React Frontend

REACT FRONTEND — Production Standards 2025

Component Architecture

Single Responsibility (non-negotiable)

// ❌ God component
function Dashboard() { /* auth + fetch + render + modal = untestable */ }

// ✅ Composed
function Dashboard() {
  return <DashboardLayout><JobList /><MetricsPanel /></DashboardLayout>
}

Props — Always typed, minimal surface

interface ButtonProps {
  label: string
  onClick: () => void
  variant?: 'primary' | 'danger' | 'ghost'
  disabled?: boolean
  isLoading?: boolean
}
// No "any", no prop drilling > 2 levels → use context or state manager

State Management Decision Tree

• Local UI state → useState (open/close, form fields)
• Async server state → TanStack Query (fetch, cache, refetch)
• Global shared state → Zustand (auth, theme, cart)
• URL state → useSearchParams (filters, pagination)
• NEVER → Redux for new projects in 2025

Hooks Patterns

Data fetching (TanStack Query)

function JobList() {
  const { data, isLoading, error } = useQuery({
    queryKey: ['jobs', filters],
    queryFn: () => fetchJobs(filters),
    staleTime: 30_000,
  })
  if (isLoading) return <Skeleton />
  if (error) return <ErrorBoundary error={error} />
  return <ul>{data.map(job => <JobCard key={job.id} {...job} />)}</ul>
}

Custom hook — encapsulate logic, not JSX

function useJobSubmit() {
  const mutation = useMutation({
    mutationFn: submitJob,
    onSuccess: () => queryClient.invalidateQueries({ queryKey: ['jobs'] }),
  })
  return { submit: mutation.mutate, isPending: mutation.isPending }
}

Performance Rules

• React.memo() only after profiling — not by default
• useCallback / useMemo only for expensive operations or stable refs
• Dynamic imports for routes: const Page = lazy(() => import('./Page'))
• Images: always width + height attributes (prevent CLS)
• Lists: always key prop that is a stable unique ID (never array index)

Accessibility (MANDATORY)

// Buttons must have text or aria-label
<button aria-label="Close dialog" /></button>

// Forms must have associated labels
<label htmlFor="email">Email</label>
<input id="email" type="email" required />

// Color contrast: 4.5:1 minimum for normal text

Forbidden Patterns

❌ useEffect for data fetching (use TanStack Query) ❌ index as key in dynamic lists ❌ Inline styles for anything beyond one-off overrides ❌ any type in TypeScript ❌ Nested ternaries in JSX (extract to variable or component) ❌ React SPA for content sites (use Next.js/Astro instead)