判斷HTML中的checkbox是否被選中

      //合法性驗證
        function checkValidity() {
            var userNameCheck = $("#userNameCheck").attr('checked');
            var dateCheck = $("#dateCheck").attr('checked');
            var descCheck = $("#descCheck").attr('checked');
            if (!userNameCheck && !dateCheck && !descCheck) {
                alert("至少要勾選一個");
                return false;
            }
            return true;
        }

    var checkUserName = $("#checkUserName").is(":checked");
                var checkOperateTime = $("#checkOperateTime").is(":checked");
                var checkdescriptionInclude = $("#checkdescriptionInclude").is(":checked");
                if (!checkUserName && !checkOperateTime && !checkdescriptionInclude) {
                    alert("至少選擇一種條件查詢");
                    return;
                }