25 Most Important Interview Questions and Their Correct Answers for React Js in 2023

In search of relevant interview queries for a React developer? The key lies in posing the right questions that are directly linked to the role, with the aim of evaluating whether the candidate is suitable. Some examples of useful questions involve:

• Can you share your familiarity with React JS?
• On a scale of proficiency, how do you rate your skills in composing and testing React components?
• Can you elaborate on the hurdles you have encountered while working with React?
• Share with us a past project you were involved in that utilized React.
• Kindly furnish us with an instance of a React application you have developed.
• What is your approach to managing state in React?
• Are you well acquainted with the best practices associated with React?
• Could you shed some light on how you have integrated React into pre-existing projects?
• What are some measures you have taken to improve the performance of React applications?
• What is your previous involvement in working with React Native?

Attempt to obtain answers to these inquiries and keep up with your learning.

Introduction

React is a JavaScript library that allows developers to design lightweight, responsive and scalable web applications. It was created by Jordan Walke, a Facebook software engineer, and is highly modular, making it easy to tailor to individual needs. Facebook initially implemented React in 2011 for their news feed, and later in 2012, Instagram also adopted this technology.

React has rapidly become a popular choice among developers for building web applications due to its user-friendliness. As a result, more and more businesses are adopting React’s technology, resulting in a growing need for skilled and experienced React JS developers. To remain competitive, companies should consider hiring professionals with the necessary know-how in the React JS framework.

Despite the abundance of competition for talented React JS developers, finding and recruiting the most capable candidates can still prove tricky. Therefore, it is crucial to have a well-planned recruitment strategy in place in order to attract top-tier engineers. Additionally, no recruitment process is complete without a thorough selection of interview questions.

Whether you are a recruiter or a developer, it is crucial to have a sound understanding of the top 25 commonly asked React JS interview questions and their corresponding answers in 2023. This knowledge will help you to be adequately prepared for any potential interview situation.

Below are the solutions to the most popular 25 React JS interview questions.

1. What is the meaning of “JSX” in React?

   JSX is short for “JavaScript XML.” React uses JavaScript’s standard extension, JSX, to fully explore its capabilities.
   
   JSX allows a simplified syntax that combines HTML and JavaScript elements, making it simple to create easy-to-read HTML documents and enhance program efficiency.

2. Is it possible to open JSX files in web browsers?

   Browsers are unable to read JSX files in their current state because they can only interpret JavaScript objects. To make a JSX file comprehensible to browsers, it must be translated into a JavaScript object through the use of JSX transformers. Essentially, JSX transformers are necessary to convert a JSX file into a format that can be interpreted by a browser.

3. What exactly is React’s Flux concept?

   Facebook frequently employs the Flux architecture for developing web applications that are distributed to end-users’ devices. Flux collaborates with React and adheres to the principle of unidirectional data flow, but it is not a library or a framework.

4. What is Redux, and how would you define it?

   Redux is a JavaScript library that is open-source and is used for developing user interfaces. It works as a container to save data and program configurations, and provides a framework for managing program state effectively across several environments. Redux is suitable for applications that require frequent updates and alterations and provides the possibility of scalability and long-term sustainability.

5. What is the purpose of Redux’s “Store” function?

   Redux’s ‘Store’ function allows developers to centralize the state of their entire application in one location. This approach consolidates the application’s different components and can result in automatic updates to the store. Furthermore, having one integrated state tree makes version tracking and debugging processes more efficient and straightforward.

6. What is the definition of an “action” in Redux?

   In Redux’s state management technique, action objects are utilized to transfer data between a program and its store. These objects typically include the action type and any relevant data. Only user-generated data is transmitted to the store.

7. What are some of the standout characteristics of React?

   The notable features of React are as follows:
   
   1. Time-saving
   2. Reduces time-to-market
   3. Provides convenience for future work
   4. Complete support from Meta
   5. Ensures code consistency through unidirectional data binding
   6. Offers an extensive range of features

8. What is Virtual DOM, and how does it work?

   The Virtual DOM, a lightweight JavaScript object, serves as a copy of the original Document Object Model (DOM). The DOM can store data in nodes, which are organized hierarchically with unique object properties identifying different elements, attributes, and content.
   
   In React JS, the render() method is responsible for creating a node tree from React components. As data models are updated through various user and system interactions in the development phase, the tree is also updated and modified accordingly.
   
