Updated September 5, 2023
Introduction to ReactJS Interview Questions and Answers
ReactJS is a JavaScript library that is used for building user interfaces. Facebook and an individual group of developers maintain it.
ReactJS is one of the top in-demand skills for web developers, primarily front-end and full-stack developers. As such, a front-end developer earns an average base salary of $129,145 per year. Hence, preparing well for ReactJS interviews can open various job prospects for candidates.
ReactJS is used as a base for a single webpage or mobile application. It deals with the view layer of an application. It is also used for creating reusable UI components. We also assist developers in building extensive applications where data can be changed without refreshing. The main advantage of ReactJS is it is fast, scalable, and straightforward.
Table of Contents
Key Highlights
- ReactJS interview questions involve core concepts such as JSX, state, props, and component lifecycle.
- Experience building real-world applications using ReactJS can help demonstrate practical knowledge and problem-solving skills to the interviewer.
- Familiarity with popular ReactJS libraries and tools such as Redux, React Router, and Webpack can be an added advantage.
- Good knowledge of JavaScript and ES6 features is essential to write clean and efficient code while working with ReactJS.
- Excellent communication and collaboration skills and a willingness to learn and adapt to new technologies can help make a good impression on the interviewer.
Part 1 – ReactJS Interview Questions (Basic)
This first part covers basic ReactJS Interview Questions and Answers:
Q1. What is React?
Answer: React is a JavaScript library used for building user interfaces. ReactJS is used as a base of a single webpage or mobile application. It deals with the view layer of an application.
2. What is ReactJS used for?
Answer: ReactJS is a JavaScript library used for building user interfaces. It allows developers to create reusable UI components and manage the state of an application in a way that is efficient and easy to understand.
Q3. What is JSX?
Answer: JSX is simple JavaScript that allows HTML syntax and other HTML tags in the code. HTML syntax is processed into JavaScript calls of the React framework.
Q4. What is FLUX in ReactJS?
Answer: Flux is an application architecture in React View Library that Facebook designed for creating data layers in an application based on JavaScript.
Q5. What are Props and States in React?
Answer: Props mean the arguments’ properties passed in the JavaScript function. A state is used for creating a dynamic and interactive component.
Q6. What are refs in React?
Answer: For focus management and trigger animation, one uses refs in React. It also contains third-party libraries.
Q7. What is the difference between ReactJS and AngularJS?
Answer:
| ReactJS | AngularJS |
| A JavaScript library for building user interfaces. | A full-featured JavaScript framework for building large-scale, complex web applications. |
| It uses a virtual DOM to update the actual DOM efficiently. | It uses a two-way data binding approach, where any changes to the model automatically update the view and vice versa. |
| Follows a unidirectional data flow, where data flows only in one direction, from parent to child components. | Follows a bidirectional data flow, where changes in the view automatically update the model, and changes in the model automatically update the view. |
| It provides more flexibility and control, allowing developers to use any other library or framework alongside it. | It provides a complete solution for building web applications, including many built-in features like routing, forms, and animations. |
| A good understanding of JavaScript is required as it relies heavily on it. | It relies more on declarative templates and requires less JavaScript knowledge. |
Q8. How is flux different from Redux?
Answer:
| Flux | Redux |
| Flux is an architectural pattern that Facebook introduced. | Redux is a predictable state container that is based on Flux architecture. |
| Flux’s single dispatcher receives actions and dispatches them to the stores. | The store receives dispatched actions directly, as Redux has no dispatcher. |
| Flux has multiple stores that contain the application state. | Redux has a single store that contains the entire application state. |
| Flux stores can have mutable states and be changed anywhere in the application. | Redux stores have an immutable state; the only way to change the state is by dispatching an action. |
| Flux has more boilerplate code and requires more setup. | Redux has less boilerplate code and is easier to set up. |
Q9. What do you mean by a functional component in React?
Answer: A functional component is a component that returns React elements as an element.
Q10. What is routing?
Answer:
- The ability to switch between various pages or views of an application is called routing in React.
- The React Router library implements routing in React applications.
- Developers can design routes using essential components and properties because they support declarative routing.
- Moreover, React Router has a variety of routing components, including <BrowserRouter> and <Link>, that make it simple to design and switch between routes.
- Routing is integral to building complex React applications, as it allows for better organization and separation of concerns between different parts of an application.
Q11. What are the components of Redux?
Answer: Action, Reducer, Store, and View are the components of Redux.
- Action: Describes a user’s intent in the form of an object.
- Reducer: A pure function that receives the current state and an action and returns a new state.
- Store: A centralized place to store the state of an application.
- View: The user interface of an application.
Part 2 –ReactJS Interview Questions (Advanced)
Following are advanced ReactJS Interview Questions:
Q1. List the characteristics of ReactJS.
