<div id="parent">
    <h1>I'm parent div</h1>
</div>

<div id="child">
    <h1>I'm child div</h1>
  </div>
  
  <button id="btn">Move element</button>


<a href="https://reactgo.com" target="_blank" class="author">reactgo.com</a>

#parent{
  border:1px solid black;
  padding:1rem;
  margin:1rem;
}

#child{
  background:red;
  padding:5px;
}

.author{
  float:right;
  padding:1rem;
}

const parent = document.getElementById('parent');
const child = document.getElementById('child');
const btn = document.getElementById('btn');


btn.addEventListener('click',()=>{
  parent.appendChild(child);
})