The Virtual DOM in React JS is an in-memory representation of the actual Document Object Model (DOM) that exists in the browser. The virtual DOM is a lightweight, abstract representation of the actual DOM that can be manipulated by React without directly affecting the browser DOM, which can be expensive in terms of performance.
When a React component is rendered, it creates a virtual DOM tree that mirrors the structure of the actual DOM tree. Each element in the virtual DOM is represented by a JavaScript object that contains information about the element’s type, properties, and children.
The virtual DOM is used to compare the previous and current states of a component and determine the minimum set of changes needed to update the actual DOM. This process is known as reconciliation, and it involves comparing the old virtual DOM tree with the new virtual DOM tree and calculating the differences between them.
Once the differences have been calculated, React updates the browser DOM with only the changes that are needed, minimizing the number of updates required and improving performance.
The virtual DOM is created by React in memory using JavaScript objects. The virtual DOM is built by React from the React components and their corresponding JSX elements. Each time a component renders, React creates a new virtual DOM tree and compares it with the previous virtual DOM tree to determine the changes that need to be made to the actual DOM.
In summary, the Virtual DOM in React JS is an in-memory representation of the actual DOM that is created by React. It is a lightweight, abstract representation that is used to determine the minimum set of changes needed to update the actual DOM, improving performance and minimizing updates. The Virtual DOM is created in memory by React using JavaScript objects.