React State Management

React State Management

Priority: P0 (CRITICAL)

Choosing the right tool for state scope.

Implementation Guidelines

• Local: useState. useReducer if complex (state machine).
• Derived: const fullName = first + last. No state sync.
• Context: DI, Theming, Auth. Not for high-freq data.
• Global: Zustand/Redux for app-wide complex flow.
• Server Cache: Use React.cache (RSC) to dedupe requests per render.
• Server State: React Query / SWR / Apollo. Cache != UI State.
• URL: Store filter/sort params in URL (Source of Truth).
• Immutability: Never mutate. Use spread or Immer.

Anti-Patterns

• No Prop Drilling > 2: Use Context/Composition.
• No Mirroring Refs: Don't copy props to state.
• No Multi-Source: Single Source of Truth.
• No Context Abuse: Context causes full-tree re-render.

Code

// Derived State (Efficient)
function List({ items, filter }) {
  // Correct: Calculated on fly
  const visible = items.filter((i) => i.includes(filter));
  return (
    <ul>
      {visible.map((i) => (
        <li key={i}>{i}</li>
      ))}
    </ul>
  );
}

// Zustand (Global)
const useStore = create((set) => ({
  count: 0,
  inc: () => set((s) => ({ count: s.count + 1 })),
}));

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