调用JQUERY返回顶部功能

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>jq3</title>
    <style>
        .back{
  
            position: fixed;
            right: 0px;
            bottom: 0px;
        }
        .heid{
  
            display: none;
        }
     </style>
</head>
<body>
<div style="height: 2000px"></div>
<div id ='ck' οnclick="gotop()" class="back heid">GotoTop</div>
<script type="text/javascript" src="jquery-2.2.4.js"></script>
<script type="text/javascript">
    function gotop(){
  
        $(window).scrollTop(0)
    }
   $(function(){
  
       $(window).scroll(function(){
  
          var top=$(window).scrollTop()
           if (top > 100){
  
               $('#ck').removeClass('heid')
           }else{
  
               $('#ck').addClass('heid')
           }
       });
   });h

</script>
</body>
</html>