How to dispose of DOM elements in JavaScript to avoid memory leaks

Question

I have an application that allows a user to view details on a specific case w/out a postback. Each time a user requests data from the server I pull down the following markup.

<form name="frmAJAX" method="post" action="Default.aspx?id=123456" id="frmAJAX">
<div>
<input type="hidden" name="__VIEWSTATE" id="__VIEWSTATE" />
</div>
<div>
<input type="hidden" name="__EVENTVALIDATION" id="__EVENTVALIDATION" />
</div>
<div id="inner">
<!-- valid info here --!>
</div>
</form>

Next I take the above and innerHTML it to a new DOM element like so:

   success: function(xhtml) {
        var tr = document.createElement('tr');
        var td = document.createElement('td');
        var container = document.createElement('div');

        obj.parentNode.parentNode.parentNode.insertBefore(tr, obj.parentNode.parentNode.nextSibling);

        td.appendChild(container);
        container.innerHTML = xhtml;
        tr.appendChild(td);

but after the above, I use some jQuery to remove the nasty aspnet junk

$('form:eq(1)').children().each(
    function() {
        if ($('form:eq(1)').find('div').filter(function() { return $(this).attr('id') == ''; }).remove());
    }
);

//Capture the remaining children
var children = $('form:eq(1)').children();

// Remove the form
$('form:eq(1)').remove();

// append the correct child element back to the DOM
parentObj.append(children);

My question is this - When using IESieve I notice no actual leaks but an ever growing number of DOM elements (thus memory usage).

What can I improve on in the client-side to actually cleanup this mess? Note- both IE7/8 show these results.

EDIT: I did finally get this working and decided to write a short blog post with complete source code.

Answer 1

remove() and its ilk only remove elements from the DOM. They still exist in memory somewhere.

This is a known problem with AJAX and Web 2.0. There's little you can do aside from designing your site to ensuring that you occasionally have a page refresh to wipe things away.

Answer 2

The tricky part is figuring out where a reference still exists to the offending nodes.

You're doing this the hard way — you're adding all the markup to the page, then removing the stuff you don't want. I'd do it this way instead:

var div = document.createElement('div');
// (Don't append it to the document.)

$(div).html(xhtml);

var stuffToKeep = $(div).find("form:eq(1)> *").filter(
  function() {
    return $(this).attr('id') !== '';
  }
);

parentObj.append(stuffToKeep);

// Then null out the original reference to the DIV to be safe.
div = null;

This isn't guaranteed to stop the leak, but it's a good start.