Answer:
- JSX: ReactJS has JSX. JSX is simple JavaScript that allows HTML syntax and other HTML tags in the code. The React framework processes HTML syntax into JavaScript calls.
- React Native: It contains a native library that supports Native iOS and Android applications.
- Simplicity: It is straightforward to grab. Its component-based approach and well-defined lifecycle are direct to use.
- Easy to Learn: Anyone with basic programming knowledge can quickly learn ReactJS. To learn ReactJS, one needs to know the basics of HTML and CSS.
- Data-Binding: ReactJS uses one-way data binding and application architecture controls data flow via a dispatcher.
- Testability: The ReactJS application is straightforward to test. Its views are easy to configure and can be treated as an application.
Q2. What are the lifecycle methods of React Components in detail?
Answer: Some of the most important lifecycle methods are given below:
- componentWillMount()
- componentDidMount()
- componentWillRecieveProps()
- shouldComponentUpdate()
- componentWillUpdate()
Q3. What is the lifecycle of ReactJS?
Answer: Initialization, State/Property updates, and Destruction are the lifecycle components of ReactJS.
Q4. What are the advantages of ReactJS?
Answer:
- Increased application performance.
- Client and Server side building.
- Reliable due to JSX code.
- Easy testing.
Q5. Which company developed React? When was it released?
Answer: Facebook developed ReactJS and developed it in March 2013.
Q6. What is the significance of the virtual DOM in ReactJS?
Answer: In ReactJS, the virtual DOM is a lightweight copy of the actual DOM, which helps to enhance the application’s performance. Whenever there is a change in the state of a React component, the virtual DOM compares the new and previous states and creates a list of minimum necessary changes. It then updates the actual DOM with these changes, resulting in faster rendering and improved user experience.
Q7. What is the basic difference between pros and state?
Answer:
| Aspects | Props | State |
| Definition | Short for “properties,” passed from parent component to child component. | User interactions or other events can change a component’s internal state over time. |
| Immutable | Immutable (cannot be modified by the component receiving them) | Mutable (can be adjusted using setState()) |
| Update Trigger | It can only be updated by the parent component passing in new props. | You can update it by calling setState() or forceUpdate() within the component. |
| Usage | Used to pass data from parent to child components. | They manage components’ internal state and re-render based on state changes. |
| Scope | It can be accessed throughout the component tree. | It can only be accessed within the component where it is defined. |
Q8. When to use a class component over a functional component?
Answer:
Use class components when the component needs to have state, lifecycle methods, or other advanced features such as refs. In contrast, one can use functional components for simpler components that don’t require these features and are easier to read and test. However, with the introduction of React hooks in version 16.8, functional components can now have state and lifecycle methods as well, reducing the need for class components in many cases.
Q9. How does one share the data between components in React?
Answer:
- Props: Using props is one method of transferring data from a parent component to a child component. Props are read-only, so the child component cannot alter the data passed through them.
- Context: React context offers a mechanism to share data that any component within a specific context can access. Sharing data necessary for multiple components, such as user authentication data, is most beneficial.
- Redux: Redux is a library for state management that offers a universal state store that any component can access. It enables components to dispatch actions to update the shop and subscribe to changes in the shop.
- React Query: By caching and controlling the state of asynchronous data, React Query is a data fetching module that offers a mechanism to transfer data between components. Additionally, you can use React to manage the global state.
- Local Storage: The ability to store data locally in the browser that may be accessed and shared by components is provided by local storage. We should only use local storage for modest amounts of data, not for confidential or sensitive data.
Q10. What are React hooks?
Answer: React hooks are functions that allow developers to use state and lifecycle methods in functional components.
Conclusion
Many businesses seek developers with experience in ReactJS, as it has become one of the most widely used JavaScript libraries for creating complex user interfaces. If one is preparing for the ReactJS interview, one should also prepare for JavaScript and must have practical hands-on. Preparing important concepts using interview questions can help one ace their interview.
Frequently Asked Questions (FAQs)
Q1. How do I prepare for a React interview?
Answer: To prepare for a React interview, it’s essential to review the fundamentals of React, including its core concepts, lifecycle methods, and popular tools and libraries. You should also practice building small React applications and be able to explain your approach and decision-making process. Finally, be sure to research the company you’re interviewing with and familiarize yourself with their React-related projects or initiatives.
2. How do you pass React interview questions?
Answer: To pass React interview questions, it’s essential to have a solid understanding of ReactJS’s core concepts and be able to apply them in practical scenarios. It’s also helpful to be familiar with popular React libraries and tools, such as Redux, React Router, and Jest. Practice building small React applications and be prepared to explain your thought process and decision-making. Finally, be confident, communicate clearly, and demonstrate a willingness to learn and adapt.
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