Nginx support for AJAX requests

http://stackoverflow.com/questions/9025398/spree-administration-ajax-request-works-in-development-404s-in-production

location ~* \.(js|css|jpg|jpeg|gif)$ {
    passenger_enabled on;
    if (-f $request_filename) {
        expires                        max;
        break;
    }
}

http://stackoverflow.com/questions/1737314/nginx-raises-404-when-using-format-js

location ~* \.(ico|css|js|gif|jp?g|png)(\?[0-9]+)?$ {
       expires max;
       break;
     }

location ~* \.(ico|css|js$|gif|jp?g|png)(\?[0-9]+)?$ {
    expires max;
    break;
}

or

location ~* ^.+\.(jpg|jpeg|gif|png|css|swf|ico|mov|flv|fla|pdf|zip|rar|doc|xls)$
{
    expires 12h;
    add_header  Cache-Control  private;
}
location ~* ^/javascripts.+\.js$
{
    expires 12h;
    add_header  Cache-Control  private;
}