Code Formatting (Beautify) in JavaScript

Refer below sample. Use highlight.js plugin.

HTML

<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/11.9.0/styles/default.min.css" />
<script src="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/11.9.0/highlight.min.js"></script>
<script>
    window.onload = function () {
        document.querySelectorAll('pre code').forEach(function (code) {
            hljs.highlightElement(code);
        });
    }
</script>
<div id="code-container" class="code">
    <pre>
        <code>
            function greet() { console.log('Hello, World!'); }
        </code>
    </pre>
</div>

Screenshot