Virtual DOM

The [[Document Object Model (DOM)]] is a programming interface for HTML.
It represents the page so that programs can change the structure, style and content.
The DOM is an object orientated representation of the HTML page.
The Virtual DOM is an of the HTML DOM.
It is a node tree that represents elements as objects and their attributes as properties.
It is React's local copy of the HTML DOM.
The Virtual DOM was not invented by React, React just uses it.

You need to replace the HTML 'class' attribute name to 'className' inside the render method because class is a reserved word in JavaScript.