checkBox的全选和 反选

 function setChk (a){
    var res="";
    var obj = "";
    var obj = document.getElementsByName("itemlist");
    if(obj.length > 0 ){
  var len = obj.length;
  for (var i = 0 ; i < len ; i ++) {
         if(a==1)
         {
           obj[i].checked = true;
         }else if(a==2)
         {
           obj[i].checked = false;
         }
    
  
    if(obj[i].checked){
     if(res != ""){ res += ",";}
     res += obj[i].value;
    }
   }
    } 
    document.all.checkboxs.value= res;
      
}

---------------------------------------------------form------------------------------------------------------------<input type="checkbox" name="itemlist" value="${list.no}" onclick="setChk(3)" style="border:0px" />

 

 

       <a href="#" onclick="setChk(1)">全选</a>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#" onclick="setChk(2)">反选</a>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<html:submit  value="封号" />