//设置窗口滚动条高度

function setScrollTop(top){

      if(!isNaN(top))document.body.scrollTop = top;

}

//取窗口滚动条高度

    function getScrollTop(){

        var scrollTop=0;

        if(document.documentElement&&document.documentElement.scrollTop){

            scrollTop=document.documentElement.scrollTop;

        }else if(document.body){

            scrollTop=document.body.scrollTop;

        }

        return scrollTop;

    }