如何实现返回顶部功能

jsp代码

<span id="assetToTop" class="commentTop" style="cursor:pointer; width: 54px;height: 54px;background-image: url('browse/images/zxb/top.png');position: fixed;left: 72%;top: 85%;margin-left: 26px;">返回顶部</span>

js代码

$().ready(function(){ //dom加载完后调用$('#baseModal').on('scroll',function(){var winHeight = $(window).height();var scrollTop = $('#baseModal').scrollTop();if( scrollTop > winHeight * 0.3 ){$('#assetToTop').css('display','');}else{$('#assetToTop').css('display','none');}});});$('#assetToTop').on('click',function(e){$('#baseModal').scrollTop(0);});