<script type="text/javascript" language="javascript" >   

       function ff() {  

       var checkd = document.getElementById("Checkbox4");       

                if (checkd.checked == true)   //判段是否选中   在要选中的标签中插入属性 οnclick=“ff();”

       {      

            var val = document.getElementsByTagName("input");         //获取所有的input元素

          for (var i = 0; i < val.length; i++) {         

             val[i].checked = true;     

                                                           }           

                              }    

          else {          

        var val = document.getElementsByTagName("input");          //获取所有的input元素  

       for (var i = 0; i < val.length; i++) {               

       val[i].checked = false;         

         }

             }       

   }    

  </script>