textContent includes script

.textContent includes source of descendant script nodes

HTML

<div>Source: <span id="source">
<!-- html comment -->
<script><!-- //script here --></script>
Text
</span>
</div>
<div>Dest: <span id="dest"></span></div>

JavaScript

var sourceEl = document.getElementById('source');
var destEl = document.getElementById('dest');
destEl.textContent = sourceEl.textContent;
destEl.textContent = "Coucou";