how to bind dropdown values from another dropdown onchange event using javascript in asp.net

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ASP.NET

Javascript

Dear all,
i need to bind dropdown values based on value selected from another dropdown in asp.net, but with out doing postback.for that i have used javascript. i used enablepage methods function to retrive data from server side to javascript and all values are coming..but i am unable to bind those values to required dropdown.please help me how to solve this.
my code is as follows.

<asp:ScriptManager ID="scm1" runat="server" EnablePageMethods="true">
1st dropdown
====================

<asp:DropDownList ID="ddlBranch" runat="server" onchange="BindEmployeeNames()" data-md-selectize>
                                        <asp:ListItem Value="0">Select</asp:ListItem>
                                    </asp:DropDownList>

Note:-for this ddl data is coming dynamically on page load.

2nd dropdown
========================

<asp:DropDownList ID="ddlEmployeeNames" runat="server" data-md-selectize>
                                    </asp:DropDownList>

my javascript:-
=======================

var ddlEmployeeNamesItems;
        function BindEmployeeNames() {
            //alert("k");
            var ddlBranchCtrl = document.getElementById("<%=ddlBranch.ClientID %>");
                ddlEmployeeNamesItems = document.getElementById("<%=ddlEmployeeNames.ClientID %>");
                ddlEmployeeNamesItems.options.length == 0;
                // alert(ddlBranchCtrl.options[ddlBranchCtrl.selectedIndex].value);
                PageMethods.FillEmpData(ddlBranchCtrl.options[ddlBranchCtrl.selectedIndex].value, OnSuccess);
            }
            function OnSuccess(response) {
                //alert(response);
                ddlEmployeeNamesItems.options.length = 0;
                AddOption("Select", "0");
                for (var i in response) {
                    //alert(response[i].Name + "------------" + response[i].Id);
                    AddOption(response[i].Name, response[i].Id);
                }
            }
            function AddOption(text, value) {
                var option = document.createElement('option');
                option.value = value;
                option.innerHTML = text;
                document.getElementById("<%=ddlEmployeeNames.ClientID %>").options.add(option);

            }

please help me to solve this...
Thanks.