$(document).ready(function() {

function enable(){
  // from http://valums.com/vertical-scrolling-menu/
  // height of area at the top at bottom, that don't respond to mousemove
  var inactiveMargin = 100;
  // Cache for performance
  var wrapperWidth = wrapper.width();
  var wrapperHeight = wrapper.height();
  // Using outer height to include padding too
  var scrollableHeight = scrollable.outerHeight() + 2*inactiveMargin;
  // Do not cache wrapperOffset, because it can change when user resizes window
  // We could use onresize event, but it's just not worth doing that
  // var wrapperOffset = wrapper.offset();

  //When user move mouse over menu
  wrapper.mousemove(function(e){
    var wrapperOffset = wrapper.offset();
    // Scroll menu
    var top = (e.pageY -  wrapperOffset.top) * (scrollableHeight - wrapperHeight) / wrapperHeight  - inactiveMargin;

    if (top < 0){
      top = 0;
    }

    wrapper.scrollTop(top);
  });
}

});