AFAIK top window frameElement returns null and not undefined, as is for document.body when not present yet.
Moreover we can use the JavaScript weird case where null == undefined but while null is static, undefined can be redefined or in any case it needs to be discovered in the scope chain. On line 857 of this event.js http://github.com/jquery/jquery/blob/master/src/event.js I can spot this: toplevel = window.frameElement === undefined; In few words and at least in my IE8 that doScroll try/catch is never performed at all since the condition if( document.documentElement.doScroll && toplevel) cannot be true. Is that file part of the release? I did not check but you can quickly fix via toplevel = window.frameElement == null; Regards -- You received this message because you are subscribed to the Google Groups "jQuery Development" group. To post to this group, send email to jquery-...@googlegroups.com. To unsubscribe from this group, send email to jquery-dev+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/jquery-dev?hl=.