<script>
  
  _EditorOnLoad();
  
  function _EditorOnLoad()
  {
       // get the cute editor instance
       var editor1 = document.getElementById('<%=Editor1.ClientID%>');
   
       //Get the editor content  
       var editdoc=editor1.GetDocument();   
       if(!editdoc.body) //Not Ready
       {
            setTimeout(_EditorOnLoad,10);
            return;
       }
       else
       {   
            // Set the editor 
            editor1.setHTML("Hello");
       }
  }

  </script>