First of all – the Virtual DOM was not invented by React, but React uses it and provides it for free.
The Virtual DOM is an abstraction of the HTML DOM. It is lightweight and detached from the browser-specific implementation details. Since the DOM itself was already an abstraction, the virtual DOM is, in fact, an abstraction of an abstraction
Shadow DOM creates small pieces of the DOM object which has their own, isolated scope for the element they represent.
The Diffing Algorithm
When diffing two trees, React first compares the two root elements. The behavior is different depending on the types of the root elements.,