   Here are the steps to using the virtual DOM:
   

   1. Step 1:

      Whenever there are modifications to the underlying data, the entire UI is re-rendered in Virtual DOM form.

   2. Step 2:

      The system evaluates the extent of the difference between the previous and new DOM representations.

   3. Step 3:

      Following the calculations, the real DOM is updated to mirror the recent changes in data.

9. What is the difference between the Real DOM and the Virtual DOM?

   The Contrast Between Physical and Digital DOM
   

   1. Changing the Document Object Model:

      The real DOM may exhaust your expenses, while the virtual DOM is comparatively inexpensive.

   2. Concrete Enhancements:

      When an element is altered, the real DOM creates a new DOM. In contrast, Virtual DOM updates the DOM instead of updating the JSX.

   3. No Long-Term Memory:

      In contrast to the memory-less virtual DOM, the real DOM necessitates a significant amount of RAM.

   4. Rate of Modification:

      The actual DOM takes time to update, while the virtual DOM provides more rapid modifications.

   5. HTML Modifications:

      Although the virtual DOM cannot alter HTML directly, the real DOM has the capability to do so.

10. What is the lifecycle of React components?

    The React component lifecycle consists of the following methods:
    

    1. componentDidMount():

       Executes on the client-side when the initial rendering is completed.

    2. componentDidUpdate():

       Triggered immediately after the completion of DOM rendering.

    3. componentWillMount():

       Executes on both client and server just prior to rendering commencement.

    4. componentWillReceiveProps():

       Invoked prior to the subsequent render call once the parent class has been received props.

    5. componentWillUnmount():

       Clears the memory and is triggered just after the component is unmounted from the DOM.

    6. componentWillUpdate():

       Conducted immediately before the rendering of the DOM.

    7. shouldComponentUpdate():

       The output can be either true or false. Typically, it returns false, but if the update is required, it must be modified to return true.

11. What are the advantages of employing a React router over a traditional one?

    Here are the distinctions between a React router and a conventional one:
    

    1. Changes to the URL:

       The traditional routing approach requires sending an HTTP request to the server in order to obtain the corresponding HTML page.

    2. Navigation:

       In traditional routing, users have to navigate through various webpages to access different views or perspectives. In contrast, React routing provides a seamless experience, giving visitors the impression of moving between webpages when in reality, they remain on the same page. This efficient routing methodology offers users a smooth and user-friendly experience.

    3. Pages:

       While traditional routing employs the same file for each view, React routing has a distinct file for each view.

12. When comparing two teams, how do “props” differ from “stats”?

    Here’s how “advantages” and “statistics” differ:
    
    1. Modifications to props are allowed within child components, but modifications to the state are not permissible.
    2. The component’s internals can be modified via the state, but not the props.
    3. When a parent component employs the state, the value cannot be altered.

13. Can you clarify the contrast between Redux and Flux?

    Here’s how Redux and Flux differ:
    

    1. Dispatcher:

       Unlike Flux, Redux does not include a dispatcher. Flux utilizes a centralized dispatcher instead.

    2. Retail Outlets:

       One key difference between Flux and Redux is that Flux comprises several stores, whereas Redux only has one.

    3. State:

       While state alterations are permitted in Flux, they are prohibited in Redux.

    4. Store:

       In Flux, the store is dynamic because it includes both state and transition logic. In comparison, Redux divides the storage and updating mechanisms into distinct components.

    5. Format of Store:

       In Flux, all currently open stores are distinct and shallow, which is not the case with Redux.

14. What is meant by the statement “In React, everything is a component?”

    React applications build their user interfaces (UIs) by dividing them into individual, self-contained components. This modular approach aids organization, as each component can be separately developed and tested before being integrated into the larger app, ensuring a robust and efficient UI that delivers optimal user experience.
    
    Since React displays each component independently from the others, the rendering of a single component has no impact on the overall UI of the app.

15. What is React’s modular and component-based design?

    React’s component-based system is the basis upon which application user interfaces are built. Once the system is established, each individual component can be repurposed and works autonomously, independent of the other components. This ensures that UI components can be quickly presented without the need for additional UI elements.

16. What is the process for rendering in React JS?

    In order for each component in React JS to function correctly, it must be rendered.
    
    When the render() method is executed, a Document Object Model (DOM) element is generated that represents the component. Web developers can efficiently render many HTML elements simultaneously by gathering the tags and then applying the render function to the objects.

