JSFiddle - React, Tailwind, and code Playground

HTML

<div id="parent-1">
  <div id="child"></div>
</div>
<div id="parent-2"></div>

CSS

#parent-1,#parent-2 {
  height: 100px;
  width: 100px;
  background-color: grey;
  margin: 10px;
}

#child {
  height: 20px;
  width: 20px;
  background-color: black;
}

JavaScript

var parent1 = document.getElementById('parent-1'),
    parent2 = document.getElementById('parent-2'),
    child = document.getElementById('child');

parent1.appendChild(child);
console.log(child.parentNode === parent1); //true

setTimeout(function() {
  parent2.appendChild(child);
  console.log(child.parentNode === parent1); //false
}, 500);