index-01d

HTML

<!DOCTYPE html>
<html lang="en">

  <head>
    <meta charset="UTF-8">
    <title>React</title>
  </head>

  <body>
    <div id="root"></div>
    <script src='//unpkg.com/react/umd/react.development.js'></script>
    <script src='//unpkg.com/react-dom/umd/react-dom.development.js'></script>
    <script src="//unpkg.com/babel-standalone@6.15.0/babel.min.js"></script>
  </body>

</html>

Babel + JSX

function formatName(user) {
    return user.firstName + ' ' + user.lastName;
}

const user = {
    firstName: 'Harper',
    lastName: 'Perez'
};

const element = (
    <h1>
        Hello, {formatName(user)}!
    </h1>
);

ReactDOM.render(
    element,
    document.getElementById('root')
);