How to access DOM elements when the ids were dynamically created with numbers

I am building a forum page that submits a number of comments with respect to a subject much like the one we are on. Hence, when I acess the database to display the comments, I need to dynamically create the id of some div's of my content, something like this:

 while($row=mysql_fetch_assoc($result))
 {
 ?>
  <div id="post<?=$row["postId"] ?>" class="seeForumPost"><?=$row["post"] ?> </div>  //this one 
   <div id="postFooter<?=$row["postId"] ?>" class="seeForumPostFooter"> //this one
     <div class="byUser">  
       by <a class="commonLink" href="<?php print "seeUser.php?userId=".$row['userId'] ?>"> <strong><?=ucwords($row["firstname"]) ?> <?=ucwords($row["lastname"]) ?></strong></a>
 </div>
     <div class="likeThisForum"> Like this Post</div> 
     <div class="numberOfLikes"&开发者_运维问答gt; (<?=$row["postLikes"] ?> likes) </div>
     <div id="<?=$row["postId"] ?>" onclick="reportPostSpam()" class="markAsSpam">Mark as spam</div>   //this one
  </div>
 <?php } ?>

Thats right. I am using numbers inside my id, so they appears like "post26" "postFooter26" and "26" But I don't know how to fetch these DOM objects in my ajax request (prototype). I cant't seem to deal with those parentNode and previousSiblings properties because then the javascript method throws cannot call property style of undefined. Helps are appreciated.

You can always try:

<div id="<?=$row["postId"] ?>" onclick="reportPostSpam(<?=$row["postId"] ?>)" class="markAsSpam">Mark as spam</div>

Would be much simplier