React is an open-source Javascript library for building single-page web applications with declarative code. It allows us to create reusable UI components which comes very handy while building large applications where the same UI kits are used multiple times. React maintains a virtual DOM tree. That tree is used for effectively re-construct HTML DOM through Javascript and to push only the changes to the DOM which have actually occurred. In the process, JSX is a syntactic sugar used for creating specific Javascript objects.
First JSX syntax is parsed into javascript object.
Then react renders the javascript object with ReactDOM and recursively creates nodes based on their 'type' property and finally appends them to the DOM.