verwendung
const { data: markets, loading, error, refetch } = useQuery(
  'markets',
  () => fetch('/api/markets').then(r => r.json()),
  {
    onSuccess: data => console.log('Abgerufen', data.length, 'Märkte'),
    onError: err => console.error('Fehlgeschlagen:', err)
  }
)

Debounce-Hook

export function useDebounce<T>(value: T, delay: number): T {
  const [debouncedValue, setDebouncedValue] = useState<T>(value)

  useEffect(() => {
    const handler = setTimeout(() => {
      setDebouncedValue(value)
    }, delay)

    return () => clearTimeout(handler)
  }, [value, delay])

  return debouncedValue
}

// Verwendung
const [searchQuery, setSearchQuery] = useState('')
const debouncedQuery = useDebounce(searchQuery, 500)

useEffect(() => {
  if (debouncedQuery) {
    performSearch(debouncedQuery)
  }
}, [debouncedQuery])

Muster für State-Management (State Management Patterns)

Context + Reducer-Muster (Context + Reducer Pattern)

interface State {
  markets: Market[]
  selectedMarket: Market | null
  loading: boolean
}

type Action =
  | { type: 'SET_MARKETS'; payload: Market[] }
  | { type: 'SELECT_MARKET'; payload: Market }
  | { type: 'SET_LOADING'; payload: boolean }

function reducer(state: State, action: Action): State {
  switch (action.type) {
    case 'SET_MARKETS':
      return { ...state, markets: action.payload }
    case 'SELECT_MARKET':
      return { ...state, selectedMarket: action.payload }
    case 'SET_LOADING':
      return { ...state, loading: action.payload }
    default:
      return state
  }
}

const MarketContext = createContext<{
  state: State
  dispatch: Dispatch<Action>
} | undefined>(undefined)

export function MarketProvider({ children }: { children: React.ReactNode }) {
  const [state, dispatch] = useReducer(reducer, {
    markets: [],
    selectedMarket: null,
    loading: false
  })

  return (
    <MarketContext.Provider value={{ state, dispatch }}>
      {children}
    </MarketContext.Provider>
  )
}

export function useMarkets() {
  const context = useContext(MarketContext)
  if (!context) throw new Error('useMarkets muss innerhalb von MarketProvider verwendet werden')
  return context
}

Leistungsoptimierung (Performance Optimization)

Memoization

// RICHTIG: useMemo für teure Berechnungen
// Vor dem Sortieren kopieren - Array.prototype.sort mutiert direkt
const sortedMarkets = useMemo(() => {
  return [...markets].sort((a, b) => b.volume - a.volume)
}, [markets])

// RICHTIG: useCallback für Funktionen, die an Kinder übergeben werden
const handleSearch = useCallback((query: string) => {
  setSearchQuery(query)
}, [])

// RICHTIG: React.memo für reine Komponenten
export const MarketCard = React.memo<MarketCardProps>(({ market }) => {
  return (
    <div className="market-card">
      <h3>{market.name}</h3>
      <p>{market.description}</p>
    </div>
  )
})

Code-Splitting & Lazy Loading

import { lazy, Suspense } from 'react'

// RICHTIG: Lazy Load für schwere Komponenten
const HeavyChart = lazy(() => import('./HeavyChart'))
const ThreeJsBackground = lazy(() => import('./ThreeJsBackground'))

export function Dashboard() {
  return (
    <div>
      <Suspense fallback={<ChartSkeleton />}>
        <HeavyChart data={data} />
      </Suspense>

      <Suspense fallback={null}>
        <ThreeJsBackground />
      </Suspense>
    </div>
  )
}

Virtualisierung für lange Listen (Virtualization for Long Lists)

import { useVirtualizer } from '@tanstack/react-virtual'

export function VirtualMarketList({ markets }: { markets: Market[] }) {
  const parentRef = useRef<HTMLDivElement>(null)

  const virtualizer = useVirtualizer({
    count: markets.length,
    getScrollElement: () => parentRef.current,
    estimateSize: () => 100,  // Geschätzte Zeilenhöhe
    overscan: 5  // Zusätzliche Elemente zum Rendern
  })

  return (
    <div ref={parentRef} style={{ height: '600px', overflow: 'auto' }}>
      <div
        style={{
          height: `${virtualizer.getTotalSize()}px`,
          position: 'relative'
        }}
      >
        {virtualizer.getVirtualItems().map(virtualRow => (
          <div
            key={virtualRow.index}
            style={{
              position: 'absolute',
              top: 0,
              left: 0,
              width: '100%',
              height: `${virtualRow.size}px`,
              transform: `translateY(${virtualRow.start}px)`
            }}
          >
            <MarketCard market={markets[virtualRow.index]} />
          </div>
        ))}
      </div>
    </div>
  )
}

Muster für Formularverarbeitung (Form Handling Patterns)

