React Patterns

Component Design

• Single responsibility: one component, one concern
• Composition over props: compound components pattern instead of boolean props
• Presentational vs container: separate rendering from logic
• Small components: if it's >100 lines, extract

Hooks Rules

• Only call hooks at the top level (not in conditions, loops, callbacks)
• Only call hooks from React functions
• useEffect dependencies must be exhaustive (use the linter rule)
• Custom hooks start with use and compose primitive hooks

Performance

• React.memo for pure components that re-render often with same props
• useMemo/useCallback for expensive computations (measure first!)
• Virtualize long lists (react-window, react-virtuoso)
• Lazy load routes and heavy components (React.lazy, Suspense)
• Avoid passing new objects/arrays as props (use useMemo or stable references)

State Management

• Local state first: useState > useReducer > context > external library
• Context for shared global state (theme, auth, locale)
• Zustand/Redux only when state logic is truly complex or shared across many components
• Colocate state with the component that needs it