Keeping up with the current trends and interview questions is essential for both hiring managers and job seekers, as React JS maintains its dominance in the web development industry. Whether you’re a recruiter trying to identify the top talent or an experienced React developer searching for a career change, this thorough list of Top 40+ React JS interview questions and answers for 2024 will help you properly prepare and assess prospects.
React js interview questions & answers
1. What is React JS, and why is it popular in 2024?
An open-source JavaScript package called React JS is used to create user interfaces. It is renowned for being quick and effective, allowing programmers to design dynamic and extremely responsive online applications. React is still very popular in 2024 because of its component-based architecture, robust community, and capacity to create scalable and dynamic web applications.
2. What are React Components, and how are they created?
React Components are the building blocks of a React application. They are reusable, self-contained pieces of code that define a part of a user interface. Components can be created in two ways: functional components using ES6 functions or class components that extend the React. Component class.
3. What is the Virtual DOM in React, and why is it important?
An in-memory copy of the real DOM is called the Virtual DOM. It is used by React to streamline the update procedure. React minimizes the number of actual DOM manipulations by updating the Virtual DOM first and then comparing it with the real DOM when a component is modified. As a result, the user experience is enhanced and performance is enhanced.
4. Explain JSX in React.
JSX, or JavaScript XML, is an extension of JavaScript that allows you to write HTML-like code within JavaScript. It’s used in React to describe what the UI should look like. JSX is transpiled into regular JavaScript by tools like Babel. For example, <div>Hello, React!</div> in JSX gets transformed into React.createElement('div', null, 'Hello, React!').
5. What is the difference between state and props in React?
In React, props and state are both used to pass data, but for different reasons. Props are used to transfer data from a parent component to a child component, while the state is used to handle data that can change within a component. Props are read-only and under the parent component’s control, but the state is changeable and controlled by the component itself.
6. What is a higher-order component (HOC) in React?
In React, a higher-order component is a pattern where a component is wrapped around another component to share functionality. Tasks like logic sharing, code reuse, and state management abstraction are performed by HOCs. They improve React components’ maintainability and reusability.
7. What are hooks in React, and how do they differ from class components?
In version 16.8, React introduced hooks, which made it possible for functional components to use state and other React features. They offer an easier-to-use API for React concepts that were previously limited to class components. Stateful logic can be more easily reused and classes are not necessary thanks to hooks like ‘useState’ and ‘useEffect’.
8. What is the significance of the useEffect hook in React?
The useEffect hook is used for side effects in functional components. It allows you to perform tasks such as data fetching, DOM manipulation, or setting up subscriptions. useEffect runs after the render is committed to the screen and helps in keeping the component’s behavior in sync with the application state.
9. How can you optimize the performance of a React application?
React performance optimization can be accomplished through code splitting, memoization, lazy loading, and virtual DOM update optimization. Performance bottlenecks can also be found and removed by profiling components with tools like React DevTools and avoiding pointless re-renders.
10. What is server-side rendering (SSR) in React, and why is it important?
React applications that are rendered initially on the server instead of in the browser are known as server-side rendering applications. By supplying the client with a fully rendered page, SSR eliminates the need for client-side rendering and enhances SEO, page load speeds, and user experience.
11. What is the Context API in React, and how does it differ from props?
Without specifically passing data through props, a tree of React components can share data that can be deemed global thanks to the Context API. It’s especially helpful for transmitting data that needs to be accessed by several components, such as theme information or user authentication data. The Context API enables any component in the tree to access data without requiring it to be passed explicitly, in contrast to props, which pass data from parent to child components.
12. Explain the concept of React Router and its use in single-page applications.
One well-liked library for managing routing in single-page applications (SPAs) is React Router. It enables programmers to specify various application routes and display various components according to the URL. In an SPA, React Router offers a smooth method of page navigation that eliminates the need for complete page reloads. Creating intricate and multi-page-like user experiences on a single web page requires it.
