It looks like you added "|| !this[0].ownerDocument" - doesn't seem too bad.

I also experience this when trying to call position() (which invokes offset()) on an element within an IFrame. Please include the fix in the next version!

Ok forget I said that, it's not true that the error occurs when it's called on elements within an IFrame. My error occured because I was trying to call $(undefined).position() and $(undefined) seems to return the HTML document, which then triggers the error.

You can't run offset on window and when you run offset with no matched elements it should return null as it does now in SVN Trunk. This matches the behavior of other methods that return a result based on the first matched element (like .width()).

This function should return null. The issue is that is not happening in certain cases. Instead a javascript exception is thrown from:

$(window).offset() or $(document).offset()
TypeError: elem.ownerDocument is null

Maybe this is incorrect usage, but I feel like these calls should also return null, and not throw an error. Document and window are valid jquery object members, and don't cause errors in any other methods. Specifically, I have encountered this in my "drag" special event, I need to calculate the offset position... but I do not know if the event scope is going to be "document" or "window" and potentially break the code. I can test for document or window, but would rather have the "offset" and "position" methods test for "ownerDocument" The fix is quite simple...

Change:

if ( !elem ) return null;

To:

if ( !elem || !elem.ownerDocument ) return null;

fixed in r6319