React design interview question with expected answers

How would you design a scalable and reusable component architecture for a complex web application?

Scenario:

You’re tasked with building a dashboard for a large enterprise application. The dashboard includes charts, tables, filters, and widgets. It should support dynamic data updates, user customizations, and internationalization.

Key Points the Interviewer is Looking For:

• Understanding of modularity and reusability.
• Handling state management effectively.
• Use of context or external state libraries.
• Proper organization of the project directory.
• Adherence to best practices (e.g., separation of concerns, avoiding prop drilling).

Expected Solution

1. Component Hierarchy and Modularity

Break the UI into smaller, reusable components:

• Atomic Design Principle:
  • Atoms: Smallest components (e.g., Button, Input, Label).
  • Molecules: Group of atoms working together (e.g., SearchBar with Input and Button).
  • Organisms: Complex components (e.g., Table with Pagination and Filters).
  • Templates: Layouts using organisms (e.g., Dashboard layout).
  • Pages: Complete views (e.g., HomePage, DashboardPage).

2. State Management

• Use local state for component-specific logic: const [selectedFilter, setSelectedFilter] = useState(null);
• Use Context API for cross-cutting concerns like theme, language, and user preferences.
• Use Redux or Zustand for global application state to handle:
  • Dynamic data updates (e.g., API calls for charts).
  • User customizations (e.g., saving user settings).
  • Shared state between unrelated components.

3. Component Composition

Leverage composition over inheritance to create flexible components:

function Card({ children, title }) {
  return (
    <div className="card">
      <h3>{title}</h3>
      <div>{children}</div>
    </div>
  );
}

Usage:

<Card title="Sales Data">
  <Chart data={salesData} />
</Card>

4. Styling Strategy

• Use CSS-in-JS libraries like styled-components or Emotion for dynamic styles.
• Follow a BEM naming convention if using traditional CSS.
• Modularize styles to keep them scoped: import styles from './Chart.module.css';

5. Internationalization (i18n)

• Use libraries like react-intl or i18next for multilingual support: <FormattedMessage id="dashboard.title" defaultMessage="Dashboard" />

6. Directory Structure

Organize the project for scalability:

src/
  components/
    atoms/
    molecules/
    organisms/
  pages/
    Dashboard/
    Home/
  context/
    ThemeContext.js
    LanguageContext.js
  hooks/
    useFetch.js
  utils/
    formatDate.js
  redux/
    slices/
    store.js
  styles/
    global.css

7. Data Fetching and Updates

• Use React Query (@tanstack/react-query) for data fetching, caching, and updates: const { data, isLoading } = useQuery('fetchChartData', fetchChartData);

8. Error Boundaries

• Handle component-level errors gracefully with an error boundary: class ErrorBoundary extends React.Component { state = { hasError: false }; static getDerivedStateFromError() { return { hasError: true }; } render() { if (this.state.hasError) { return <h1>Something went wrong.</h1>; } return this.props.children; } }

9. Testing

• Write unit tests for components using Jest and React Testing Library.
• Test complex interactions (e.g., filters affecting charts). test('renders dashboard with charts and filters', () => { render(<Dashboard />); expect(screen.getByText('Dashboard')).toBeInTheDocument(); });