[Torch`Ok]

<script>
      !function () {
         
      var elem =  document.getElementById('win');
      var child = elem.getElementsByClassName('inviz');// TypeError: elem is null 
       var button = document.getElementById('getdiv');
       var leng = child.length;
       var i = 0;
         
        
        button.onclick = function (e) {
          
           
        if (i >= leng) return; 
           
       child[0].className = 'happyend';
          
        i++;
        return false;
           
        }
           
       }();
  
    </script>