onclick focus cursor after the text in the textarea box

[coding_begins]

hi I was working on comments module where i pull of the usernames and insert them into a text area when i click a button.
Now I want the cursor to point to the end of the username everytime i click the button. I tried using the focus() property but it takes me to the beginning of the text area.
here is my code so far:

<script type="text/javascript">
	function setComments(userID) {
	    document.getElementById("comments_content").value = document.getElementById("comments_content").value + userID + "\n\n";
	}
</script>

<a onclick="setComments('<?php print $comment_username; ?>') + document.edit.comments_content.focus()" href="#addcomment">
   <img src="images/reply-button.png" align="top" border="0">
</a>

<textarea class='comment-input-textarea-loggedin'  id='comments_content' name='comments_content'></textarea>

[desiter]

See this topic: http://www.codingforum.net/showthread.php?t=235907