JSX is a syntax extension to JavaScript. It is similar to a template language, but it has full power of JavaScript. JSX gets compiled to React.createElement() calls which return plain JavaScript objects called “React elements”. To get a basic introduction to JSX see the docs here and find a more in-depth tutorial on JSX here.
React DOM uses camelCase property naming convention instead of HTML attribute names. For example, tabindex becomes tabIndex in JSX. The attribute class is also written as className since class is a reserved word in JavaScript:
const name = 'Clementine';
ReactDOM.render(
<h1 className="hello">My name is {name}!</h1>,
document.getElementById('root')
);