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React JS Interview Questions - Ace Your React Interviews in 2023



Introduction

In today's fast-paced digital landscape, user experience is paramount. React.js excels in this area, enabling developers to effortlessly create dynamic and interactive interfaces. Its virtual DOM and efficient rendering ensure speedy performance, delivering a seamless experience for users.

React.js enjoys strong industry support and a vibrant community. Prominent companies like Facebook, Instagram, and Airbnb rely on React.js for their applications. Consequently, the demand for React.js developers is high in the job market, making it a highly sought-after best programming language skill in 2023. 

In this blog, you will learn the following:

  • Master the answers to react js interview questions
  • Get MVP tips to reactjs interview questions and answers
  • Additional Resources to attend react js interview questions 2023

React JS Interview Questions and Answers for Freshers

As the demand for React.js developers continues to skyrocket, it's crucial to equip yourself with the knowledge and confidence to ace any interview. Here are the top 30 reactjs interview questions and answers for freshers in 2023.

1. What is React?

React is a popular JavaScript library used for building user interfaces. It allows developers to create reusable UI components and efficiently update the user interface when the underlying data changes. React follows a component-based architecture and uses a virtual DOM for efficient rendering. 

2. What is JSX?

JSX is a syntax extension for JavaScript that allows developers to write HTML-like code within JavaScript. It enables the blending of HTML and JavaScript, making it easier to describe the structure and appearance of React components. JSX code is transpiled into regular JavaScript by tools like Babel.

3. What are the features of React?

  • Component-based architecture
  •  Virtual DOM for efficient rendering
  • JSX syntax for easy component creation
  • Unidirectional data flow
  • Reusable and composable components
  • Support for server-side rendering
  • Strong developer community and ecosystem

4. What are the advantages of using React?

  •  Enhanced performance with the virtual DOM
  • Reusable components for efficient development
  • Unidirectional data flow simplifies debugging and maintenance
  • Support for server-side rendering for better initial loading speed and SEO
  • Active community and vast ecosystem of libraries and tools
  • Smooth integration with other libraries or existing projects

5. How is React different from Angular?

React and Angular are both popular JavaScript frameworks for building web applications, but they have some key differences:

  •  React is a library while Angular is a complete framework.
  • React uses a virtual DOM, while Angular uses a real DOM.
  •  React follows a component-based architecture, while Angular uses a hierarchical structure.
  •  React uses JSX for templating, while Angular uses HTML templates.
  •  React is more flexible and allows developers to choose additional libraries, while Angular provides a more opinionated approach.

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6. What is the Virtual DOM?

The Virtual DOM is a lightweight JavaScript object representation of the actual browser DOM. React uses the Virtual DOM to efficiently update and render components. When there are changes to the data, React calculates the difference between the previous and current Virtual DOM and applies only the necessary updates to the real DOM, resulting in improved performance.

7. What are the lifecycle methods of a React component?

This is one of the frequent react js interview questions in 2023. React components have several lifecycle methods that allow developers to hook into different phases of a component's life. The key lifecycle methods are:

  • componentDidMount()`: Invoked after the component is mounted (inserted into the DOM).
  • `componentDidUpdate()`: Invoked after the component is updated (re-rendered).
  • `componentWillUnmount()`: Invoked before the component is unmounted and destroyed.
  • `render()`: Responsible for rendering the component's JSX representation.
  • `shouldComponentUpdate()`: Determines if the component should re-render or not.

8. What are the different ways to create a React component?

There are two main ways to create a React component:

  • Functional Components: These are stateless components written as JavaScript functions. They receive props as arguments and return JSX elements.
  • Class Components: These are stateful components defined as JavaScript classes. They extend the `React.Component` class and have additional features such as lifecycle methods and state management.

9. What is state and props in React?

  • - State: State represents the internal data of a component. It is mutable and can be updated using `setState()`. State changes trigger re-rendering of the component and its child components.
  • - Props: Props (short for properties) are read-only values passed from a parent component to its child components. They are used to provide data or configuration to components.

10. What is the difference between state and props?

- State is managed within a component and can be changed, while props are passed from parent components and cannot be modified by the child components.

