state-management

Frontend State Management

Overview

Patterns and best practices for managing state in frontend applications across different frameworks.

State Categories

Local vs Global State

Type	Scope	Examples	Solution
Local UI	Single component	Form inputs, modals, dropdowns	useState, ref
Shared UI	Component subtree	Theme, sidebar state	Context, provide/inject
Server	Cached API data	Users, products, orders	TanStack Query, SWR
Global App	Entire app	Auth, settings, notifications	Zustand, Pinia, Redux
URL	Browser URL	Filters, pagination, search	Router params/query

When to Use What

┌─────────────────────────────────────────────────────────┐
│ Does only this component need it?                       │
│   YES → Local state (useState/ref)                      │
│   NO ↓                                                  │
├─────────────────────────────────────────────────────────┤
│ Is it server data that needs caching/sync?              │
│   YES → Server state library (TanStack Query)           │
│   NO ↓                                                  │
├─────────────────────────────────────────────────────────┤
│ Is it in the URL (shareable state)?                     │
│   YES → URL state (router)                              │
│   NO ↓                                                  │
├─────────────────────────────────────────────────────────┤
│ Is it needed across unrelated components?               │
│   YES → Global store (Zustand/Pinia)                    │
│   NO → Lift state up or Context                         │
└─────────────────────────────────────────────────────────┘

Server State (TanStack Query)

Basic Query Pattern

// Define query
function useUsers(filters: UserFilters) {
  return useQuery({
    queryKey: ['users', filters],
    queryFn: () => api.getUsers(filters),
    staleTime: 5 * 60 * 1000, // 5 minutes
    gcTime: 30 * 60 * 1000,   // 30 minutes
  });
}

// Use in component
function UserList() {
  const [filters, setFilters] = useState<UserFilters>({});
  const { data, isLoading, error } = useUsers(filters);

  if (isLoading) return <Spinner />;
  if (error) return <Error message={error.message} />;
  return <List items={data} />;
}