Top 50 ReactJS Interview Questions and Answers for Freshers 2023
Prepare for your ReactJS interview with this comprehensive list of the top 50 ReactJS interview questions and detailed answers for freshers in 2023. Enhance your knowledge of ReactJS concepts and optimize your interview performance.
If you’re a fresher preparing for a ReactJS interview in 2023, it’s crucial to be well-prepared and knowledgeable about the framework. In this article, we’ve compiled a comprehensive list of the top 50 ReactJS interview questions and provided detailed answers to help you excel in your interview. Whether you’re a self-taught developer or a computer science graduate, these questions cover essential concepts and topics you need to know. Let’s dive in and enhance your ReactJS interview readiness!
1. What is ReactJS?
ReactJS is an open-source JavaScript library used for building user interfaces. It allows developers to create reusable UI components and efficiently update and render them when the underlying data changes.
2. What are the key features of ReactJS?
Some key features of ReactJS include the virtual DOM, component-based architecture, one-way data flow, JSX syntax, and reusable UI components.
3. What is JSX?
JSX is a syntax extension for JavaScript that allows developers to write HTML-like code in their JavaScript files. It simplifies the process of creating and rendering React components.
4. What is the difference between ReactJS and React Native?
ReactJS is used for building web applications, while React Native is used for developing mobile applications for iOS and Android platforms.
5. What is the significance of the virtual DOM in ReactJS?
The virtual DOM is a lightweight copy of the actual DOM. ReactJS uses it to efficiently update and render components by comparing the changes between the virtual DOM and the real DOM, resulting in improved performance.
6. Explain the concept of components in ReactJS.
Components are reusable, independent pieces of code that encapsulate a part of the user interface. They can be class-based or functional, and they allow developers to create complex UI structures by composing smaller components.
7. What is the difference between class components and functional components?
Class components are created using ES6 classes and have additional features like lifecycle methods and state. Functional components are simpler and easier to write, and they are preferred when there is no need for state or lifecycle methods.
8. What is state in ReactJS?
State is a built-in object in ReactJS that represents the internal data of a component. It is mutable and can be changed using the setState() method, triggering a re-render of the component.
9. How does React handle data flow?
React follows a unidirectional data flow, where data flows from parent components to child components. Child components receive data through props and communicate with their parent components using callbacks.
10. What are props in ReactJS?
Props (short for properties) are used to pass data from a parent component to its child components. They are immutable and are passed as attributes to child components in JSX.
11. What are React hooks?
React hooks are functions that allow functional components to have state and lifecycle functionalities previously only available in class components. Some popular hooks include useState, useEffect, and useContext.
12. Explain the useEffect hook in React.
The useEffect hook is used to perform side effects in functional components. It runs after every render and can be used to handle tasks such as data fetching, subscriptions, or manually manipulating the DOM.
13. What is the purpose of the useState hook?
The useState hook is used to introduce state into functional components. It returns a state variable and a function to update that variable, allowing you to manage component state without using class components.
14. What is the significance of keys in React lists?
Keys are used to uniquely identify elements in a list of components. They help React efficiently update and re-render components by providing a stable identity for each item.
15. Explain the concept of prop drilling in React.
Prop drilling occurs when props are passed through multiple levels of components to reach a deeply nested component that needs access to the data. It can make the code more complex and harder to maintain.
16. How can you prevent prop drilling in React?
Prop drilling can be avoided by using React context. Context allows you to pass data through the component tree without explicitly passing props at every level.
17. What is React Router?
React Router is a popular library that enables routing and navigation in React applications. It allows you to define routes and render different components based on the current URL.
18. How do you handle forms in React?
In React, form handling involves using state to track form input values and handling form submission events. You can use controlled components by binding form inputs to state values or use libraries like Formik or React Hook Form for easier form management.
19. What is Redux, and why would you use it with React?
Redux is a predictable state container for JavaScript applications. It provides a central store to manage application state and enables predictable state updates through actions and reducers. Redux is commonly used with React for managing complex application states.
20. What is React context, and when would you use it?
React context is a feature that allows you to share data between components without explicitly passing props. It is used when you have data that needs to be accessed by many components at different levels of the component tree.
21. What is the purpose of the shouldComponentUpdate lifecycle method?
The shouldComponentUpdate method allows you to optimize performance by determining whether a component should re-render or not. By default, React re-renders components whenever there is a state or prop change.
22. What are higher-order components (HOCs)?
Higher-order components are functions that take a component and return an enhanced version of that component. They are used for code reuse, cross-cutting concerns, and adding additional functionality to components.
23. What are React hooks rules or guidelines to follow?
Some guidelines for using React hooks include:
- Only call hooks at the top level of functional components or custom hooks.
- Don’t call hooks inside loops, conditions, or nested functions.
- Always call hooks in the same order in every render.
- Make sure to provide a dependencies array in useEffect hooks.
24. Explain the concept of lazy loading in React.
Lazy loading is a technique used to load components or assets asynchronously when they are needed. It helps improve performance by reducing the initial bundle size and only loading components when they are required.
25. What is the significance of the React Fragment component?
The React Fragment component allows you to group multiple elements without adding an extra DOM element. It is useful when you need to return multiple elements from a component without introducing additional nodes in the DOM.
26. What is the purpose of the React Developer Tools extension?
The React Developer Tools extension is a browser extension that allows developers to inspect and debug React components. It provides a panel with a component tree, component state, and props information.
