Организуем древовидные комментарии к статьям c помощью JavaScript

function $(id) { return document.getElementById(id); }
      
function $attr(x, y) {
  var attr = (x.attributes) ? x.attributes[y] : null;
  return (attr) ? attr.value : null;
}
      
var comments = $("comments").getElementsByTagName("div");
for (var i = 0; i < comments.length; i++) {
  var x = comments[i];
  if ($attr(x, "class") != "comment") continue;
    
  var parentId = $attr(x, "parentId");
  if (!parentId) continue;
    
  $(parentId).appendChild(x);
}

* This source code was highlighted with Source Code Highlighter.

<div name="comments" id="comments">
  <div class="comment" id="comment1">Comment 1</div>
  <div class="comment" id="comment2" parentId="comment1">Comment 2</div>
  <div class="comment" id="comment3" parentId="comment1">Comment 3</div>
  <div class="comment" id="comment4" parentId="comment2">Comment 4</div>
  ...
</div>

* This source code was highlighted with Source Code Highlighter.