or in react js code example

Example 1: what is react

This is a formatted version of Komadori's answer 
(https://tinyurl.com/Komadori)
React is a JavaScript library for building user interfaces. 
It is maintained by Facebook and a community of 
individual developers and companies. 
React can be used as a base in the development of single-page 
or mobile applications.

Example 2: javascript in jsx

const name = 'Josh Perez';
const element = <h1>Hello, {name}</h1>;
//notice the use of {...} to jump from jsx to javascript.
ReactDOM.render(
  element,
  document.getElementById('root')
);