17. What are states in React?

    In ReactJS, states are generally regarded as data sources or objects that manage various aspects of component behavior and rendering. States make it simple and effortless to create dynamic, interactive components.

18. What is a React higher-order component?

    Many React developers choose to utilise higher-order components (HOCs) to take advantage of the benefits of code reuse and abstraction layers. The React API includes HOCs as a common pattern, providing developers with a powerful tool for quickly and efficiently implementing component reuse logic.
    
    By utilising higher-order components (HOCs), developers can share behaviors among all React components, making the process simple and straightforward. This, in turn, enhances the overall application’s effectiveness and usability.

19. What is the ‘create-react-app’ command in React, and how does it work?

    React’s ‘create-react-app’ command provides a straightforward command-line interface (CLI) for developing React apps. By employing this CLI, users can concentrate on developing their application code, rather than configuring supplementary tools.

20. What are the benefits of using create-react-app in React?

    Advantages of the create-react-app command in React
    
    1. The amalgamation of Flow Statements, ES6, and JSX
    2. Pre-existing auto-prefixed CSS
    3. Modules for swift interactivity evaluation
    4. Real-time web-based debugging tools for development
    5. Scripts to handle JSS, CSS, and other types of files

21. What are “synthetic events” in React?

    Synthetic events are React objects that act as cross-browser wrappers for native events. This technique guarantees that the application programming interface (API) is compatible with various web browsers and that all necessary attributes are included in the event.

22. What do you mean by “stateful components” in the context of React?

    In computing, “stateful components” are capable of sensing and preserving changes.

23. What are “refs” in React?

    “Refs” in React refer to references. Refs enable the saving of a specific React element or component’s reference using the render function to return the reference.
    
    The most common scenarios where a reference is utilised are as follows:
    
    1. As a method of initiating required animations
    2. For the purpose of incorporating external DOM libraries
    3. With the objective of managing focus and implementing media application

24. What are “controlled components” in React?

    Controlled components in React are those that are capable of storing and retrieving their own state. The parent component owns all of the data and can be accessed via properties. To notify developers of any changes in the state, controlled components rely on callbacks.

25. Are there any limitations in React?

    React comes with various limitations, including:
    
    1. It is not exactly a framework, but rather a library.
    2. It would require a considerable amount of time to browse through and comprehend the entire library.
    3. This can be rather perplexing.
    4. It is especially valid while using inline templating and JSX, which makes programming more complex.

Nevertheless, in the end

Before answering any inquiries connected to React and JavaScript, it is strongly advised to have a solid grasp of the basics of both technologies. To ensure an optimal understanding of the subject matter, it is important to read extensively and reinforce knowledge.

As a recruiter, it is vital to establish a thorough and efficient interview process irrespective of the recruitment technique employed. To guarantee the best candidates are recruited, it is of utmost importance that the interviewers are knowledgeable enough to ask fundamental as well as advanced questions related to React JS.

If you’re encountering difficulties in recruiting React JS engineers and are struggling to find a concrete plan, consider giving Works a try.

When it comes to recruitment, Works is well-prepared to meet the staffing requirements of companies of all sizes. With Works, firms can quickly locate and recruit proficient React JS developers within a timeframe of merely three to five business days.

FAQs

Could you suggest some questions that I should pose to my React developer?

Listed below are some typical themes for React JS interviews.

• What is ReactJS in detail?
• What is the primary area of application for ReactJS?
• Do you begin with React or the back end first?
• What is the reason for React’s use of JSX?
• Could you specify the complete expansion of JSX?
• Are HTML and CSS relevant for React?

The question at hand is, “What are the appropriate queries to ask during a React JS interview?”

Incorporate some non-technical questions along with the technical ones.

15 Recommended Inquiries for a React JS Technical Interview

• Could you explain what the Virtual DOM is?
• The query is, “What are the steps to develop a React app?”
• What is the definition of an event in React?

Non-technical inquiries to include in a React JS interview:

• What are your limitations and weaknesses?
• How do your qualifications support your candidacy for this job?
• Could you provide a valid cause for leaving your prior job?

Can you please provide me with the basic details on React JS?

React JS is a popular open-source front-end web development library, which provides pre-built UI components that developers can use to create intuitive user interfaces quickly. A community of freelance developers and IT firms offer ongoing support and maintenance for this library.