React JS is one of the most popular JavaScript libraries for building user interfaces, and with its widespread usage, it’s no surprise that it’s a common topic in technical interviews. If you’re preparing for a React JS interview, it’s essential to be familiar with a variety of questions that can be asked. In this article, we will explore some of the most frequently asked React JS interview questions to help you ace your interview.
1. What is React JS?
This is a fundamental question that every interviewee should be able to answer. React JS is an open-source JavaScript library created by Facebook for building user interfaces, primarily for single-page applications. It allows developers to create reusable UI components and efficiently update and render components when the underlying data changes.
2. Explain the difference between React and React Native.
While both React and React Native are developed by Facebook, they serve different purposes. React is used for building web applications, while React Native is a framework for building native mobile applications using JavaScript and React. The main difference lies in the way they render UI components and interact with the native platform.
3. What is JSX, and how is it different from HTML?
JSX is a syntax extension for JavaScript that looks similar to HTML. It allows developers to write UI components using a syntax that is easy to read and understand. The main difference between JSX and HTML is that JSX is processed by the React compiler and transformed into JavaScript objects before being rendered.
4. What are the key differences between class components and functional components?
Class components and functional components are two ways to create React components. Class components are created using ES6 classes and can use lifecycle methods like `componentDidMount`, `componentDidUpdate`, and `componentWillUnmount`. Functional components, on the other hand, are simpler and more concise. They don’t have lifecycle methods and are stateless by default.
5. Explain the concept of props in React.
Props, short for “properties,” are the way to pass data from parent to child components. They are passed as arguments to the component and can be accessed using the `this.props` syntax in class components or the `props` object in functional components. Props are used to control the behavior and appearance of child components based on the data provided by their parent components.
6. What is the purpose of the `key` prop in React?
The `key` prop is used to provide a unique identifier for each child element in a list or array. It helps React identify which items have changed, are added, or are removed, and it’s crucial for optimizing the rendering performance of lists.
7. Explain the difference between state and props.
State and props are both ways to pass data to components, but they serve different purposes. State is an object that holds the data that changes over time and is managed by the component itself. Props, on the other hand, are read-only and passed from parent to child components.
8. What are the advantages of using React Hooks?
React Hooks are a feature introduced in React 16.8 that allow you to use state and other React features without writing a class. They make it easier to write functional components and improve code readability and maintainability.
9. What is the purpose of the `context` API in React?
The context API is a way to pass data through the component tree without having to pass props down manually at every level. It allows you to create a global state that can be accessed by any component in the application, making it easier to manage and share data across different components.
10. What are the most common performance optimizations in React?
Performance optimizations in React are crucial for building scalable and efficient applications. Some common optimizations include using the `shouldComponentUpdate` lifecycle method, using the `React.memo` higher-order component, avoiding unnecessary renders, and using the `useCallback` and `useMemo` hooks.
By familiarizing yourself with these React JS interview questions and their answers, you’ll be well-prepared to showcase your knowledge and skills during your interview. Good luck!
