使用jQuery实现返回顶部

<a id="go2" class="go2" href="#header"><span class="go2-inner"></span></a>
<script type="text/javascript">
$(function(){
    $('#go2').click(function(){
        $("html,body").animate({scrollTop:0},200);
        return false;
    });
    $(window).scroll(function(){
        var obj=$('#go2');
        if(obj.offset().>900){
            obj.show();
        }else{
            obj.hide();
        }
    });
});
</script>

.go2 {
    background: url("") no-repeat scroll left transparent;
    bottom: 65px;
    color: #444444;
    display: none;
    height: 50px;
    margin-left: 510px;
    position: fixed;
    right: 160px;
    text-align: center;
    width: 50px;
}
.go2:hover {
    background-position: -50px ;
}