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.