- State is used for internal component data and can trigger re-rendering when updated, whereas props provide data and configuration to components, allowing parent components to communicate with their children.

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11. How to pass props to a React component?

Props can be passed to a React component by adding attributes to the component when it is used in the parent component's JSX code. The values of these attributes become the props in the child component and can be accessed within the child component using `props`.

12. How to use state in a React component?

To use state in a React component, you need to define a state object within the component's class constructor using `this.state = { ... }`. You can then access and update the state using `this.state` and `this.setState()` respectively. When state changes, React automatically re-renders the component to reflect the updated state.

13. How to handle events in React?

In React, event handling is done by attaching event listeners to elements within components. Event handlers are defined as methods in the component class and are then assigned to the appropriate event using JSX. When the event occurs, the associated event handler is invoked, allowing you to perform the desired actions.

14. How to create a functional component in React?

A functional component in React is created by defining a JavaScript function that returns JSX elements. The function takes props as its parameter and uses them to render the component's output. Functional components are stateless and can be created using arrow functions or regular functions.

15. How to create a class component in React?

A class component in React is created by defining a class that extends the `React.Component` class. The component class must implement a `render()` method, which returns JSX elements representing the component's output. Class components can have state, lifecycle methods, and more advanced functionality compared to functional components.

16. What is the difference between functional and class components?

The main difference between functional and class components is the syntax and additional features they support. Functional components are simpler, written as JavaScript functions, and do not have state or lifecycle methods. Class components are defined as classes, and can have state, lifecycle methods, and other features like component-level methods.

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17. What is React Router?

React Router is a popular routing library for React applications. It allows developers to handle navigation and routing within a single-page application (SPA). React Router provides declarative routing through components, enabling the rendering of different components based on the current URL or route.

18. What is Redux?

Redux is a predictable state management library for JavaScript applications, including React. It provides a central store that holds the application state and allows components to access and update the state through actions and reducers. Redux helps manage complex application states and enables predictable data flow.

19. What is React Native?

React Native is a framework developed by Facebook that allows developers to build native mobile applications using React and JavaScript. It uses native components for rendering, resulting in highly performant and truly native mobile apps for both iOS and Android platforms.

20. What are the best practices for writing React code?

  • Organize your code into reusable and modular components.
  •  Follow the single responsibility principle and keep components focused.
  •  Use meaningful and descriptive naming conventions.
  • Utilize functional components whenever possible.
  • Keep state management simple and localized.
  • Write unit tests for your components and application logic.
  • Optimize performance by using memoization and avoiding unnecessary re-renders.
  •  Follow established coding conventions and style guidelines.
  • Leverage popular libraries and tools to streamline development processes.

21. What are the different types of React components?

There are mainly two types of React components:

  •  Functional Components: These are stateless components written as JavaScript functions. They receive props as arguments and return JSX elements. Functional components are easier to read, test, and maintain.
  •  Class Components: These are stateful components defined as JavaScript classes. They extend the `React.Component` class and have additional features such as lifecycle methods and state management. Class components are useful when you need to manage an internal state or use lifecycle methods.
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22. What is the difference between stateless and stateful components?

  • Stateless components, also known as functional components, do not have an internal state. They receive data via props and render the output based on the given props. They are primarily responsible for presenting data and receiving user input.
  • Stateful components, also known as class components, have an internal state managed using `this.state`. They can modify their state using `setState()` and trigger re-renders based on the updated state. Stateful components are used when a component needs to maintain and manage its own data.

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23. What is the difference between class and functional components?

The key differences between class and functional components are as follows:

  • Syntax: Class components are defined as JavaScript classes, while functional components are defined as JavaScript functions.
  • State and Lifecycle: Class components can have state, manage their own lifecycle methods, and have access to lifecycle methods like `componentDidMount()` and `componentDidUpdate()`. Functional components do not have lifecycle methods or state management.
  • Complexity: Functional components are simpler, easier to read, and generally preferred for their simplicity. Class components are useful when you need to manage state or use lifecycle methods.

24. What is the use of React.PureComponent?

React.PureComponent is a base class provided by React that is similar to a regular class component. However, it includes a built-in implementation of `shouldComponentUpdate()` that performs a shallow comparison of the component's props and state. If there are no changes, it prevents unnecessary re-renders, optimizing performance.

