Scroll Bar

Scroll Bar

I'm wondering about how to calculate the height of the scroll bar that I'm creating, following examples:

  1.     <script>
  2.     $( document ).ready(function() {
  3.     $( "#rolagem2" ).height($(document).height() - $(window).height());
  4.     
  5.     $( window ).on('scroll touchmove mousewheel', function(e){
  6.     $( "#rolagem2" ).css('margin-top', $(window).scrollTop());
  7.     });
  8.     
  9.     });
  10.     </script>
#rolagem2 stay with the same size as the standard scroll bar!