Iair, so what you are saying is that you want to know if, at any point in time, there are any page elements that are still loading? for example, if a mouse click appends a script to the page you need to know if the script has loaded or not?
If that's the case, then I've been also trying to get this functionality as well, but with no great results. In the case of scripts in particular what I've done is set up a timer that checks for a specific function contained in that script. If the function exists, it meas the script has loaded; otherwise the script is still loading (or the function does not exist, or the path of the script is incorrect). Perhaps a timer that checks if an element exists ($ (selector).length>0) should do the trick for all types of files (scripts,styles, imgs etc)?