27. How do you handle errors in React components?
Errors in React components can be handled using error boundaries. Error boundaries are components that catch JavaScript errors anywhere in their child component tree and display fallback UI instead of crashing the whole application.
28. What are the different lifecycle methods in React?
The main lifecycle methods in React are:
- componentDidMount: Called after a component is mounted and rendered.
- componentDidUpdate: Called after a component is updated and re-rendered.
- componentWillUnmount: Called before a component is unmounted and destroyed.
29. What is the purpose of the useCallback hook?
The useCallback hook is used to memoize a function and prevent unnecessary re-creation of that function on every render. It is useful when passing callbacks to child components to avoid unnecessary re-rendering.
30. What is the role of the React.Fragment component?
The React.Fragment component is used to wrap multiple elements without creating an additional DOM node. It is commonly used when returning an array of elements or when you don’t want to introduce an extra parent element.
31. Explain the concept of code splitting in React.
Code splitting is a technique used to split the JavaScript bundle into smaller chunks and load them on demand. It helps reduce the initial loading time of an application by only loading the necessary code when it is needed.
32. What is the purpose of the useMemo hook?
The useMemo hook is used to memoize a value and prevent unnecessary re-computation. It is helpful when you have a costly computation that doesn’t need to be repeated on every render.
33. How do you handle side effects in React?
Side effects, such as data fetching or subscriptions, can be handled using the useEffect hook. You can specify the dependencies that trigger the effect and perform the necessary cleanup when the component is unmounted.
34. What is the purpose of the React.StrictMode component?
The React.StrictMode component is used during development to highlight potential problems in the application. It performs additional checks and warnings to help identify potential issues and ensure better code quality.
35. How can you optimize the performance of React components?
Some techniques to optimize React component performance include:
- Using React.memo or useMemo for memoization.
- Implementing shouldComponentUpdate or using PureComponent for optimized rendering.
- Avoiding unnecessary re-renders by using useCallback or useMemo for callbacks or computed values.
36. What is the purpose of the React.cloneElement method?
The React.cloneElement method is used to clone and return a new React element with modified props. It is useful when you need to add or modify props for a specific child component.
37. What are React portals?
React portals provide a way to render a component’s children into a DOM node that is outside the component’s parent hierarchy. It is useful when you need to render components into a different part of the DOM, such as modals or overlays.
38. What is the significance of the key prop in React lists?
The key prop in React lists is used to provide a unique identifier for each item in the list. It helps React efficiently update and re-render list items when their order or content changes.
39. Explain the concept of controlled and uncontrolled components in React.
Controlled components are components whose form data is controlled by React using state. Uncontrolled components store their form data in the DOM, and React retrieves the values when needed.
40. What is the purpose of the React.PureComponent class?
The React.PureComponent class is a base class for components that implement a shouldComponentUpdate method with a shallow prop and state comparison. It helps optimize performance by reducing unnecessary re-renders.
41. How can you handle asynchronous data fetching in React?
Asynchronous data fetching in React can be handled using libraries like Axios or the built-in fetch API. You can make the data fetching request in the useEffect hook and update the state when the data is received.
42. What is the role of the React.lazy function?
The React.lazy function is used for lazy loading components. It allows you to dynamically import a component when it is needed, reducing the initial bundle size and improving performance.
43. What is the purpose of the render prop in React?
The render prop is a technique used to pass a function as a prop to a component, allowing the component to render the result of that function. It is often used for code reuse and component composition.
44. How do you handle routing in a React application?
Routing in a React application can be handled using libraries like React Router or Reach Router. These libraries provide components and methods to define routes and render different components based on the current URL.
45. What are React hooks rules or guidelines to follow?
Some guidelines for using React hooks include:
- Only call hooks at the top level of functional components or custom hooks.
- Don’t call hooks inside loops, conditions, or nested functions.
- Always call hooks in the same order in every render.
- Make sure to provide dependencies array in useEffect hooks.
46. Explain the concept of lazy loading in React.
Lazy loading is a technique used to load components or assets asynchronously when they are needed. It helps improve performance by reducing the initial bundle size and only loading components when they are required.
47. What is the significance of the React.Fragment component?
The React.Fragment component allows you to group multiple elements together without adding an extra DOM element. It is useful when you need to return multiple elements from a component without introducing additional nodes in the DOM.
48. What is the purpose of the React Developer Tools extension?
The React Developer Tools extension is a browser extension that allows developers to inspect and debug React components. It provides a panel with a component tree, component state, and props information.
49. How do you handle errors in React components?
Errors in React components can be handled using error boundaries. Error boundaries are components that catch JavaScript errors anywhere in their child component tree and display fallback UI instead of crashing the whole application.
50. What are the different lifecycle methods in React?
The main lifecycle methods in React are:
- componentDidMount: Called after a component is mounted and rendered.
- componentDidUpdate: Called after a component is updated and re-rendered.
- componentWillUnmount: Called before a component is unmounted and destroyed.
In this article, we covered the Top 50 ReactJS interview questions and provided detailed answers for freshers in 2023. By studying and understanding these questions, you’ll be well-prepared for your ReactJS interview and demonstrate your knowledge and skills. Remember to practice coding and implementing React components to reinforce your learning. Good luck with your interview preparations!
