function checkall(){
            var hobby = document.getElementsByName("hobby");
         
          // 任务1
           for(var a=0;a<hobby.length;a++){
               hobby[a].checked=true;  //全选
           }
        }
        function clearall(){
            var hobby = document.getElementsByName("hobby");
           
         // 任务2   
            for(var a=0;a<hobby.length;a++){
               hobby[a].checked=false;  //全不选
           }
        }
       
        function checkone(){
            var j=document.getElementById("wb").value;
       
         // 任务3
        //alert(j)
        var s = j.split("");
           for(var a=0;a<s.length;a++){
               var h = "hobby"+s[a]; //拼id值
                var j=document.getElementById(h);
                j.checked=true;
           }
       
        }