fixed sidebar with variable height

fixed.js

var fixed = false;
var sidebarTop = jQuery('#secondary').offset().top;
var sidebarHeight =  jQuery('#secondary').height();
var windowHeight = jQuery(window).height();
var leftHeight = jQuery('.left-content-area').height();
if (windowHeight < sidebarHeight){
  startPosition = sidebarTop + sidebarHeight - windowHeight;
  fixPosition = windowHeight - sidebarHeight;
  endPosition = leftHeight + sidebarTop - windowHeight;
}else{
  fixPosition = 0;
  startPosition = sidebarTop + sidebarHeight;
  endPosition = sidebarTop;
}
jQuery(window).scroll(function() {  
  var currentScroll = jQuery(window).scrollTop();   
    if (!fixed){
      if (currentScroll >= startPosition){
        fixed = true;
        jQuery('#secondary').css({position:'fixed',top:fixPosition});
      }
    }else{
      if (currentScroll <= startPosition){
        fixed = false;
        jQuery('#secondary').css({position:'relative',top:0});
      }else if (currentScroll >= endPosition){
          jQuery('#secondary').css({position:'relative',top: leftHeight - sidebarHeight });
      }else if (currentScroll <= endPosition){
            jQuery('#secondary').css({position:'fixed',top:fixPosition});
      }
    }
});