JSFiddle - React, Tailwind, and code Playground

HTML

<div id="test">This test DIV contains some text.</div>

JavaScript

var observer = new MutationObserver(function (m) {
        console.log(m);
    }),
    elem = document.getElementById('test');

observer.observe(elem, {childList: true});
setTimeout(function () {
    elem.textContent += ' This is an added part triggering Mutation Observer.';
}, 2000);