code: function(){
              var pageYOffset = 0;
              if(window.pageYOffset){
                  pageYOffset = window.pageYOffset;
              }else if(document.documentElement && document.documentElement.scrollTop){
                  pageYOffset = document.documentElement.scrollTop;
              }
              return pageYOffset;
          }
docs: Retrieve the amount of content that has been hidden by scrolling down.
  
  @type Number
  @return 0-n value.