Expert Answers To Common ReactJS Interview Questions At Lloyds Banking Group

1. React Fundamentals and Hooks

Question: Can you explain the difference between class components and functional components in React? When would you use each?

Answer:
In React, class components are ES6 classes that extend React.Component. They manage their own state and have access to lifecycle methods such as componentDidMount, componentDidUpdate, and componentWillUnmount. Functional components are simpler and are defined as JavaScript functions that return JSX. They don’t manage state or have lifecycle methods by default, but can do so using React Hooks like useState and useEffect.

Usage:

• Use class components when you need to manage state or use lifecycle methods.
• Use functional components for simpler components that don’t require state or lifecycle methods, or when you want to utilize Hooks for state management and side effects.

2. Micro-frontend Architecture Principles

Question: What are the key principles of micro-frontend architecture? How does it differ from monolithic architecture?

Answer:
Micro-frontend architecture decomposes a frontend monolith into smaller, independently deployable applications that can be developed, tested, and deployed separately. Key principles include:

• Independence: Each micro-frontend can be developed and deployed independently.
• Integration: Modules communicate and integrate seamlessly using standards like Webpack Module Federation or custom APIs.
• Scalability: Enables scaling of development teams and improves overall agility.
• Isolation: Ensures that failures in one micro-frontend do not affect others.

Difference from Monolithic:

• Monolithic architectures are single, cohesive units where all frontend components are tightly coupled and deployed together.
• Micro-frontend architectures allow for greater flexibility, scalability, and independent development lifecycles.

3. Module Federation and State Sharing

Question: How does Module Federation in Webpack facilitate micro-frontend development? Can you explain how you would share state between micro-frontends?

Answer:
Module Federation allows separate webpack builds to work together at runtime. It enables sharing of modules (including React components) across different applications without the need for separate deployments. State sharing between micro-frontends can be achieved through:

• Global State Management: Using a centralized state store (e.g., Redux or Recoil) that all micro-frontends can access.
• Event-Driven Communication: Using events or messages (e.g., through a message broker or custom event system) to communicate state changes.
• API Integration: Using APIs to fetch and update shared state.

4. Accessibility (a11y) Best Practices

Question: What are some key accessibility considerations when developing a web application? How would you ensure your React components are accessible?

Answer:
Key considerations include:

• Semantic HTML: Use appropriate HTML elements (<button>, <input>, etc.) and semantic markup (<nav>, <header>) to provide context to screen readers.
• Keyboard Accessibility: Ensure all interactive elements are operable via keyboard navigation.
• ARIA Roles and Attributes: Use ARIA roles and attributes to enhance accessibility for complex widgets and dynamic content.
• Color Contrast: Ensure sufficient color contrast between text and background elements.
• Testing: Regularly test accessibility using tools like Axe or Lighthouse, and conduct manual testing with screen readers.

Ensuring Accessibility in React:

• Use accessible HTML elements (<button> instead of <div> for buttons).
• Implement keyboard navigation and focus management within components.
• Use ARIA attributes (role, aria-label, aria-describedby) where appropriate.
• Test components with accessibility tools and address any issues found.

5. Performance Optimization and Sustainability

Question: How would you optimize the performance of a React application? What are some strategies for ensuring sustainable development practices?

Answer:
Performance Optimization:

• Code Splitting: Splitting bundles to load only necessary code for initial render and lazy loading components.
• Bundle Size: Minimize bundle size by using tree shaking, optimizing imports, and reducing dependencies.
• Network Efficiency: Use CDN for static assets, implement HTTP/2, and cache API responses.
• Performance Monitoring: Use tools like Chrome DevTools, Lighthouse, or Web Vitals for monitoring and optimizing performance metrics.

Sustainability:

• Optimized Code: Write efficient code to reduce energy consumption and carbon footprint.
• Green Hosting: Choose eco-friendly hosting providers and data centers.
• Continuous Optimization: Regularly revisit and optimize code and infrastructure for sustainability.
• Educate Teams: Promote awareness and best practices for sustainable development among team members.

