var hobby = document.getElementsByTagName("input");
            for(i = 0;i < hobby.length;i++){
                    if(hobby[i].type == "checkbox"){
                      hobby[i].checked = true;   }
                  }
        }
        function clearall(){
            var hobby = document.getElementsByName("hobby");
            for(i = 0;i < hobby.length;i++){
                hobby[i].checked = false;}
        }