React Interview Questions

Sure! Here are some common React interview questions along with brief answers:

1. What is React? React is a JavaScript library for building user interfaces. It allows developers to create reusable UI components and efficiently update and render them when the data changes, using a virtual DOM.

2. What is JSX? JSX (JavaScript XML) is a syntax extension for JavaScript used in React. It allows you to write HTML-like code within JavaScript, making it easier to describe the structure and appearance of components.

3. What is the difference between functional components and class components in React? Functional components are JavaScript functions that return JSX elements and do not have their own internal state. Class components, on the other hand, are JavaScript classes that extend the React.Component class and can have their own state and lifecycle methods.

4. What are React hooks? Hooks are functions introduced in React 16.8 that allow you to use state and other React features in functional components. They provide a way to reuse stateful logic without writing class components.

5. What is the significance of the "key" prop in React? The "key" prop is used to give a unique identifier to each element in an array rendered by React. It helps React efficiently update the DOM by determining which elements have changed, been added, or been removed.

6. Explain the concept of virtual DOM in React. The virtual DOM is a lightweight copy of the actual DOM maintained by React. When the state of a component changes, React compares the virtual DOM with the previous version and computes the minimal set of changes needed to update the actual DOM. This approach improves performance by minimizing direct manipulation of the real DOM.

7. What are controlled components in React? Controlled components are React components whose values are controlled by React itself. The component receives its current value and updates its value through props, and the value is typically stored in the component's state. This allows React to have full control over the component's behavior.

8. What are React lifecycle methods? React lifecycle methods are special methods that are called at specific stages of a component's life, such as when it is being mounted, updated, or unmounted. Some commonly used lifecycle methods are componentDidMount, componentDidUpdate, and componentWillUnmount.

9. What is the purpose of using keys in lists? Keys are used in lists to help React identify which items have changed, been added, or been removed. They help optimize the rendering process by minimizing DOM updates. Keys should be unique among siblings but can be shared across different components.

10. How can you optimize the performance of a React application? Performance optimization in React can be achieved by using techniques such as:

• Memoization and useMemo for caching expensive calculations.
• Using React.PureComponent or implementing shouldComponentUpdate to avoid unnecessary re-rendering.
• Code splitting and lazy loading for loading components on demand.
• Implementing shouldComponentUpdate or using React.memo to prevent unnecessary re-rendering of child components.

These are just a few examples of React interview questions. It's always a good idea to study and understand the concepts thoroughly and be prepared to discuss your practical experience with React projects.