25. What is the use of React.memo?

React.memo is a higher-order component (HOC) that memoizes the result of a functional component. It memorizes the rendered output and reuses it if the component's props remain the same, avoiding unnecessary re-renders. It is used to optimize functional components that may re-render frequently but don't rely on changes in props.

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26. What is the use of React.lazy?

React.lazy is a feature introduced in React 16.6 that enables code-splitting and lazy loading of components. It allows you to load a component lazily when it is needed, rather than including it in the initial bundle. This helps in reducing the bundle size and improving the initial loading speed of the application.

27. What is the use of React.Suspense?

React.Suspense is another feature introduced in React 16.6 that works together with React.lazy for code-splitting. It allows you to define fallback content to be displayed while the lazy-loaded component is being loaded. This fallback content could be a loading spinner or any other placeholder, providing a better user experience during component loading.

28. What is the use of React.Fragment?

React.Fragment is a component introduced in React 16 that allows you to return multiple elements without adding an extra wrapping element. It is useful when you want to render multiple elements in a component without introducing unnecessary wrapper divs or other elements.

29. What is the use of React.createElement? (continued)

such as when dynamically creating elements or when using React without JSX. It takes three arguments: the type of the element (e.g., HTML tag or custom component), optional properties or attributes for the element, and optional children elements.

30. What is the use of React.cloneElement?

React.cloneElement is a method provided by React that allows you to clone and modify a React element. It is typically used when you want to add or override props of a React element while maintaining its original type and key. This is useful when working with components that accept and modify their children's elements.

Here are the top Reactjs interview questions and answers for freshers, that will equip you with the necessary knowledge to ace your interviews. If you are looking for React js interview questions for experienced, below are the following.

React JS Interview Questions and Answers for Experienced

As React.js continues to dominate the tech landscape, employers are seeking top talent who can demonstrate a deep understanding of its intricacies. Here are our meticulously curated set of react js interview questions, to help you crack your next interview.

1. What are the performance benefits of using React?

React uses a virtual DOM, a lightweight representation of the actual DOM. This allows React to only update the actual DOM when necessary, which can lead to significant performance improvements. Additionally, React uses a unidirectional data flow, which helps to prevent race conditions and other performance issues.

2. How to optimize React components for performance?

There are a number of things you can do to optimize React components for performance. Some of the most important things include:

  • Using functional components instead of class components
  • Using pure components whenever possible
  • Avoiding unnecessary re-renders
  • Using memoization to cache expensive calculations
  • Using lazy loading for large components

3. How to test React components?

There are a number of ways to test React components. Some of the most popular methods include:

  • Unit testing
  • Integration testing
  • End-to-end testing

Unit testing is the most basic form of testing. It involves testing individual components in isolation. Integration testing tests how components interact with each other. End-to-end testing tests the entire application from start to finish.

4. How to debug React components?

Among the frequently asked React.js interview questions for experienced candidates, this one stands out. There are a number of ways to debug React components. Some of the most popular methods include:

  • Using the React DevTools
  • Using console.log()
  • Using breakpoints

The React DevTools are a powerful tool that can be used to inspect React components and their state. They can also be used to debug React components.

console.log() is a JavaScript function that can be used to print values to the console. This can be helpful for debugging React components.

Breakpoints can be used to stop the execution of a program at a specific point. This can be helpful for debugging React components.

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5. How to scale React applications?

These kinds of React js interview questions are popular in 2023 and is often inquired about during interviews with experienced individuals. There are a number of things you can do to scale React applications. Some of the most important things include:

  • Using a component library
  • Using a state management library
  • Using a routing library
  • Using a testing library

A component library can help you to create reusable components. This can help to improve the maintainability and scalability of your application.

A state management library can help you to manage the state of your application. This can help to improve the performance and scalability of your application.

A routing library can help you to manage the navigation of your application. This can help to improve the user experience and scalability of your application.

A testing library can help you to test your application. This can help to improve the quality and scalability of your application.