6. State Management (Redux, MobX, Recoil)

Question: Compare Redux, MobX, and Recoil as state management solutions in React. When would you choose one over the others?

Answer:

• Redux: Centralized state management with a single store and predictable state mutations using actions and reducers. Suitable for large-scale applications with complex state management needs and time-travel debugging.
• MobX: Uses observables to manage state and automatically tracks dependencies between state and components. Suitable for applications with complex reactive state requirements and minimal boilerplate.
• Recoil: State management library specifically designed for managing global and local state in React components. It provides primitives for managing and sharing state atomically.

Choosing Between Them:

• Choose Redux for applications needing strict state management and debugging capabilities.
• Choose MobX for applications where reactivity and minimal boilerplate are important.
• Choose Recoil for applications needing simple, efficient state management directly tied to React components.

7. JavaScript/TypeScript Proficiency

Question: What are some advantages of using TypeScript with React? How would you convert a JavaScript project to TypeScript?

Answer:
Advantages:

• Static Typing: Catching errors during development and improving code quality.
• Tooling Support: Better IDE support, autocompletion, and refactoring capabilities.
• Code Readability: Improved readability with type annotations.

Converting to TypeScript:

• Setup: Install TypeScript and configure tsconfig.json with desired settings.
• Conversion Steps: Start by renaming .js files to .ts or .tsx, fix any type errors, and gradually add type annotations to variables, functions, and components.
• Testing: Use TypeScript compiler (tsc) and IDE support to fix any type errors throughout the project.

8. CSS-in-JS and Responsive Design

Question: How does CSS-in-JS improve component styling in React? Describe how you would implement responsive design in a React application.

Answer:
CSS-in-JS:

• Scoped Styles: Encapsulation of styles to avoid global namespace conflicts.
• Dynamic Styling: Conditionally applying styles based on component props or state.
• Performance: Optimizing rendering by eliminating unused styles.

Responsive Design:

• Media Queries: Use CSS @media queries to apply different styles based on viewport size.
• Flexbox/Grid: Utilize Flexbox or CSS Grid for responsive layouts and component positioning.
• Responsive Components: Use React components that adapt their layout and behavior based on screen size.

9. Testing (Including Accessibility Testing)

Question: What testing strategies would you employ to ensure the quality and accessibility of a React application? How would you integrate testing into a CI/CD pipeline?

Answer:
Testing Strategies:

• Unit Tests: Using Jest for testing individual components and functions.
• Integration Tests: Testing how components work together and with external services.
• End-to-End Tests: Using tools like Cypress for simulating user interactions and testing complete workflows.
• Accessibility Tests: Conducting manual and automated tests using Axe or Lighthouse to ensure compliance with accessibility standards.

CI/CD Integration:

• Automation: Configure CI/CD pipelines (e.g., Jenkins, GitLab CI) to run tests automatically on every code change.
• Quality Gates: Set up checks to ensure tests pass before deploying changes to production.
• Accessibility Checks: Integrate accessibility tests into the pipeline using tools like Axe or Lighthouse.

10. CI/CD and Green Deployment Strategies

Question: Describe the benefits of CI/CD for web development. How would you implement green deployment strategies to minimize downtime and risk?

Answer:
Benefits of CI/CD:

• Automation: Automating build, test, and deployment processes to increase efficiency and consistency.
• Faster Time to Market: Rapidly deploying changes and features to production.
• Reduced Risk: Catching errors early through automated testing and validation.

Green Deployment Strategies:

• Blue-Green Deployment: Deploying new versions to separate environments (blue and green) and switching traffic after validation.
• Canary Releases: Rolling out changes gradually to a subset of users to monitor performance and catch issues early.
• Feature Toggles: Using feature flags to enable or disable new features without deploying code changes.