No more hacks for the MS AJAX’s binding problem

At least, when the RTM version is released!

Ok, I guess you need some context: in the previous post, I talked about a problem which was mentioned to me by Andy in the comments of an existing post. The problem was that the __msajaxBindings field ended up being added to an object used in a live binding and that really means trouble when you try to serialize it (because you end up with a cyclic reference which generates a runtime exception).

In the previous post, I suggested a hack for it. Fortunately, Dave saw it and emailed me assuring that the hack won’t be necessary and that the internal __msajax… fields should only be added to HTML elements. As you’re probably expecting by now, the problem I mentioned in the previous post is the result of a bug (which will be solved before the RTM is out).

After being alerted by Dave, I’ve decided to take a closer look at the code…And yes, there’s a problem and it’s on the Sys.UI.DomElement.isDomElement method. This method ends up invoking the _isDomElement method which has a check that returns a “false positive”:

Sys._isDomElement = function Sys$_isDomElement(obj) {
   var val = false;
   if (typeof (obj.nodeType) !== ''number'') {
     var doc = obj.ownerDocument || obj.document || obj;
     if (doc != obj) {
       var w = doc.defaultView || doc.parentWindow;
       val = (w != obj);
     else {
       val = (typeof (doc.body) === ''undefined'');
  return !val;

Can you spot the problem? Yep, the val = (typeof(doc.body)… line is responsible for considering the object a DOM element (remember: section had a property called body and if you look at the code, you’ll see that it ends up messing everything). While the good guys at MS don’t publish a new release which solves this bug, you really shouldn’t use any property named body in an object which is used in a binding relationship (at least,if you intend to serialize that object). Ok,to be fair, you can always use the previous awful hack, but If I were you, I’d renamed the property 🙂

And that’s it for now. Stay tuned for more.


~ by Luis Abreu on November 13, 2009.

2 Responses to “No more hacks for the MS AJAX’s binding problem”

  1. Brill. Thank you. All my “body” properties will from now on be renamed “bodyText”!

  2. Thank Dave…he”s the one that spotted the problem 🙂

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