jquery实现返回顶部动画

<a href="javascript:;" class="gotop" id="scroll" sty>返回顶部</a>
<script type="text/javascript">
                $(function(){
                    showScroll();
                    function showScroll(){
                        $(window).scroll( function() { 
                            var scrollValue=$(window).scrollTop();
                            scrollValue > 100 ? $('.gotop').fadeIn():$('.gotop').fadeOut();
                        } );    
                        $('#scroll').click(function(){
                            $("html,body").animate({scrollTop:0},500);  
                        }); 
                    }
                })
            </script>