JSFiddle - React, Tailwind, and code Playground

HTML

<div>
 <menu>
   <menuitem>text</menuitem>
   <menuitem>text2</menuitem>
 </menu>
</div>
<textarea id=output></textarea>

CSS

textarea { width: 50%; height: 400px; }

JavaScript

var m = document.querySelector('menu');
document.querySelector('#output').value = "Number of element children: " + m.childElementCount + "\n";
document.querySelector('#output').value += "Number of node children of menuitem: " + m.firstElementChild.childNodes.length + "\n";