Frontend Development Patterns
Modern frontend patterns for React, Next.js, and performant user interfaces.
Component Patterns
Composition Over Inheritance
// ✅ 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>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 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>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)}</>
}
// Usage
<DataLoader<Market[]> url="/api/markets">
{(markets, loading, error) => {
if (loading) return <Spinner />
if (error) return <Error error={error} />
return <MarketList markets={markets!} />
}}
</DataLoader>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]
}
// Usage
const [isOpen, toggleOpen] = useToggle()Async Data Fetching 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)
const refetch = useCallback(async () => {
setLoading(true)
setError(null)
try {
const result = await fetcher()
setData(result)
options?.onSuccess?.(result)
} catch (err) {
const error = err as Error
setError(error)
options?.onError?.(error)
} finally {
setLoading(false)
}
}, [fetcher, options])
useEffect(() => {
if (options?.enabled !== false) {
refetch()
}
}, [key, refetch, options?.enabled])
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)
}
)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
}
// Usage
const [searchQuery, setSearchQuery] = useState('')
const debouncedQuery = useDebounce(searchQuery, 500)
useEffect(() => {
if (debouncedQuery) {
performSearch(debouncedQuery)
}
}, [debouncedQuery])State Management Patterns
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 must be used within MarketProvider')
return context
}Performance Optimization
Memoization
// ✅ useMemo for expensive computations
const sortedMarkets = useMemo(() => {
return markets.sort((a, b) => b.volume - a.volume)
}, [markets])
// ✅ useCallback for functions passed to children
const handleSearch = useCallback((query: string) => {
setSearchQuery(query)
}, [])
// ✅ 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>
)
})Code Splitting & Lazy Loading
import { lazy, Suspense } from 'react'
// ✅ 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>
)
}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, // 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>
)
}Form Handling Patterns
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 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>
)
}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('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
}
}
// Usage
<ErrorBoundary>
<App />
</ErrorBoundary>Animation Patterns
Framer Motion Animations
import { motion, AnimatePresence } from 'framer-motion'
// ✅ List animations
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>
)
}
// ✅ Modal animations
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>
)
}Accessibility Patterns
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])
setIsOpen(false)
break
case 'Escape':
setIsOpen(false)
break
}
}
return (
<div
role="combobox"
aria-expanded={isOpen}
aria-haspopup="listbox"
onKeyDown={handleKeyDown}
>
{/* Dropdown implementation */}
</div>
)
}Focus Management
export function Modal({ isOpen, onClose, children }: ModalProps) {
const modalRef = useRef<HTMLDivElement>(null)
const previousFocusRef = useRef<HTMLElement | null>(null)
useEffect(() => {
if (isOpen) {
// Save currently focused element
previousFocusRef.current = document.activeElement as HTMLElement
// Focus modal
modalRef.current?.focus()
} else {
// Restore focus when closing
previousFocusRef.current?.focus()
}
}, [isOpen])
return isOpen ? (
<div
ref={modalRef}
role="dialog"
aria-modal="true"
tabIndex={-1}
onKeyDown={e => e.key === 'Escape' && onClose()}
>
{children}
</div>
) : null
}Remember: Modern frontend patterns enable maintainable, performant user interfaces. Choose patterns that fit your project complexity.
When to Use
This skill is applicable to execute the workflow or actions described in the overview.
Limitations
- Use this skill only when the task clearly matches the scope described above.
- Do not treat the output as a substitute for environment-specific validation, testing, or expert review.
- Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.