jQuery and AJAX response header

So I've got this jQuery AJAX call, and the response comes from the server in the form of a 302 redirect. I'd like to take this redirect and load it in an iframe, but when I try to view the header info with a javascript alert, it comes up null, even though firebug sees it correctly.

Here's the code, if it'll help:

$j.ajax({
    type: 'POST',
    url:'url.do',
    data: formData,
    complete: function(resp){
        alert(resp.getAllResponseHeaders());
    }
});

I don't really have access to the server-side stuff in order to move the URL to the response body, which I know would be the easiest solution, so any help with the parsing of the header would be fantastic.

cballou's solution will work if you are using an old version of jquery. In newer versions you can also try:

  $.ajax({
   type: 'POST',
   url:'url.do',
   data: formData,
   success: function(data, textStatus, request){
        alert(request.getResponseHeader('some_header'));
   },
   error: function (request, textStatus, errorThrown) {
        alert(request.getResponseHeader('some_header'));
   }
  });

According to docs the XMLHttpRequest object is available as of jQuery 1.4.

If this is a CORS request, you may see all headers in debug tools (such as Chrome->Inspect Element->Network), but the xHR object will only retrieve the header (via xhr.getResponseHeader('Header')) if such a header is a simple response header:

• Content-Type
• Last-modified
• Content-Language
• Cache-Control
• Expires
• Pragma

If it is not in this set, it must be present in the Access-Control-Expose-Headers header returned by the server.

About the case in question, if it is a CORS request, one will only be able to retrieve the Location header through the XMLHttpRequest object if, and only if, the header below is also present:

Access-Control-Expose-Headers: Location

If its not a CORS request, XMLHttpRequest will have no problem retrieving it.