This example shows how to use the mml-chtml component to process a complete HTML page containing MathML notation into math using the CommonHTML format.
The key line is
<script id="MathJax-script" async src="https://cdn.jsdelivr.net/npm/mathjax@3/es5/mml-chtml.js"></script>
which loads the mml-chtml component. The rest is handled by MathJax automatically.