[Ajax] Non riesco a verificare lo stato

[keratox]

                function takeResponse(url){
                        if(req.status==200)
                                location.href=url;                                     
                }

Risultato:

Errore: uncaught exception: [Exception... "Component returned failure code: 0x80040111 (NS_ERROR_NOT_AVAILABLE) [nsIXMLHttpRequest.status]" nsresult: "0x80040111 (NS_ERROR_NOT_AVAILABLE)" location: "JS frame :: http://127.0.0.1/Keratox2.1/Scripts/add_download.js :: takeResponse :: line 11" data: no]

[keratox]

up...

[keratox]

up!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!

[keratox]

up ?