Frontend patterns — React component composition, state management (useState/useReducer/Zustand/Jotai), Next.js App Router, performance optimization (memo/useMemo/lazy), form handling, error boundaries, and TypeScript patterns.
From clarcnpx claudepluginhub marvinrichter/clarc --plugin clarcThis skill uses the workspace's default tool permissions.
Designs and optimizes AI agent action spaces, tool definitions, observation formats, error recovery, and context for higher task completion rates.
Enables AI agents to execute x402 payments with per-task budgets, spending controls, and non-custodial wallets via MCP tools. Use when agents pay for APIs, services, or other agents.
Compares coding agents like Claude Code and Aider on custom YAML-defined codebase tasks using git worktrees, measuring pass rate, cost, time, and consistency.
Modern frontend patterns for React, Next.js, and performant user interfaces.
// ✅ 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>
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)
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)
}
)
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
}
// ✅ 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>
)
})
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>
)
}
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
}
}
// Usage
<ErrorBoundary>
<App />
</ErrorBoundary>
Remember: Modern frontend patterns enable maintainable, performant user interfaces. Choose patterns that fit your project complexity.