React's flexibility is both its greatest strength and its most common pitfall. A small application can get by with minimal structure, but as codebases grow beyond 50-100 components, the lack of enforced conventions leads to inconsistency, performance degradation, and developer frustration. These practices have emerged from scaling React applications with hundreds of components and millions of users.
Project Structure and Module Boundaries
Organize code by feature, not by file type. A feature folder contains its components, hooks, utilities, and tests, everything needed to understand and modify that feature in isolation. Shared code lives in a separate module with explicit exports. This structure makes it easy to find related code and prevents cross-feature coupling.
State Management at Scale
Not all state is equal. Local component state (useState), shared UI state (Context or Zustand), server-cache state (React Query/TanStack Query), and URL state (search params) each have different lifecycles and access patterns. Using the right tool for each type prevents the complexity explosion that comes from putting everything in a global store.
| State Type | Best Tool | When to Use |
|---|---|---|
| Local component | useState / useReducer | Form inputs, toggles, component-only data |
| Shared UI | Context or Zustand | Theme, sidebar open, modal visibility |
| Server cache | React Query / TanStack Query | Data fetched from APIs |
| URL / routing | useSearchParams | Filters, pagination, shareable state |
| Form state | React Hook Form | Complex forms with validation |
- Keep component state local whenever possible
- Use React Query for server state since it handles caching, refetching, and synchronization
- Reserve global stores for truly global UI state (theme, sidebar, modals)
- Derive state from props and URL params instead of duplicating it
- Avoid prop drilling beyond 2-3 levels. Use composition or context instead
Performance Optimization
React's reconciliation algorithm is fast, but unnecessary re-renders accumulate. Profile before optimizing. React DevTools Profiler identifies the actual bottlenecks. Common wins include memoizing expensive computations (useMemo), stabilizing callback references (useCallback), code-splitting routes and heavy components (lazy/Suspense), and virtualizing long lists.
The biggest performance improvement in most React applications is not memoization. It is reducing the amount of state that triggers re-renders in the first place. Structure your component tree so that state lives close to where it is consumed.
Testing Strategy
Test behavior, not implementation. Use React Testing Library to test components from the user's perspective: what they see and what they can interact with. Reserve unit tests for complex business logic. Use end-to-end tests (Playwright, Cypress) for critical user flows. The testing pyramid applies: many unit tests, fewer integration tests, and a handful of E2E tests covering the most important paths.
Code Review Standards
Establish and enforce code review standards that cover component composition, hook usage, accessibility, and performance patterns. Automated linting (ESLint) catches formatting and basic issues. Code reviews catch architectural and design decisions. Both are necessary for maintaining consistency in large teams.