jQuery Forum

The .ajax() request has an option called 'xhr'. I am trying to grab
the filesize of a file (html) being requested with ajax. I think that
the method used with XHR is getResponseHeader. How would I implement
this into the 'xhr' option?
I have tried several ways, but all gave me errors on Firebug, such as
that getResponseHeader was not defined.
$.ajax({
...
...
xhr: function(){
alert(    this.getResponseHeader('Content-Length'));
},
...
ect
I have tried this.getResponseHeader('Content-Length'),
xhr.getResponseHeader('Content-Length'), and getResponseHeader
('Content-Length') by itself, but no luck so far.
If I am way off and incorrect, what would be the best way to see if
somehow the file I'm loading has changed (file size, last modified,
ect) from the last request?