Preparing for a ReactJS interview as a beginner can be daunting, but having the right set of questions and answers can significantly boost your confidence. In this blog post, we will cover the top 25 ReactJS interview questions, along with their answers, explanations, and tips on how to effectively frame your responses. For more detailed interview preparation, visit PrepVerse.

What is React.js, and why is it so popular?

Answer: React.js is an open-source JavaScript library developed by Facebook for building user interfaces, particularly for single-page applications. It’s popular because of its component-based architecture, virtual DOM for efficient updates, and a strong ecosystem of tools and libraries.
How to Frame: Highlight its key features like reusability, performance, and ease of learning. Mention its use in popular apps like Facebook, Instagram, and Netflix.

What are the key features of React?

Answer: Key features include:
- Virtual DOM: Improves performance by minimizing direct DOM manipulation.
- Component-Based Architecture: Encourages reusability and modularity.
- JSX: Allows writing HTML-like syntax in JavaScript.
- Unidirectional Data Flow: Ensures predictable state management.
How to Frame: Use examples to explain how these features benefit developers.

What is JSX?

Answer: JSX (JavaScript XML) is a syntax extension that allows you to write HTML-like code in JavaScript. It makes the code more readable and easier to write.
How to Frame: Explain how JSX gets transpiled into React.createElement() calls.

What are components in React?

Answer: Components are the building blocks of a React application. They are reusable and independent pieces of code that return HTML (via JSX) to render on the UI.
How to Frame: Differentiate between functional components and class components.

What is the difference between functional and class components?

Answer:
- Functional Components: Stateless, simpler, and use hooks for state management.
- Class Components: Stateful, use lifecycle methods, and are more complex.
How to Frame: Mention that functional components are now preferred due to hooks.

What are props in React?

Answer: Props (short for properties) are used to pass data from a parent component to a child component. They are read-only.
How to Frame: Use an example to demonstrate how props work.

What is state in React?

Answer: State is a built-in React object used to store data or information about the component. It is mutable and can be updated using setState() (in class components) or useState() hook (in functional components).
How to Frame: Explain how state triggers re-renders.

What are React hooks?

Answer: Hooks are functions that let you use state and other React features in functional components. Examples include useState, useEffect, and useContext.
How to Frame: Highlight how hooks simplify code compared to class components.

Explain the useState hook.

Answer: useState is a hook that allows you to add state to functional components. It returns an array with the current state value and a function to update it.
How to Frame: Provide a simple counter example.

What is the useEffect hook?

Answer: useEffect is used to perform side effects in functional components, such as fetching data or updating the DOM. It runs after every render.
How to Frame: Explain dependency arrays and cleanup functions.

What is the Virtual DOM?

Answer: The Virtual DOM is a lightweight copy of the real DOM. React uses it to optimize updates and improve performance by minimizing direct DOM manipulation.
How to Frame: Compare it to the real DOM and explain the diffing algorithm.

What are keys in React?

Answer: Keys are unique identifiers used to help React identify which items have changed, been added, or been removed in a list.
How to Frame: Emphasize their importance in list rendering.

What is React Router?

Answer: React Router is a library used for routing in React applications. It enables navigation between different components without reloading the page.
How to Frame: Mention BrowserRouter, Route, and Link.

What is Redux, and why is it used?

Answer: Redux is a state management library for JavaScript apps. It helps manage global state in a predictable way.
How to Frame: Explain actions, reducers, and the store.

What are higher-order components (HOCs)?

Answer: HOCs are functions that take a component and return a new component with additional props or functionality.
How to Frame: Provide an example, such as adding authentication.

What is context in React?

Answer: Context provides a way to pass data through the component tree without manually passing props at every level.
How to Frame: Compare it to prop drilling.

What are controlled and uncontrolled components?

Answer:
- Controlled Components: Form data is handled by React state.
- Uncontrolled Components: Form data is handled by the DOM itself.
How to Frame: Use examples like input fields.

What is prop drilling?

Answer: Prop drilling is the process of passing props through multiple levels of components, which can become cumbersome.
How to Frame: Suggest solutions like Context API or Redux.

What are React fragments?

Answer: Fragments let you group a list of children without adding extra nodes to the DOM.
How to Frame: Use <React.Fragment> or <> </> syntax.

What is the significance of `setState`?

Answer: setState is used to update the state in class components and triggers a re-render of the component.
How to Frame: Explain asynchronous behavior and batching.

What is the difference between `element` and `component`?

Answer:
- Element: A plain object describing what you want to appear on the screen.
- Component: A function or class that returns an element.
How to Frame: Use examples to clarify.

What is the purpose of refs in React?

Answer: Refs provide a way to access DOM nodes or React elements directly.
How to Frame: Use cases like focusing an input field.

What is the difference between `useCallback` and `useMemo`?

Answer:
- useCallback: Returns a memoized callback function.
- useMemo: Returns a memoized value.
How to Frame: Explain performance optimization.

What is error boundary in React?

Answer: Error boundaries are components that catch JavaScript errors anywhere in their child component tree.
How to Frame: Mention componentDidCatch lifecycle method.

How do you optimize performance in React?

Answer: Techniques include using React.memo, useMemo, useCallback, lazy loading, and code splitting.
How to Frame: Provide real-world examples.

Final Tips for Framing Answers:

Be Concise: Avoid overloading your answer with unnecessary details.
Use Examples: Practical examples make your answers more relatable.
Show Confidence: Even if you’re unsure, explain your thought process.
Link to Resources: Mention tools like PrepVerse for further learning.

Conclusion

Preparing for a React.js interview doesn’t have to be stressful. By mastering these top 25 React.js interview questions, you’ll be well-equipped to showcase your skills and land your dream job. For more in-depth tutorials and practice questions, visit PrepVerse, your go-to resource for coding interview preparation.

Good luck with your interview preparation! 🤞

Ace Your ReactJS Interviews

Ace Your ReactJS Interviews