6. How to work with React in a team environment?

There are a number of things you can do to work with React in a team environment. Some of the most important things include:

  • Using a version control system
  • Using a code review process
  • Using a communication tool

A version control system can help you to track changes to your code. This can help to prevent conflicts and improve collaboration.

A code review process can help you to find and fix errors in your code. This can help to improve the quality of your application.

A communication tool can help you to communicate with your team members. This can help to improve collaboration and productivity.

7. How to use React with other libraries and frameworks?

This is one of the most asked react js interview questions for experienced. React can be used with a variety of other libraries and frameworks. Some of the most popular libraries and frameworks that can be used with React include:

  • Redux
  • React Router
  • React Native

Redux is a state management library that can be used with React. It can help you to manage the state of your application in a centralized way.

React Router is a routing library that can be used with React. It can help you to manage the navigation of your application.

React Native is a framework that can be used to build native mobile applications using React.

8. What are the latest trends in React?

Some of the latest trends in React include:

  • Hooks
  • Suspense
  • Context
  • Incremental Static Regeneration (ISR)

Hooks are a new way to write React components. They allow you to use state and other React features without having to use class components.

Suspense is a new feature that allows you to lazy load components. This can help to improve performance.

Context is a new way to share data between components. It can help to improve code reuse and reduce boilerplate code.

Incremental Static Regeneration (ISR) is a new feature that allows you to pre-render parts of your application. This can help to improve performance.

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9. What are the challenges of using React?

Some of the challenges of using React include:

  • Learning curve
  • State management
  • Performance
  • Testing

Learning curve

React can be a bit challenging to learn, especially for developers who are not familiar with JavaScript frameworks. There are a lot of concepts to learn, such as components, state, and props.

State management

Managing state in React can be a challenge. There are a number of different state management libraries available, each with its own pros and cons. It can be difficult to choose the right state management library for your application.

Performance

React can be a bit slow, especially for large applications. There are a number of things you can do to improve the performance of your React application, such as using functional components, using pure components, and using memoization.

Testing

Testing React applications can be a challenge. React components are often deeply nested, which can make it difficult to test them effectively. There are a number of different testing libraries available, each with its own pros and cons. It can be difficult to choose the right testing library for your application.

10. What are your thoughts on the future of React?

(Sample Answer) 

I believe that React has a bright future. It is a powerful and versatile framework that is used by a large number of developers. React is constantly being improved, and I believe that it will continue to be a popular choice for building user interfaces in the years to come.

Here are some of the reasons why I believe that React has a bright future:

  • Large community: React has a large and active community of developers. This means that there are many resources available to help you learn and use React.
  • Popularity: React is one of the most popular JavaScript frameworks in the world. This means that there are many jobs available for React developers.
  • Ease of use: React is easy to learn and use. This makes it a good choice for both beginners and experienced developers.
  • Performance: React is very performant. This means that it can be used to build fast and responsive user interfaces.
  • Flexibility: React is very flexible. This means that it can be used to build a wide variety of user interfaces.
  • Scalability: React is very scalable. This means that it can be used to build large and complex user interfaces.

I believe that these factors will contribute to the continued growth and popularity of React in the years to come.

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11. What are the pros and cons of using React Router?

Pros:

  • React Router is a powerful routing library that can be used to manage the navigation of your React application.
  • It is easy to use and learn.
  • It is well-documented and supported.
  • It is used by a large number of developers, which means that there is a large community of support available.

Cons:

  • React Router can be a bit complex to use, especially for large applications.
  • It can be difficult to debug React Router applications.
  • There are a number of other routing libraries available, each with its own pros and cons. It can be difficult to choose the right routing library for your application.

12. What are the pros and cons of using Redux?

Pros:

  • Redux is a powerful state management library that can be used to manage the state of your React application.
  • It is easy to use and learn.
  • It is well-documented and supported.
  • It is used by a large number of developers, which means that there is a large community of support available.

Cons:

  • Redux can be a bit complex to use, especially for large applications.
  • It can be difficult to debug Redux applications.
  • There are a number of other state management libraries available, each with its own pros and cons. It can be difficult to choose the right state management library for your application.

