1. What are higher-order components (HOCs) in React?
A higher-order component is a function that takes a component and returns a new component with enhanced functionality. HOCs are used for code reuse, such as adding lifecycle methods, modifying props, or adding additional functionality to existing components.
2. What is React Router?
React Router is a library for adding routing to a React application. It allows you to define multiple views or pages in your app and navigate between them without a full page reload.
3. What are controlled and uncontrolled components in React?
• Controlled components: Form elements where the React state is the source of truth (i.e., React controls the form element’s value).
• Uncontrolled components: Form elements where the DOM itself maintains the form element’s state, and React doesn’t directly manage it.
4. What is the Context API in React?
The Context API is a feature in React that allows you to pass data through the component tree without manually passing props to every level. It’s often used for global state management, like user authentication or theme settings.
5. What is the purpose of React.memo?
React.memo is a higher-order component that memoizes a component’s output, preventing unnecessary re-renders if the component’s props haven’t changed. It’s useful for functional components that render the same output given the same props.
6. What is Redux, and how does it relate to React?
Redux is a state management library used with React (and other libraries) to manage the global state of an application. It provides a centralized store and helps manage complex state transitions. It is often used for large applications where managing state across many components becomes cumbersome.
7. What is useEffect used for in React?
useEffect is used to perform side effects in functional components. Side effects could include data fetching, setting up subscriptions, or manually changing the DOM. It runs after the render and can optionally clean up before the component unmounts.
8. What is a key in React, and why is it important?
A key is a special string attribute that helps React identify which items have changed, are added, or are removed. It’s used in lists of elements to give each element a stable identity. This improves performance during rendering.
9. What is the virtual DOM in React?
The virtual DOM is an in-memory representation of the real DOM elements. React uses the virtual DOM to optimize the rendering process by updating only the parts of the actual DOM that need to change, instead of re-rendering the entire UI.
10. What are React hooks?
React hooks are functions that allow you to “hook into” React features (like state and lifecycle methods) from functional components. Common hooks include:
• useState: For adding state to a functional component.
• useEffect: For handling side effects (like data fetching or subscriptions).
• useContext: For accessing context values.