What is virtual DOM in ReactJS and how does it work?

Virtual DOM in ReactJS is a lightweight clone of the actual DOM (Document Object Model) that React uses to improve performance. When changes are made to the UI in React, the virtual DOM is updated instead of directly updating the actual DOM. This process is faster and more efficient, as React can identify only the components that have changed and then update only those parts of the actual DOM.

Here's how virtual DOM works in ReactJS:

1. When a user interacts with a React component, the state of the component changes.
2. React compares the updated virtual DOM with the previous virtual DOM to determine the changes that need to be applied to the actual DOM.
3. React then calculates the most efficient way to update the actual DOM based on the differences identified in step 2.
4. Finally, React updates the actual DOM with the changes, ensuring that only the necessary parts are re-rendered.

By using virtual DOM, React minimizes the number of DOM manipulations and re-renders, leading to faster and more optimized performance for web applications.