Post back event in with out refresh (Using Web method in aspx page)

 Server Side Code

 [WebMethod]
        [ScriptMethod(ResponseFormat = ResponseFormat.Json)]
        public static string GetBindBudgetlineresult(string ID)
        {
            TCA_OSOEntities context = new TCA_OSOEntities();
            

            var PID = Convert.ToInt32(ID);

            var Budgetlineresult = (from MstrBudgetLine tbl in context.MstrBudgetLines
                                    where tbl.IsDeleted == 0 && tbl.IsActive == 1 && tbl.ParenetID == PID
                                    select new
                                    {
                                        BudgetLinesPkID=tbl.BudgetLinesPkID,
                                        BudgetLinesName=tbl.BudgetLinesName

                                    }).ToList();                                     
                                       
               
           
            var jsonSerialiser = new JavaScriptSerializer();
            var jsonresult = jsonSerialiser.Serialize(Budgetlineresult);

            return jsonresult;
        }

Client Side Code

    function ddlparentexpensetype_SelectedIndexChanged(sender, args) {
                // To get the item 
                var item = args.get_item();
                //To get the item text
                var itemText = args.get_item()._text;

                BindBudgetline();

            }

***********************************************


        function BindBudgetline() {
            
            $.ajax({
                type: "POST",
                url: "AddInitiative.aspx/GetBindBudgetlineresult",
                data: '{ID: "' + document.getElementById("<%= ddlparentexpensetype.ClientID %>").control._value + '" }',
                contentType: "application/json; charset=utf-8",
                dataType: "json",
                success: OnBudgetlineSuccess,
                failure: function (response) {
                    alert(response.d);
                }
            });
        }
        function OnBudgetlineSuccess(response) {
          
            var data = JSON.parse(response.d);
            if (data.length != 0) {

                var drop = $find('<%=dropdownbudgetline.ClientID %>');
                drop.clearItems();
                drop.set_text("");

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

                    var combo = $find("<%= dropdownbudgetline.ClientID %>");
                    var comboItem = new Telerik.Web.UI.RadComboBoxItem();
                    comboItem.set_text(data[i]["BudgetLinesName"]);
                    combo.set_value(data[i]["BudgetLinesPkID"]);
                    combo.trackChanges();
                    combo.get_items().add(comboItem);
                    comboItem.select();
                    combo.commitChanges();
                }
            }
            else {

                var drop = $find('<%=dropdownbudgetline.ClientID %>');
                drop.clearItems();
                drop.set_text("");
            }
        }

        /* End*/

        function AmountConvertions() {

            $.ajax({
                type: "POST",
                url: "AddInitiative.aspx/GetConvertedAmount",
                data: "{ 'Amt': '" + document.getElementById("<%= txtrequestedbudgetbyoso.ClientID %>").value + "', 'Osoid': '" + document.getElementById("<%= dropdownoso.ClientID %>").control._value + "'}",
                contentType: "application/json; charset=utf-8",
                dataType: "json",
                success: OnAmountConvertionsSuccess,
                failure: function (response) {
                    alert(response.d);
                }
            });
        }