Top 10 React Developer Interview Questions & Answers in 2024

1. How does React handle state and props, and what are the key differences between them?

React components use state to manage internal data that can change over time, while props are used to pass data from a parent component to its child components. State is mutable and can be changed using setState(), while props are immutable. Understanding these concepts is crucial for managing data flow within a React application.

2. Explain the concept of React reconciliation and when it occurs during the rendering process.

React reconciliation is the process of comparing the virtual DOM with the previous virtual DOM to determine the minimum number of DOM manipulations required to update the UI. It occurs during the rendering phase, specifically in the render() method or when setState() is called. Reconciliation is essential for optimizing performance by minimizing unnecessary updates to the actual DOM.

3. How can you optimize the rendering performance of a React application, and what tools can assist in identifying performance bottlenecks?

Optimizing rendering performance involves techniques like memoization, using PureComponent or React.memo for preventing unnecessary re-renders, and implementing code splitting to load only essential components. Tools like React DevTools, Chrome Developer Tools, and performance monitoring libraries like React Profiler assist in identifying and addressing performance bottlenecks.

4. Discuss the advantages and disadvantages of using CSS-in-JS solutions like Styled Components in React development.

CSS-in-JS solutions like Styled Components offer advantages such as scoped styling, dynamic theming, and improved component encapsulation. However, they may introduce a learning curve, increase bundle size, and impact the separation of concerns. Assessing project requirements, team familiarity, and potential trade-offs is crucial when deciding whether to use a CSS-in-JS solution.

5. How does React Router handle dynamic routing, and what are the benefits of using dynamic routes in a React application?

React Router supports dynamic routing by allowing parameters in route paths, which are then accessible in the component via the useParams hook or match.params in class components. Dynamic routes enable the creation of reusable components, reducing redundancy in code. They also provide a more flexible and scalable way to handle various user inputs and scenarios within a React application.

6. Explain the significance of React Hooks and provide examples of when to use useEffect and useContext in functional components.

React Hooks are functions that enable the use of state and lifecycle features in functional components. useEffect is used for handling side effects, such as data fetching or subscriptions. useContext allows accessing context values within a component. For example, useEffect might be used to fetch data after component mount, and useContext for accessing global application state.

7. How can you manage state across multiple components in a React application, and what role does lifting state up play in this process?

Lifting state up involves moving the state from child components to a common parent component. This helps in managing shared state across multiple components. By passing down state and callbacks as props, child components can update the shared state. This pattern promotes a single source of truth and simplifies state management in complex React applications.

8. Discuss the purpose of React portals and provide an example of when you might use them in a React application.

React portals provide a way to render children components outside their parent DOM hierarchy, often useful for implementing modal dialogs, tooltips, or overlays. For example, when creating a modal that should appear on top of the entire application but needs to be managed independently, a portal can be used to render it outside the main container.

9. How can you implement server-side rendering (SSR) in a React application, and what are the benefits of using SSR?

Server-side rendering involves rendering React components on the server before sending them to the client. This can be achieved using frameworks like Next.js. SSR improves initial page load times, enhances SEO by providing search engines with fully rendered HTML content, and ensures a more efficient user experience, especially on slower network connections.

10. Discuss the concept of code splitting in React and how it contributes to better application performance.

Code splitting involves breaking down a React application into smaller chunks or bundles that are loaded on-demand. This technique reduces the initial load time and improves performance by only loading the necessary code for the current user flow. React.lazy and dynamic imports are common tools for implementing code splitting, allowing developers to optimize the bundle size and prioritize critical components.