React is a JavaScript library developed by Facebook for building user interfaces using reusable components and a virtual DOM for efficient rendering.

What are React hooks?

Hooks are functions that allow you to use state and lifecycle features in functional components. Common hooks include useState, useEffect, useContext, and useReducer.

What is the virtual DOM?

The virtual DOM is an in-memory representation of the real DOM. React uses it to determine what changes need to be made and updates only those parts in the actual DOM efficiently.

React.js Interview Questions

61. What causes unnecessary re-renders in React?

62. How would you optimize React rendering performance?

63. What is reconciliation complexity in React?

64. How does React handle DOM updates efficiently?

65. What is lifting state up?

66. What are derived states and why can they be problematic?

67. What are error boundaries in React?

68. What types of errors can error boundaries catch?

69. What are React lifecycle methods?

70. How do lifecycle methods map to hooks?