Kontrolliertes Formular mit Validierung (Controlled Form with Validation)

interface FormData {
  name: string
  description: string
  endDate: string
}

interface FormErrors {
  name?: string
  description?: string
  endDate?: string
}

export function CreateMarketForm() {
  const [formData, setFormData] = useState<FormData>({
    name: '',
    description: '',
    endDate: ''
  })

  const [errors, setErrors] = useState<FormErrors>({}

  const validate = (): boolean => {
    const newErrors: FormErrors = {}

    if (!formData.name.trim()) {
      newErrors.name = 'Name ist erforderlich'
    } else if (formData.name.length > 200) {
      newErrors.name = 'Name darf maximal 200 Zeichen lang sein'
    }

    if (!formData.description.trim()) {
      newErrors.description = 'Beschreibung ist erforderlich'
    }

    if (!formData.endDate) {
      newErrors.endDate = 'Enddatum ist erforderlich'
    }

    setErrors(newErrors)
    return Object.keys(newErrors).length === 0
  }

  const handleSubmit = async (e: React.FormEvent) => {
    e.preventDefault()

    if (!validate()) return

    try {
      await createMarket(formData)
      // Erfolgsbehandlung
    } catch (error) {
      // Fehlerbehandlung
    }
  }

  return (
    <form onSubmit={handleSubmit}>
      <input
        value={formData.name}
        onChange={e => setFormData(prev => ({ ...prev, name: e.target.value }))}
        placeholder="Marktname"
      />
      {errors.name && <span className="error">{errors.name}</span>}

      {/* Weitere Felder */}

      <button type="submit">Markt erstellen</button>
    </form>
  )
}

Fehlergrenzen-Muster (Error Boundary Pattern)

interface ErrorBoundaryState {
  hasError: boolean
  error: Error | null
}

export class ErrorBoundary extends React.Component<
  { children: React.ReactNode },
  ErrorBoundaryState
> {
  state: ErrorBoundaryState = {
    hasError: false,
    error: null
  }

  static getDerivedStateFromError(error: Error): ErrorBoundaryState {
    return { hasError: true, error }
  }

  componentDidCatch(error: Error, errorInfo: React.ErrorInfo) {
    console.error('Fehlergrenze gefangen:', error, errorInfo)
  }

  render() {
    if (this.state.hasError) {
      return (
        <div className="error-fallback">
          <h2>Etwas ist schiefgelaufen</h2>
          <p>{this.state.error?.message}</p>
          <button onClick={() => this.setState({ hasError: false })}>
            Erneut versuchen
          </button>
        </div>
      )
    }

    return this.props.children
  }
}

// Verwendung
<ErrorBoundary>
  <App />
</ErrorBoundary>

Animationsmuster (Animation Patterns)

Framer Motion Animationen

import { motion, AnimatePresence } from 'framer-motion'

// RICHTIG: Listenanimationen
export function AnimatedMarketList({ markets }: { markets: Market[] }) {
  return (
    <AnimatePresence>
      {markets.map(market => (
        <motion.div
          key={market.id}
          initial={{ opacity: 0, y: 20 }}
          animate={{ opacity: 1, y: 0 }}
          exit={{ opacity: 0, y: -20 }}
          transition={{ duration: 0.3 }}
        >
          <MarketCard market={market} />
        </motion.div>
      ))}
    </AnimatePresence>
  )
}

// RICHTIG: Modal-Animationen
export function Modal({ isOpen, onClose, children }: ModalProps) {
  return (
    <AnimatePresence>
      {isOpen && (
        <>
          <motion.div
            className="modal-overlay"
            initial={{ opacity: 0 }}
            animate={{ opacity: 1 }}
            exit={{ opacity: 0 }}
            onClick={onClose}
          />
          <motion.div
            className="modal-content"
            initial={{ opacity: 0, scale: 0.9, y: 20 }}
            animate={{ opacity: 1, scale: 1, y: 0 }}
            exit={{ opacity: 0, scale: 0.9, y: 20 }}
          >
            {children}
          </motion.div>
        </>
      )}
    </AnimatePresence>
  )
}

Barrierefreiheitsmuster (Accessibility Patterns)

Tastaturnavigation (Keyboard Navigation)

export function Dropdown({ options, onSelect }: DropdownProps) {
  const [isOpen, setIsOpen] = useState(false)
  const [activeIndex, setActiveIndex] = useState(0)

  const handleKeyDown = (e: React.KeyboardEvent) => {
    switch (e.key) {
      case 'ArrowDown':
        e.preventDefault()
        setActiveIndex(i => Math.min(i + 1, options.length - 1))
        break
      case 'ArrowUp':
        e.preventDefault()
        setActiveIndex(i => Math.max(i - 1, 0))
        break
      case 'Enter':
        e.preventDefault()
        onSelect(options[activeIndex])
        break
      case 'Escape':
        e.preventDefault()
        setIsOpen(false)
        break
    }
  }

  // ... weitere Implementierung
}