title: JavaScript: How to block the whole screen while waiting for ajax response
body: <p>I have a screen in which there are different functions. There is a dropdown box onchange of which an Ajax call goes and a jsp page is returned in response. This response i then put inside a div below my dropdown box. 
          Now what i want is that untill this jsp is not filled in the div element the screen is blocked either by an alert box or some other dialog box.
      How can i achieve this ?</p>