13. What are the pros and cons of using React Native?

Pros:

  • React Native is a powerful framework that can be used to build native mobile applications using React.
  • It is easy to learn and use.
  • It is well-documented and supported.
  • It is used by a large number of developers, which means that there is a large community of support available.

Cons:

  • React Native can be a bit complex to use, especially for large applications.
  • It can be difficult to debug React Native applications.

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14. What are the best practices for writing React code that is both performant and maintainable?

Here are some best practices for writing React code that is both performant and maintainable:

  • Use functional components instead of class components.
  • Use pure components whenever possible.
  • Avoid unnecessary re-renders.
  • Use memoization to cache expensive calculations.
  • Use lazy loading for large components.
  • Use a component library.
  • Use a state management library.
  • Use a routing library.
  • Use a testing library.
  • Write unit tests.
  • Write integration tests.
  • Write end-to-end tests.
  • Use a version control system.
  • Use a code review process.
  • Use a communication tool.

15. What is your favorite React library or framework?

(Sample Answer) My favorite React library is React Router. I think it is a very powerful and easy-to-use library for managing the navigation of React applications. Further, in these kind of react js interview questions the answers need to be concise clear and to the point which creates a quality impression on recruiters. 

16. What is your least favorite React library or framework?

(Sample Answer) 

I don't have a least favorite React library or framework. I think all of the React libraries and frameworks that I have used are very good. However, if I had to choose one that I use the least, it would be React Router. I think React Router is a great library, but I find that I don't need it very often. Most of the applications that I build are relatively simple, and I can get away with using the built-in routing features of React.

Another reason why I don't use React Router very often is that I find it can be a bit complex. There are a lot of different concepts to learn, and it can be easy to get lost in the documentation.

Overall, I think React Router is a great library, but it's not something that I use very often. If you're building a complex application with a lot of routing, then React Router is a great option. However, if you're building a simpler application, then you may be able to get away with using the built-in routing features of React.

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17. What is one thing you would change about React?

(Sample Answer)  If I could change one thing about React, it would be the way that state is managed. I think that React's current state management system is a bit complex and can be difficult to learn. I would like to see a simpler state management system that is easier to learn and use.

18. What are the pros and cons of using React hooks?

React hooks are a new feature that was introduced in React 16.8. They allow you to use state and other React features without having to use class components.

Pros of using React hooks:

  • Concise and easier to read: Hooks are more concise and easier to read than class components. This is because they are written as functions, which are more familiar to JavaScript developers.
  • More flexible: Hooks are more flexible than class components. This is because they can be used to implement a wider range of functionality.
  • Easier to test: Hooks are easier to test than class components. This is because they are written as functions, which can be unit tested more easily.
  • Cons of using React hooks:
  • Not as well-documented: Hooks are not as well-documented as class components. This can make it difficult to learn how to use them.
  • Can be more difficult to debug: Hooks can be more difficult to debug than class components. This is because they are more complex and there are more things that can go wrong.

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19. How would you implement a custom hook?

To implement a custom hook, you first need to define a function that takes in some props and returns some state. You can then use the state and props in the function to perform some action. For example, you could create a custom hook that takes in a list of items and returns a function that renders a list of those items.

Here is an example of a custom hook that takes in a list of items and returns a function that renders a list of those items:

20. What are the best practices for writing performant React code?

The best practices for writing performant React code are to:

  • Use functional components
  • Use pure components whenever possible
  • Avoid unnecessary re-renders
  • Use memoization to cache expensive calculations
  • Use lazy loading for large components

Functional components: Functional components are more performant than class components because they do not have to create a new instance of a class every time they are rendered.

Pure components: Pure components are more performant than impure components because they only re-render when their props or state change.

Avoid unnecessary re-renders: Unnecessary re-renders can make your React code less performant. To avoid unnecessary re-renders, you can use the shouldComponentUpdate method to check if your component needs to be re-rendered.

Memoization: Memoization is a technique that can be used to cache expensive calculations. This can improve the performance of your React code by avoiding the need to recalculate the same value multiple times.

Lazy loading: Lazy loading is a technique that can be used to load large components only when they are needed. This can improve the performance of your React code by avoiding the need to load large components that are not visible on the screen.

