JSFiddle - React, Tailwind, and code Playground

HTML

<div id="old-parent">
    <span>Foo</span>
    <b>Bar</b>
    Hello World
</div>
<div id="new-parent"></div>

JavaScript

function setParent(el, newParent)
{
    newParent.appendChild(el);
}

var l = document.getElementById('old-parent').childNodes.length;
var a = document.getElementById('old-parent');
var b = document.getElementById('new-parent');
for (var i = l; i >= 0; i--)
{
    setParent(a.childNodes[0], b);
}