Untitled

<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8" />
    <title>Hello World</title>
    <script src="https://unpkg.com/react@16/umd/react.development.js"></script>
    <script src="https://unpkg.com/react-dom@16/umd/react-dom.development.js"></script>
    <script src="https://unpkg.com/babel-standalone@6.15.0/babel.min.js"></script>
</head>
<body>
    <div id="root"></div>
    <script type="text/babel">

        ReactDOM.render(
        <h1>Hello, world!</h1>,
        document.getElementById('root')
        );

    </script>
</body>
</html>

<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8" />
    <title>Hello World</title>
    <script src="https://unpkg.com/react@16/umd/react.development.js"></script>
    <script src="https://unpkg.com/react-dom@16/umd/react-dom.development.js"></script>
    <script src="https://unpkg.com/babel-standalone@6.15.0/babel.min.js"></script>
    <script src="Scripts/custom/react.js"></script>
</head>
<body>
    <div id="root"></div>
</body>
</html>

ReactDOM.render(
    <h1>Hello, world!</h1>,
    document.getElementById('root')
);