To wrap up, this section has presented a comprehensive compilation of Reactjs interview questions and answers for experienced. Armed with this knowledge, you are now better equipped to confidently navigate React js interview questions 2023 and demonstrate your proficiency in this widely-used JavaScript library.

5 Tips Improve your React JS Interview Performance

In 2023, React.js continues to dominate the market, making it a highly sought-after skill for aspiring developers and seasoned professionals alike. To help you excel in React.js interviews and showcase your expertise, here are some of the best strategies:

1. Sharpen your understanding of React.js fundamentals:

  • Grasp the core concepts of components, props, and state management.
  • Familiarize yourself with JSX and its differences from HTML.
  • Gain a solid understanding of React.js lifecycle methods and their usage.

2. Stay updated with the latest React.js trends and best practices:

  • Keep up with the evolving React.js ecosystem and new features.
  • Stay informed about the latest community-driven libraries and tools.
  • Stay updated with the latest reactjs interview questions.
  • Follow industry blogs, forums, and social media channels for insights and updates.

3. Practice building real-world projects with React.js:

  • Implement a variety of React.js applications to reinforce your skills.
  • Develop projects that demonstrate your understanding of state management, routing, and form handling.
  • Showcase your ability to optimize performance and deploy React.js applications.

4. Gain hands-on experience with popular state management libraries:

  • Explore and utilize state management libraries like Redux or MobX.
  • Understand how to effectively manage application state and handle complex data flows.
  • Demonstrate your expertise in integrating state management solutions into React.js applications.

5. Prepare for technical interview questions and coding challenges:

  • Familiarize yourself with common interview questions related to React.js.
  •  Practice coding exercises to strengthen your problem-solving skills.
  • Be ready to explain your thought process and showcase your ability to write clean and efficient React.js code.

By following these masterful tips, you can boost your confidence, deepen your React.js knowledge, and greatly improve your performance in React.js interviews. Also, you can join our core Java training program to enhance your skills and stand out among the best.

Conclusion

Congratulations! You now possess a comprehensive understanding of react js interview questions. By mastering Reactjs interview questions, you unlock the potential to create remarkable user experiences, build scalable applications, and stand out in web development's competitive world.

Remember, React.js is more than a library; it's a powerful tool to bring your ideas to life and make a lasting impact in the digital landscape. Stay curious, continue learning, and stay updated with the latest trends and best practices as you journey with React.js.

Whether you're a fresher aiming for your first React.js job or an experienced developer looking to enhance your skills, these interview insights provide the knowledge to confidently navigate React.js interviews. Stay proactive in building real-world projects, implementing best practices, and refining problem-solving abilities. Leverage the resources available in the React.js community for continuous growth.

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Frequently Asked Questions

Q1. Can I use React without JSX?

Ans:- Yes, React can be used without JSX. JSX is a syntactic extension of JavaScript that allows you to write HTML-like code within JavaScript. However, React provides an alternative way to create elements using the `React.createElement` function, which takes the element type, props, and children as arguments. To learn more you can scroll above and read Reactjs interview questions and answers.

Q2. How do I pass data between parent and child components in React?

Ans:-  Data can be passed from a parent component to a child component in React using props. The parent component can pass data as props when rendering the child component. The child component can access and use the data by accessing `props` within its function or class definition.

Q3. What is the purpose of keys in React lists?

Ans:-  Keys in React lists help identify each item in a list uniquely. They assist React in efficiently updating and reordering list items. When rendering a list, it's important to provide a unique key prop to each item, usually using a stable and unique identifier associated with the item, such as an ID.

Q4.  How can I handle forms in React?

Ans:- Handling forms in React involves capturing user input, managing the form state, and performing actions based on the form data. You can use controlled components, where form inputs are controlled by React state, and event handlers are used to update the state. Alternatively, you can use libraries like Formik or React Hook Form to simplify form handling and validation.

Q5. What is the significance of the useEffect hook in React?

Ans:- The useEffect hook in React handles side effects in functional components. It allows you to perform actions such as data fetching, subscriptions, or DOM manipulation after the component has been rendered. The useEffect hook takes a function as its first argument and executes it after each render. It can also handle cleanup by returning a function. Also you can take a look at other reactjs interview questions above to get complete insight. 

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