This first command will create a new body element.
document.body = document.createElement('body');
We still have the head element with any styling that is present. You can see this by putting in some simple markup:
document.body.innerHTML = '<h1>A heading</h1><div class="BLOCKone">Block</div>';
You will probably see that the heading is styled in the way that the website you are looking at styles headings.
We can clear that out using:
document.head.innerHTML = ''
One is still left with any Javascript code which is present. Haven’t thought of an easy way to clear that yet.