13. What are portals in React, and when would you use them?
React portals let you render children of a component into an external DOM element that isn’t part of the parent component’s DOM hierarchy. They come in handy when you have to render elements such as dropdown menus, modals, or tooltips outside of the standard document flow. This is usually done to prevent conflicts with parent components’ styling and positioning.
14. What is Redux, and how does it work with React?
Redux is a JavaScript state management library that is frequently used in conjunction with React. It offers a centralized, predictable state management system that simplifies the handling of intricate interactions and application data management. Redux uses reducers and actions to let components access and change the application’s state, which is stored in a single immutable object. Large and complicated applications where effective management of shared state is required will find it especially helpful.
15. What are React Hooks like useCallback and useMemo, and why are they important for performance optimization?
React provides hooks like useCallback and useMemo to optimize performance. useCallback is used to memoize functions, ensuring that a function reference remains the same between renders unless its dependencies change. This can prevent unnecessary re-renders of child components. useMemo is used to memoize the result of a function, allowing for efficient computation of values based on dependencies. Both hooks are essential for improving the performance of React components.
16. How does server-side rendering (SSR) work in React, and what are the benefits and challenges associated with it?
In React, server-side rendering is rendering the first HTML on the server instead of sending it to the client’s browser. Improved user experience, quicker first page load times, and better SEO are among the advantages. Difficulties may include more intricate server configuration, higher server load, and possibly slower client-side navigation after the first page loads.
17. Explain the concept of lazy loading in React and how it helps in code splitting.
Using the lazy loading technique, you can load assets or components asynchronously and only when needed. Because components load on demand, this can drastically lower the initial bundle size of a React application. Lazy loading helps with code splitting, which reduces the amount of JavaScript that needs to be loaded upfront and speeds up initial page loads.
18. How do you handle authentication and authorization in a React application?
In a React application, handling authorization and authentication frequently entails utilizing methods like OAuth, token-based authentication, or integration with authentication providers. Authorization checks are carried out to ascertain what actions or routes a user is permitted to access after they have been authenticated. Based on the user’s authentication and authorization status, routes can be managed and protected using libraries like React Router and state management tools like Redux.
19. Explain the concept of code splitting in React and how it improves application performance.
The process of dividing a JavaScript bundle into smaller, easier-to-manage parts is known as “code splitting.” As users navigate through the application, these pieces load as needed, which speeds up the initial load time and enhances performance. For larger applications, code splitting is especially crucial to ensuring quicker first page loads and a more responsive user experience.
20. What are the key differences between controlled and uncontrolled components in React forms?
React controls the values of controlled components in React forms, and they are dependent on the state of the component. Any changes made by the user update the state, and the component re-renders to show the updated information. DOM control over the value of the input field is granted by uncontrolled components. Usually, you use them to integrate React with non-React code or libraries or to avoid having to deal with input values inside the state of the component.
21. What is the significance of the key prop in React and when should you use it?
The key prop is used to help React identify individual elements within an array. It is essential when rendering dynamic lists of components, such as in a map function. Using a unique key for each element helps React efficiently update and re-render the list when changes occur, preventing unexpected behavior or performance issues.
22. What is server-side rendering (SSR) in React, and how does it differ from client-side rendering (CSR)?
The process of rendering a React application on the server and delivering the fully rendered HTML to the client is known as server-side rendering or SSR. Because the HTML content is instantly available with SSR, there are benefits to SEO and better initial page load performance. Client-side rendering (CSR), on the other hand, loads a minimal HTML shell and uses JavaScript to render the page. This may cause the page to load more slowly at first and pose possible SEO issues.
23. Explain the concept of code splitting in React and how it is implemented.
Code splitting in React involves breaking the application’s JavaScript bundle into smaller, more manageable chunks that can be loaded on demand. This technique is achieved using dynamic imports or tools like Webpack’s dynamic imports. Code splitting reduces the initial bundle size, improving page load times and overall application performance by loading only the necessary code as users navigate through the app.
