JSFiddle - React, Tailwind, and code Playground

HTML

<!doctype html>
<html>
<head>
 <meta charset="utf-8">
</head>
<body>
 <!-- HTML elements will be here -->
 <script src="./source.js"></script>
</body>
</html>
<body>
    <!-- HTML elements will be here -->
    <h1 id="myHeader">Headline</h1>
</body>

JavaScript

let header = document.getElementById('myHeader');
header.innerHTML = 'Hello world';