Puzzling javascript array behavior

Question

So, this may be a really stupid question, but I'm obviously missing something here.

Consider the following code:

    var selectedItems = [];
    selectedItems.push("0ce49e98-a8aa-46ad-bc25-3a49d475e9d3");
    //fyi, selectedItems[selectedItems.length] = "0ce49e98-a8aa-46ad-bc25-3a49d475e9d3"; produced the same result.

At the end selectedItems content looks like this:

Name              Value                                    Type
-------------     --------------------------------------   ------
selectedItems     {...}                                    Object
   -  [0]         "0ce49e98-a8aa-46ad-bc25-3a49d475e9d3"   String
   -  length      1                                        Long

But if I just try to call split() on the same string, like this:

selectedItems = "0ce49e98-a8aa-46ad-bc25-3a49d475e9d3".split(",")

Now the content of my supposed array looks like this (missing length):

Name              Value                                    Type
-------------     --------------------------------------   ------
selectedItems     {...}                                    Object
   -  [0]         "0ce49e98-a8aa-46ad-bc25-3a49d475e9d3"   String

Any idea what the difference is? What's actually happening here?
Thanks in advance.

UPDATED: I have a feeling there's actually something structurally different about the two resulting values, because (atlas) ajax chokes on the one with the length property when I try to pass it to a server-side WebMethod (no actual error message, but I know the call fails). I'm not sure.

UPDATE #2 I noticed that setting the targetLocationIdList this way, results in no 'length' property being displayed in Quick Watch window:

  var params = 
  {
    jobId : args.get_JobId(), 
    targetLocationIdList : retVal.split(',')
  };

But this results contain 'length' property displayed in Quick Watch window:

  var retValArr = [];
  retValArr = retVal.split(',');

  var params = 
  {
    jobId : args.get_JobId(), 
    targetLocationIdList : retValArr 
  };

Answer 1

There isn't a difference at all programmatically. If you run your example in both chrome developers window and firebug it looks like the 2nd

 Name              Value               
 Type
 -------------     --------------------------------------   ------ 
 selectedItems     {...}                                    Object
    -  [0]         "0ce49e98-a8aa-46ad-bc25-3a49d475e9d3"   String

Length is an implied property

EDIT

var retVal = 'test';
var params = 
  {
    jobId : 1, 
    targetLocationIdList : retVal.split(',')
  }; 
console.log(params.targetLocationIdList.length) // prints 1

The code above prints 1 in IE8,Firefox,Chrome (in their dev tools or firebug) so think that this must be an issue with Visual Studio or with Atlas in the way that it shows the object.

Answer 2

Might this be a bug in the debugger? (Or is this causing problems in the browser?)