滚动到特定位置菜单固定的效果

.chan-top{top: 416px;}
.abs-top{
    position: absolute;
    margin-left: -691px;
}
.fixed-top{
    position: fixed;
    margin-left: -600px;
    top: 0;
}

<div class="ans-box chan-top abs-top" style="height: 312px; left: 50%;"></div>

$(window).scroll(function(){
    var s=$(window).scrollTop();
    console.log(s);
    if(s >= 416){
        $('.ans-box').removeClass('chan-top');
        $('.ans-box').removeClass('abs-top');
        $('.ans-box').addClass('fixed-top');

    }else {
        $('.ans-box').addClass('chan-top');
        $('.ans-box').removeClass('fixed-top');
        $('.ans-box').addClass('abs-top');
    }
});