JSFiddle - React, Tailwind, and code Playground

HTML

<div id="boxA" style="border:1px solid red;">
  <ul tabindex="1">
    <li>x</li>
    <li>y</li>
    <li>z</li>
  </ul>
</div>
<div id="boxB">
<ul tabindex="2">
    <li>x</li>
    <li>y</li>
    <li>z</li>
  </ul>
</div>

JavaScript

$('#boxA, #boxA > *').focusout(function () {
    if ($(document.activeElement).closest('#boxA').length == 0){
        alert("not focussed");
    }
});