React Expert
Core Philosophy
Components consume external state, contain no logic:
- External hooks at top (Zustand, XState, TanStack Query)
- No useState/useReducer/useEffect for complex logic
- Inline actions unless repeated 2+ times
- Test stores/machines (unit tests), not components (E2E only)
State Management Stack
| State Type |
Solution |
| Remote (REST) |
TanStack Query |
| Remote (GraphQL) |
Apollo Client |
| Application state |
Zustand |
| Complex machines |
XState |
| Local UI state |
useState (rare, last resort) |
Component Pattern
// ✅ External hooks → Early returns → JSX
function UserProfile({ userId }: { userId: string }) {
const { user, isLoading } = useUser(userId);
const { updateProfile } = useUserActions();
if (isLoading) return <Spinner />;
return (
<div>
<h1>{user.name}</h1>
<button => updateProfile({ email: 'new@example.com' })}>
Update
</button>
</div>
);
}
Testing: Stores, Not Components
| What |
Tool |
Why |
| Zustand stores |
Vitest |
Test without React |
| XState machines |
Vitest |
Deterministic transitions |
| Critical flows |
Playwright |
Real browser |
| Components |
Never |
Logic should be in stores |
// Test store directly
const { login } = useAuthStore.getState();
await login({ email: "test@example.com", password: "pass" });
expect(useAuthStore.getState().user).toBeDefined();
Unique Patterns
Prop Ordering: Simple → Complex
<Table
data={items}
loading={isLoading}
sortable
renderRow={(item) => <Row>{item.name}</Row>}
/>
Inline Props for Type Inference
// ✅ Inline - TypeScript infers types
<SearchableList
items={budgets}
renderItem={(budget) => <Card name={budget.name} />}
/>;
// ❌ Extract only if repeated 2+ times
const renderItem = (budget: Budget) => <Card name={budget.name} />;
Pattern Matching for Variants
import { match } from "ts-pattern";
{
match(state)
.with({ _tag: "loading" }, () => <Spinner />)
.with({ _tag: "success" }, (s) => <Data value={s.data} />)
.exhaustive();
}
Performance: Profile First
| Technique |
When |
| useMemo |
Profiled as slow |
| useCallback |
Repeated 2+ times |
| React.memo |
Props rarely change |
| Code splitting |
Route-level |
Styled-Components: Consolidate with CSS Selectors
// ✅ Single component with CSS selectors
const Table = styled.table`
thead {
background: ${(p) => p.theme.colors.header};
}
tbody tr:hover {
background: ${(p) => p.theme.colors.hover};
}
td {
padding: ${(p) => p.theme.space.md};
}
`;
// ❌ Separate components for each element
const TableHeader = styled.thead`...`;
const TableRow = styled.tr`...`;
const TableCell = styled.td`...`;
Version 1.0.1
majiayu000