Advanced React composition patterns, hooks architecture, Server Component patterns, and Next.js App Router patterns for building elegant, maintainable UIs.
// Like Shadcn's Tabs — children share implicit state via Context
const TabsContext = createContext<{ active: string; setActive: (v: string) => void } | null>(null)
function Tabs({ defaultValue, children }: { defaultValue: string; children: ReactNode }) {
const [active, setActive] = useState(defaultValue)
return (
<TabsContext.Provider value={{ active, setActive }}>
<div role="tablist">{children}</div>
</TabsContext.Provider>
)
}
function Tab({ value, children }: { value: string; children: ReactNode }) {
const ctx = useContext(TabsContext)!
return (
<button role="tab" aria-selected={ctx.active === value} onClick={() => ctx.setActive(value)}>
{children}
</button>
)
}
function TabPanel({ value, children }: { value: string; children: ReactNode }) {
const ctx = useContext(TabsContext)!
if (ctx.active !== value) return null
return <div role="tabpanel">{children}</div>
}
// Usage — clean, composable API
<Tabs defaultValue="overview">
<Tab value="overview">Overview</Tab>
<Tab value="entries">Entries</Tab>
<TabPanel value="overview"><Overview /></TabPanel>
<TabPanel value="entries"><EntryList /></TabPanel>
</Tabs>
// <Button as="a" href="/"> renders an anchor with button styles
type PolymorphicProps<E extends ElementType, P = {}> = P &
Omit<ComponentPropsWithoutRef<E>, keyof P> & { as?: E }
function Button<E extends ElementType = 'button'>({
as, children, ...props
}: PolymorphicProps<E, { variant?: 'primary' | 'ghost' }>) {
const Component = as || 'button'
return <Component className={cn('btn', props.variant)} {...props}>{children}</Component>
}
// Type-safe: <Button as="a" href="/"> works, <Button as="a" onClick={}> also works
// <Button as="a" disabled> → TypeScript error (anchor doesn't have disabled)
// Works both ways — controlled if value/onChange provided, uncontrolled otherwise
function SearchInput({ value: controlledValue, onChange, defaultValue = '' }: {
value?: string
onChange?: (value: string) => void
defaultValue?: string
}) {
const [internalValue, setInternalValue] = useState(defaultValue)
const isControlled = controlledValue !== undefined
const value = isControlled ? controlledValue : internalValue
const handleChange = (e: ChangeEvent<HTMLInputElement>) => {
if (!isControlled) setInternalValue(e.target.value)
onChange?.(e.target.value)
}
return <input value={value} onChange={handleChange} />
}
type ChallengeState =
| { status: 'idle' }
| { status: 'loading' }
| { status: 'active'; startedAt: Date; timeRemaining: number }
| { status: 'judging'; submittedAt: Date }
| { status: 'complete'; results: Result[] }
| { status: 'error'; message: string }
type ChallengeAction =
| { type: 'START' }
| { type: 'TICK'; remaining: number }
| { type: 'SUBMIT'; submittedAt: Date }
| { type: 'RESULTS'; results: Result[] }
| { type: 'ERROR'; message: string }
function challengeReducer(state: ChallengeState, action: ChallengeAction): ChallengeState {
switch (action.type) {
case 'START': return { status: 'active', startedAt: new Date(), timeRemaining: 1800 }
case 'TICK': return state.status === 'active'
? { ...state, timeRemaining: action.remaining } : state
case 'SUBMIT': return { status: 'judging', submittedAt: action.submittedAt }
case 'RESULTS': return { status: 'complete', results: action.results }
case 'ERROR': return { status: 'error', message: action.message }
}
}
// TypeScript exhaustiveness: add a case for every action type or get a compile error
// Subscribe to external data source without useEffect
function useRealtimeLeaderboard(weightClass: string) {
const subscribe = useCallback((callback: () => void) => {
const channel = supabase.channel(`leaderboard:${weightClass}`)
.on('postgres_changes', { event: '*', schema: 'public', table: 'agent_ratings' }, callback)
.subscribe()
return () => { channel.unsubscribe() }
}, [weightClass])
const getSnapshot = useCallback(() => leaderboardCache.get(weightClass), [weightClass])
return useSyncExternalStore(subscribe, getSnapshot)
}
// Server → Client → Server (server component as children of client component)
// layout.tsx (Server)
export default function Layout({ children }: { children: ReactNode }) {
return (
<ClientSidebar> {/* Client: handles toggle state */}
<ServerNavLinks /> {/* Server: fetches nav data from DB */}
</ClientSidebar>
)
}
// children are server-rendered, passed as serialized React tree to client component
// Page loads immediately, slow data streams in
export default function ChallengePage({ params }: { params: { id: string } }) {
return (
<div>
<ChallengeHeader id={params.id} /> {/* Fast — renders immediately */}
<Suspense fallback={<EntriesSkeleton />}>
<ChallengeEntries id={params.id} /> {/* Slow — streams when ready */}
</Suspense>
<Suspense fallback={<LeaderboardSkeleton />}>
<WeightClassLeaderboard /> {/* Independent — streams separately */}
</Suspense>
</div>
)
}
// lib/server-utils.ts
import 'server-only' // Throws at build time if imported from client component
export async function getSecretConfig() {
return { apiKey: process.env.ANTHROPIC_API_KEY }
}
// If a client component imports this → build error, not runtime leak
'use client'
import { useOptimistic, useTransition } from 'react'
function VoteButton({ entryId, currentVotes }: { entryId: string; currentVotes: number }) {
const [optimisticVotes, addOptimistic] = useOptimistic(
currentVotes,
(current, delta: number) => current + delta
)
const [isPending, startTransition] = useTransition()
return (
<button
disabled={isPending}
onClick={() => {
addOptimistic(1) // Immediately show +1
startTransition(async () => {
await voteForEntry(entryId) // Server Action — may fail
// If fails, optimistic update auto-reverts
})
}}
>
⬆ {optimisticVotes}
</button>
)
}
// ❌ Spinner — user sees blank then sudden content (jarring)
if (loading) return <Spinner />
// ✅ Skeleton — user sees content shape, perceives faster load
if (loading) return (
<div className="space-y-4">
<div className="h-8 w-48 bg-muted animate-pulse rounded" />
<div className="h-4 w-full bg-muted animate-pulse rounded" />
<div className="h-4 w-3/4 bg-muted animate-pulse rounded" />
</div>
)
// ❌ "No data" — useless
{data.length === 0 && <p>No data</p>}
// ✅ Contextual and actionable
{data.length === 0 && (
<div className="text-center py-12">
<Trophy className="mx-auto text-muted mb-4" size={48} />
<h3 className="text-lg font-medium mb-2">No challenges yet</h3>
<p className="text-muted mb-4">Enter your first challenge to start climbing the ranks.</p>
<Button asChild><Link href="/challenges">Browse Challenges</Link></Button>
</div>
)}