I followed your below link

JavaScript not working in UpdatePanel after PostBack in ASP.Net

I am using below Javascript plugin for enabling searchable option in dropdonw list,issue is that when i insert record from gridview,then dropdown searchable option get disable.

<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/select2/4.0.3/css/select2.min.css" />
<script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/select2/4.0.3/js/select2.min.js"></script>
<script type="text/javascript">
    $(function () {
        $(".js-example-placeholder-single").select2({
            placeholder: "Select",
            allowClear: true
        });
</script>

<div style ="height:800px; width:1080px; overflow:auto;" class="center">
     <asp:ScriptManager ID="ScriptManager1" runat="server"></asp:ScriptManager>
 
     <asp:TextBox ID="searchono" Visible="false" runat="server"></asp:TextBox>
     <asp:Label ID="lbmsg" runat="server" Text=""></asp:Label>
  
     <asp:UpdatePanel runat="server" ID="UP_MainList" UpdateMode="Conditional">
         <ContentTemplate>
         <asp:GridView ID="gv1" runat="server" AutoGenerateColumns ="False"   class="table table-striped table-bordered table-hover CenteredGrid" Font-Size="small"

            onrowdatabound="gv1_RowDataBound" onrowdeleting="gv1_RowDeleting"

            onrowediting="gv1_RowEditing" DataKeyNames="IDOD" ShowFooter="True"

            onrowcommand="gv1_RowCommand" onrowupdating="gv1_RowUpdating"

            BackColor="White" BorderColor="White" BorderStyle="Ridge" BorderWidth="2px"

            CellPadding="3" GridLines="None" CellSpacing="1"

            onrowcancelingedit="gv1_RowCancelingEdit" >
        <Columns >
        <asp:TemplateField HeaderText="IDOD">
        <ItemTemplate>
        <asp:Label ID="lblIDOD" runat="server" Text='<%#Eval("IDOD") %>'></asp:Label>
        </ItemTemplate>
        <EditItemTemplate >
            <asp:Label ID="lblIDOD" runat="server" Text='<%#Eval("IDOD") %>'></asp:Label>
            </EditItemTemplate>
            <FooterTemplate >
                <asp:LinkButton ID="lnkinsert" runat="server" Text= "Insert" CommandName="Insert" ></asp:LinkButton>
            </FooterTemplate>
            </asp:TemplateField>
              <asp:TemplateField HeaderText="Ref_ID">
        <ItemTemplate>
        <%--<%# Eval("Order_Ref_No") %>--%> 
                <asp:Label ID="Order_Ref_No" Width="80px" runat="server" Text='<%#Eval("Order_Ref_No") %>'></asp:Label>
        </ItemTemplate>
            </asp:TemplateField>
               <asp:TemplateField HeaderText="OrderNo">
        <ItemTemplate>   
               <asp:Label ID="OrderNo" Width="80px" runat="server" Text='<%#Eval("OrderNo") %>'></asp:Label>
        </ItemTemplate>
            <FooterTemplate >                                <%--<asp:TextBox ID="txtaddOrderNo" runat="server"></asp:TextBox>--%>

            </FooterTemplate>
            </asp:TemplateField>
<%--               <asp:TemplateField HeaderText="Codeitem" Visible="false">
        <ItemTemplate>   
               <asp:Label ID="Codeitem" Width="80px" runat="server" Text='<%#Eval("Codeitem") %>'></asp:Label>
        </ItemTemplate>
        
            </asp:TemplateField>--%>

            <asp:TemplateField HeaderText="ItemName">
            <ItemTemplate>
            <%#Eval("Descriptionitem") %>
                    
            </ItemTemplate>
     
            <FooterTemplate ><label>Item</label>
                <asp:DropDownList ID="ddladdDescriptionitem" runat="server" CssClass="form-control js-example-placeholder-single" Width="150px">
                </asp:DropDownList>
            </FooterTemplate>
            </asp:TemplateField>
                      <asp:TemplateField HeaderText="Alias">
            <ItemTemplate>
            <%#Eval("D_Item") %>
            </ItemTemplate>
            <EditItemTemplate >
                <asp:TextBox ID="D_Item" runat="server" Width="150px" Text='<%#Eval("D_Item") %>'></asp:TextBox>
            </EditItemTemplate>
            <FooterTemplate ><label>Alias</label>
                <asp:TextBox ID="txtD_Item"  Width="150px" runat="server"></asp:TextBox>
            </FooterTemplate>
            </asp:TemplateField>
             <asp:TemplateField HeaderText="Quantity">
            <ItemTemplate>
            <%#Eval("orderqty") %>
            </ItemTemplate>
            <EditItemTemplate >
                <asp:TextBox ID="txtqty" runat="server" Width="50px" Text='<%#Eval("orderqty") %>'></asp:TextBox>
            </EditItemTemplate>
            <FooterTemplate ><label>Qty</label>
                <asp:TextBox ID="txtaddqty"  Width="50px" runat="server"></asp:TextBox>
            </FooterTemplate>
            </asp:TemplateField>

            <asp:TemplateField HeaderText="Produce">
            <ItemTemplate>
    
                   <asp:Label ID="Produce" runat="server" Text='<%#Eval("Produce") %>'></asp:Label>
            </ItemTemplate>      
            </asp:TemplateField>
                <asp:TemplateField HeaderText="Pending">
            <ItemTemplate>
            <%#Eval("Pending") %>
            </ItemTemplate>      
            </asp:TemplateField>


             <asp:TemplateField HeaderText="Rate">
            <ItemTemplate>
            <%#Eval("Item_Rate") %>
            </ItemTemplate>
            <EditItemTemplate >
                <asp:TextBox ID="txtItem_Rate" runat="server" Width="50px" Text='<%#Eval("Item_Rate") %>'></asp:TextBox>
            </EditItemTemplate>
            <FooterTemplate ><label>Rate</label>
                <asp:TextBox ID="txtItem_Rate"  Width="50px" runat="server"></asp:TextBox>
            </FooterTemplate>
            </asp:TemplateField>  
                       <asp:CommandField HeaderText="Edit" ControlStyle-CssClass="fa fa-pencil" ControlStyle-ForeColor="Blue" ShowEditButton="true" EditText="" ControlStyle-Width="60px" > </asp:CommandField>
            <asp:TemplateField>
            <ItemTemplate>
            <asp:LinkButton CommandName ="Delete" CommandArgument ='<%#Eval("IDOD") %>' runat="server" ID ="lnkdelete" Text="Delete" ></asp:LinkButton>
            </ItemTemplate>
            </asp:TemplateField>
        </Columns>
    </asp:GridView>
    <asp:TextBox ID="txtempid" Visible="false" runat="server"></asp:TextBox>
    </ContentTemplate>
</asp:UpdatePanel>
</div>