ReactJS, a popular JavaScript library for building user interfaces, is widely used in modern web development. If you're preparing for a ReactJS interview, it's crucial to be familiar with common questions that test your understanding of core concepts, advanced techniques, and best practices. This article outlines some of the top ReactJS interview questions along with their answers.
Basic ReactJS Questions
1. What is ReactJS?
Answer: ReactJS is a JavaScript library developed by Facebook for building user interfaces, particularly single-page applications. It allows developers to create reusable UI components and manage the state of applications efficiently.
2. What are the key features of ReactJS?
Answer:
- JSX: A syntax extension that allows HTML to be written within JavaScript.
- Virtual DOM: Improves performance by updating only the changed parts of the real DOM.
- Components: Building blocks of a React application that manage their own state and render UI.
- One-way Data Binding: Ensures data flows in one direction, making debugging easier.
- Lifecycle Methods: Allow developers to hook into different stages of a component's lifecycle.
3. Explain the concept of Virtual DOM.
Answer: The Virtual DOM is a lightweight copy of the actual DOM. React uses the Virtual DOM to perform efficient updates by comparing the virtual representation with the real DOM and updating only the parts that have changed. This improves performance and efficiency.
4. What is JSX?
Answer: JSX (JavaScript XML) is a syntax extension for JavaScript that resembles HTML. It allows developers to write HTML-like code within JavaScript. JSX is transpiled to JavaScript by tools like Babel.
5. What are React components?
Answer: React components are the building blocks of a React application. They are reusable, self-contained pieces of code that render part of the user interface. Components can be class-based or functional.
Intermediate ReactJS Questions
6. What is the difference between state and props?
Answer:
- State: Managed within a component and can be changed. It represents the dynamic data of the component.
- Props: Passed from parent to child components and are immutable. They are used to pass data and event handlers to child components.
7. What are lifecycle methods in React?
Answer: Lifecycle methods are hooks that allow developers to run code at specific points in a component's lifecycle. Examples include:
- componentDidMount: Runs after the component is mounted.
- componentDidUpdate: Runs after the component updates.
- componentWillUnmount: Runs before the component is unmounted and destroyed.
8. What is Redux?
Answer: Redux is a state management library for JavaScript applications. It provides a centralized store for the application state, enabling predictable state transitions and easier debugging. Redux works well with React through the react-redux binding.
9. What is a higher-order component (HOC)?
Answer: A higher-order component is a function that takes a component and returns a new component with additional props or behavior. HOCs are used for code reuse, logic abstraction, and managing cross-cutting concerns.
10. What are hooks in React?
Answer: Hooks are functions that let you use state and other React features in functional components. Common hooks include:
- useState: Manages state in functional components.
- useEffect: Performs side effects in functional components.
- useContext: Consumes context in functional components.
Advanced ReactJS Questions
11. What is the Context API?
Answer: The Context API provides a way to pass data through the component tree without having to pass props down manually at every level. It is used for managing global state or passing data deeply into the component tree.
12. Explain the concept of code splitting in React.
Answer: Code splitting is a technique to split your code into smaller bundles that can be loaded on demand. This improves the performance of large applications by reducing the initial load time. React supports code splitting with dynamic import() and React.lazy.
13. What is React Fiber?
Answer: React Fiber is the new reconciliation algorithm in React 16 and above. It improves the rendering process by breaking down rendering work into units and allowing React to prioritize and pause work. This makes updates more efficient and responsive.
14. How do you handle forms in React?
Answer: Forms in React can be handled using controlled components, where form data is handled by the component's state. The form elements have value and onChange attributes to synchronize the state with the input value.
15. What is React.memo?
Answer: React.memo is a higher-order component that prevents functional components from re-rendering if their props have not changed. It is used to optimize performance by reducing unnecessary renders.
source : Top ReactJS interview questions and answers