JSFiddle - React, Tailwind, and code Playground

HTML

<h2>Lorem</h2>
<p>Please note browser console... :)</p>

<button>Fake DOM change</button>

JavaScript

var observer = new MutationObserver(function(mutations) {
  document.contains(document.querySelector('h2')) ?
    console.log("It's in the DOM!") :
    console.log("It's not in the DOM!");
});

observer.observe(document.body, {
  attributes: false,
  childList: true,
  characterData: false,
  subtree: true
});

var btn = document.querySelector('button');
btn.addEventListener('click', function() {
  var ele = document.querySelector('h2');

  if (document.contains(ele)) {
    ele.remove();
  } else {
    makeNode();
  }
});

function makeNode() {
  var headline = document.createElement('h2');
  headline.innerText = 'Lorem';
  document.body.insertAdjacentElement('afterbegin', headline);
}