Getting the response header

http://stackoverflow.com/a/2444499/517457

$(document).ready(function() { 
    $("[name='submit']").click(function() { 
        $.ajax({
            type: "POST",
            data: $(".form-signup").serialize(),
            url: "external.asp", 
            success: function(output, status, xhr) { 
              alert(xhr.getResponseHeader("Content-Length"));
            },
            error: function(output) {
              $('.sysMsg').html(output);
            }
        }); 
    }); 
});