React Code Review Patterns
Checklists and patterns for reviewing React/TypeScript frontend code.
Quick Reference
| Priority | Category | Key Checks |
|----------|----------|------------|
| 1 | Security | No secrets, XSS prevention, safe innerHTML |
| 2 | Type Safety | No any, explicit types, proper generics |
| 3 | React Patterns | Hooks rules, component structure, keys |
| 4 | Performance | Memoization, bundle size, re-renders |
| 5 | Accessibility | ARIA, keyboard nav, semantic HTML |
TypeScript Checklist
| Check | Required Pattern | Anti-Pattern |
|-------|------------------|--------------|
| Type annotations | Explicit types | any, implicit any |
| Generics | Proper constraints | <any> |
| Null handling | Strict null checks | ! assertions |
| Type guards | Proper narrowing | Type casting |
| API types | Generated from schema | Manual types |
| Enums | String enums or const objects | Numeric enums |
React Components Checklist
| Check | Required Pattern | Anti-Pattern |
|-------|------------------|--------------|
| Component type | Functional components | Class components |
| Props typing | Interface/type for props | Inline types, any |
| Default props | Default parameters | defaultProps |
| Children | Explicit children prop | Implicit |
| Fragments | <> or Fragment | Unnecessary divs |
| Keys | Stable, unique keys | Index as key |
Hooks Checklist
| Check | Required Pattern | Anti-Pattern |
|-------|------------------|--------------|
| Hook rules | Top level only | Conditional hooks |
| Dependencies | Complete deps array | Missing deps, // eslint-disable |
| useEffect cleanup | Return cleanup function | Missing cleanup |
| Custom hooks | use prefix | Non-hook abstractions |
| useMemo/useCallback | For expensive ops | Premature optimization |
State Management Checklist
| Check | Required Pattern | Anti-Pattern |
|-------|------------------|--------------|
| Server state | React Query | useState for API data |
| Client state | Context or useState | Redux for simple state |
| Form state | React Hook Form | Manual form handling |
| Loading states | isLoading, isError | Boolean flags |
| Optimistic updates | React Query mutations | Manual state sync |
API Integration Checklist
| Check | Required Pattern | Anti-Pattern |
|-------|------------------|--------------|
| Data fetching | useQuery | useEffect + fetch |
| Mutations | useMutation | Direct API calls |
| Error handling | Error boundaries + query errors | Try-catch everywhere |
| Caching | React Query cache | Manual caching |
Performance Checklist
| Check | Required Pattern | Anti-Pattern |
|-------|------------------|--------------|
| Re-renders | Memoized callbacks | Inline functions in JSX |
| Lists | Virtualization for long lists | Render all items |
| Lazy loading | React.lazy + Suspense | All code in bundle |
| Images | Lazy loading, proper sizes | Unoptimized images |
Accessibility Checklist
| Check | Required Pattern | Anti-Pattern |
|-------|------------------|--------------|
| Semantic HTML | <button>, <nav>, <main> | <div onClick> |
| ARIA labels | aria-label, aria-describedby | Missing labels |
| Keyboard nav | tabIndex, focus management | Mouse-only interactions |
| Color contrast | WCAG AA compliant | Low contrast |
| Form labels | <label htmlFor> | Placeholder only |
Testing Checklist
| Check | Required Pattern | Anti-Pattern |
|-------|------------------|--------------|
| Test coverage | Tests for components | No tests |
| Test type | Behavior tests | Implementation tests |
| Queries | getByRole, getByLabelText | getByTestId |
| Async | waitFor, findBy | Manual timeouts |
| Mocking | MSW for API | Mock fetch directly |
General Checklist
| Check | Required Pattern | Anti-Pattern |
|-------|------------------|--------------|
| Console | No console.log | Debug statements |
| Comments | Explain "why" | Explain "what" |
| File size | <300 lines per component | Monolithic components |
| Imports | Absolute paths | Relative hell ../../../ |
Common Anti-Patterns
| Anti-Pattern | Issue | Correct Pattern |
|--------------|-------|-----------------|
| any type | Loses type safety | Explicit types |
| Index as key | Causes re-render bugs | Stable unique ID |
| Inline functions | Re-creates on render | useCallback |
| useEffect for derived state | Unnecessary effect | Compute in render |
| // eslint-disable | Hiding real issues | Fix the issue |
| Direct DOM manipulation | Bypasses React | Refs or state |
| dangerouslySetInnerHTML | XSS risk | Sanitize or avoid |
| Missing error boundaries | Crashes whole app | Error boundary wrapper |
References
- references/examples.md - Code examples for patterns