貼吧那個返回頂層的代碼實現

$(window).scroll(function(){
                if($(window).scrollTop() > 100){
                    $("#gotop").fadeIn(1000);//一秒漸入動畫
                }else{
                    $("#gotop").fadeOut(1000);//一秒漸隱動畫
                }
            });

<!--css-->
.return-top{
      height: 65px;
      background-position: 0 -30px;
    }
    .side-right a.side-right-dr {
      height: 65px;
      text-align: center;
      background-position: 0 -200px;
    }
	.side-right a.side-right-fav-none {
		height: 65px;
		background-position: 0 -60px;
	}
	.side-right a {
		display: block;
		width: 55px;
		height: 55px;
		margin: 0 0 8px 0;
		background: url(https://img.wisetravel.cn/website/images/kefu/return_top_new.png?v2.00) no-repeat;
	}



<!--右邊豎立的東西html-->
<div class="side-right" id="J_side_right" style="right: 260.5px; bottom: 90px;position:fixed;">
	<a href="javascript:window.scroll(0, 0);" id="J_return_top" class="return-top"></a>
	<a class="side-right-fav-none J_pop_login J_side_fav"></a>
	<a id="J_pre_sale_qq" class="side-right-dr pre_sale_qq zhiCustomBtn"></a>
	<a class="side-right-fav-none J_pop_login J_side_fav"></a>
</div>