You can notice the iframe reloads when ever ever change parents is clicked.
document.getElementById('changeParent').addEventListener('click',
() => {
document.getElementById('container2')
.append(
document.querySelector('iframe')
);
});
<div id="container1">
<iframe src='https://developer.mozilla.org/en-US/'></iframe>
</div>
<div id="container2">
</div>
<button id='changeParent'> Change Parents</button>