affaan-m/everything-claude-code/frontend-patterns

// PASS: GOOD: Component composition
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>
}
// Usage
<Card>
  <CardHeader>Title</CardHeader>
  <CardBody>Content</CardBody>
</Card>

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 must be used within Tabs')
  return (
    <button
      className={context.activeTab === id ? 'active' : ''}
      onClick={() => context.setActiveTab(id)}
    >
      {children}
    </button>
  )
}
// Usage
<Tabs defaultTab="overview">
  <TabList>
    <Tab id="overview">Overview</Tab>
    <Tab id="details">Details</Tab>
  </TabList>
</Tabs>

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

export function useToggle(initialValue = false): [boolean, () => void] {
  const [value, setValue] = useState(initialValue)
  const toggle = useCallback(() => {
    setValue(v => !v)
  }, [])
  return [value, toggle]
}
// Usage
const [isOpen, toggleOpen] = useToggle()

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)
  // Keep the latest fetcher/options in refs so refetch stays referentially
  // stable even when callers pass inline functions and object literals.
  // Without this, every render creates a new refetch, and the effect below
  // re-runs after each state update - an infinite fetch loop.
  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 }
}
// Usage
const { data: markets, loading, error, refetch } = useQuery(
  'markets',
  () => fetch('/api/markets').then(r => r.json()),
  {
    onSuccess: data => console.log('Fetched', data.length, 'markets'),
    onError: err => console.error('Failed:', err)
  }
)

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
}
// Usage
const [searchQuery, setSearchQuery] = useState('')
const debouncedQuery = useDebounce(searchQuery, 500)
useEffect(() => {
  if (debouncedQuery) {
    performSearch(debouncedQuery)
  }
}, [debouncedQuery])

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 must be used within MarketProvider')
  return context
}

// PASS: useMemo for expensive computations
// Copy before sorting - Array.prototype.sort mutates in place
const sortedMarkets = useMemo(() => {
  return [...markets].sort((a, b) => b.volume - a.volume)
}, [markets])
// PASS: useCallback for functions passed to children
const handleSearch = useCallback((query: string) => {
  setSearchQuery(query)
}, [])
// PASS: React.memo for pure components
export const MarketCard = React.memo<MarketCardProps>(({ market }) => {
  return (
    <div className="market-card">
      <h3>{market.name}</h3>
      <p>{market.description}</p>
    </div>
  )
})

import { lazy, Suspense } from 'react'
// PASS: Lazy load heavy components
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>
  )
}

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,  // Estimated row height
    overscan: 5  // Extra items to render
  })
  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>
  )
}

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 is required'
    } else if (formData.name.length > 200) {
      newErrors.name = 'Name must be under 200 characters'
    }
    if (!formData.description.trim()) {
      newErrors.description = 'Description is required'
    }
    if (!formData.endDate) {
      newErrors.endDate = 'End date is required'
    }
    setErrors(newErrors)
    return Object.keys(newErrors).length === 0
  }
  const handleSubmit = async (e: React.FormEvent) => {
    e.preventDefault()
    if (!validate()) return
    try {
      await createMarket(formData)
      // Success handling
    } catch (error) {
      // Error handling
    }
  }
  return (
    <form onSubmit={handleSubmit}>
      <input
        value={formData.name}
        onChange={e => setFormData(prev => ({ ...prev, name: e.target.value }))}
        placeholder="Market name"
      />
      {errors.name && <span className="error">{errors.name}</span>}
      {/* Other fields */}
      <button type="submit">Create Market</button>
    </form>
  )
}

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('Error boundary caught:', error, errorInfo)
  }
  render() {
    if (this.state.hasError) {
      return (
        <div className="error-fallback">
          <h2>Something went wrong</h2>
          <p>{this.state.error?.message}</p>
          <button onClick={() => this.setState({ hasError: false })}>
            Try again
          </button>
        </div>
      )
    }
    return this.props.children
  }
}