jq 解决当scroll滚动定位元素抖动问题

 var timer = null;
    $(window).scroll(function () {
        clearTimeout(timer);
        timer = setTimeout(function () {
            //代码...
            //$login.css('top',($(window).height() -                         
              $login.outerHeight())/2+$(document).scrollTop());
        }, 10)
    });