Why is ReactDOM.render() not rendering

I am trying to create a webpage with React however when I use ReactDOM.render(), it fails to render the element.Here is my HTML :

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <meta http-equiv="X-UA-Compatible" content="IE=edge">
        <title></title>
        <meta name="description" content="">
        <meta name="viewport" content="width=device-width, initial-scale=1">

    </head>
    <body>
        <div id="root"> </div>
        <script src="https://unpkg.com/react@17/umd/react.development.js" crossorigin></script>
        <script src="https://unpkg.com/react-dom@17/umd/react-dom.development.js" crossorigin></script>
        <script src ="ReactTest.js" type="text/babel">
        </script>
    </body>
</html>

Now here is my JavaScript code:

ReactDOM.render(
     <h1> Hello 1</h1>,
     document.getElementById("root")
)

Why does it fail to render?