24. What is the purpose of React Fiber, and how does it impact the performance of React applications?
React Fibre is a re-implementation of the core React algorithm aimed at enhancing React applications’ responsiveness and performance. It brings in a more effective method of component reconciliation and rendering, enabling more precise control over rendering priorities. React Fibre makes it easier to create fluid, high-performing applications and reduces jank, which improves the user experience.
25. What are React Portals, and how are they useful in creating modal dialogs or tooltips?
You can render components outside of the DOM hierarchy of their parent component with React Portals. Their special utility lies in their ability to create components that require rendering in a different area of the DOM, such as tooltips or modal dialogues. The modal or tooltip is not restricted by the boundaries of the parent component thanks to React Portals, which also avoid styling and positioning conflicts.
26. What are the potential performance bottlenecks in a React application, and how can you address them?
React applications may experience performance bottlenecks due to inefficient rendering, an excessive number of renders, or a large component count. Developers can use methods like memoization (with useMemo and useCallback), PureComponent, and React. memo, and shouldComponentUpdate to stop pointless re-renders to solve these problems. Performance issues can also be resolved by code splitting, lazy loading, and API request optimization.
27. What is the significance of React Suspense and Concurrent Mode, and how do they enhance the user experience?
Features like Concurrent Mode and React Suspense are there to make using React applications more enjoyable for users. Suspense removes the need to load spinners or placeholders by allowing components to pause rendering until data is ready. Conversely, Concurrent Mode makes it possible for React to work on several tasks at once, which enhances responsiveness and facilitates more seamless user interactions.
28. How do you handle routing in a React application, and what are the advantages of using a routing library like React Router?
Libraries like React Router are frequently used to handle routing in React applications. With the declarative route definition feature offered by React Router, users can navigate between various application sections without having to completely reload the page. With capabilities like route guards, nested routes, and parameters, it’s a vital tool for building intricate single-page applications with obvious navigation.
29. What is the role of the useRef hook in React, and in what scenarios would you use it?
In React, the primary use of the useRef hook is to directly access and interact with DOM elements. Developers can access the properties and methods of DOM elements and obtain references to them. UseRef is useful for controlling focus, interacting with third-party libraries, and making necessary changes to the DOM, but it should be avoided in most situations to preserve React’s declarative design philosophy.
30. How can you optimize the performance of a React application that deals with a large dataset or frequent updates?
React applications with large datasets or frequent updates may benefit from the use of virtualization, which renders only the visible elements, pagination, memoization lazy loading, and server-side pagination or infinite scrolling. It’s critical to strike a balance between the requirement for data display and the need for an effective and responsive user experience.
31. Describe how you can optimize performance using React.memo and when to use it in functional components.
A higher-order component called React.memo is used to memorize the rendering of functional components. It does this by caching the result and only rendering the component again when its props change. Comparing old and new props effectively prevents needless re-renders in functional components. Functional components where performance optimization is required and re-rendering can be costly should use React.memo.
32. Explain the concept of Error Boundaries in React and their role in handling errors in the component tree.
React components known as Error Boundaries are designed to detect JavaScript errors that may occur in their child component tree during rendering, lifecycle operations, or constructors. They offer a means of handling errors with grace and keep the program from crashing altogether. Error Boundaries function by rendering a fallback user interface (UI) when errors arise inside their subtree, using the componentDidCatch lifecycle method.
33. What is the significance of the useReducer hook in React, and how does it differ from useState?
The useReducer hook is an alternative to useState for managing complex state logic in React. It’s more suitable for managing state transitions based on actions and helps in handling more complex state updates. While useState is used for simple state management, useReducer is preferred when state changes involve intricate logic and multiple sub-values.
34. What are the advantages of using TypeScript with React, and how does it improve the development process?
Static typing provided by TypeScript helps identify possible errors during development, which improves React development. It improves code documentation, enforces types, and activates IDE features like autocompletion and type inference, all of which increase predictability, readability, and maintainability of the codebase.