Javascript-CheckBoxList 控制

//CheckBoxList至少选择一项

function isselect() {
            var dutyflag = 0;
            var checkobj = document.getElementByIdx_x("CheckBoxList1");
            var checks = checkobj.getElementsByTagName_r("input");
            for (var n = 0; n < checks.length; n++) {
                if (checks[n].type == "checkbox" && checks[n].checked == true) {
                    dutyflag = 1;
                }
            }
            if (dutyflag == 0) {
                alert("请至少选择1项");
                return false;
            }
            return true;
        }

 //CheckBoxList选择不得超过三项  

function check(cblistID) {
            var i = 0;
            var cbID = cblistID + "$" + i;
            var count = 0;
            while (document.getElementsByName(cbID).length > 0) {
                if (document.getElementsByName(cbID)[0].checked) { count++; }
 
                i++;
                var cbID = cblistID + "$" + i;
            }
            if (count > 3) {
                alert("最多只能选中3项");
                event.returnValue = null;
            }
        }

 //后台代码

 

CheckBoxList1.Attributes.Add("onclick", "check('" + CheckBoxList1.ClientID + "');");