Untitled

<!DOCTYPE HTML>
<html lang="ru">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
</head>
<body>
<div> This is a paragraph1.
  <div>This is a paragraph2.
    <p>This is a paragraph3.</p>
    <p>This is a paragraph4.</p>
  </div>
  <div>This is a paragraph5.</div>
</div>
<div id="el1">
</div>
<script type="text/javascript">
function printTag(tag, offset) {
  if (tag.tagName == undefined) {
      return;
  }

  var tg = document.createElement("p");
  tg.style.paddingLeft = offset*20;
  tg.innerHTML = tag.tagName;
  elem.appendChild(tg);

  if (!(tag.children == undefined)) {
      for (var i = 0, len = tag.children.length; i < len; i++) {
          if (tag.children[i].tagName != undefined) {
              printTag(tag.children[i], offset+1);
          }
      }
  }
}

var elem = document.getElementById("el1");
printTag(document.documentElement, 0)
</script>
</body>
</html>