JSFiddle - React, Tailwind, and code Playground

HTML

<div id="testdiv" style="display:none;">hidden</div>
<button id="show">Show hidden div</button>

JavaScript

$(function () {
    $('#show').click(function () {
        $('#testdiv').show();
    });

    var observer = new MutationObserver(function (mutations) {
        console.log("foo")
    });
    var target = document.querySelector('#testdiv');
    observer.observe(target, {
        attributes: true
    });

});