How to fire server side event for Textbox Lostfocus throuth client side javascript

[mackpag]

i want to save the data which is written in textbox when i exit from the textbox that means when i lost the focus from textbox. the textbox is in the grid. so how to do that. the grid is in UpdatePanel of AJAX. sending the source

<div>
        <asp:ScriptManager ID="ScriptManager1" runat="server">
        </asp:ScriptManager>
        <br />
        <asp:UpdatePanel ID="UpdatePanel1" runat="server">
            <ContentTemplate>
                <asp:GridView ID="grdInventory" runat="server"  DataKeyNames="ID,SalesmanID" AutoGenerateColumns="False">
                    <Columns>
                        <asp:BoundField DataField="StockID" HeaderText="StockID" SortExpression="StockID" />
                        <asp:BoundField DataField="PartName" HeaderText="Part Name" SortExpression="PartName" />
                        <asp:TemplateField HeaderText="Quantity">
                            <ItemTemplate>
                                <asp:TextBox ID="txtQuantity" runat="server" Text='<%# DataBinder.Eval( Container, "DataItem.Quantity") %>' AutoPostBack="True"></asp:TextBox>
                            </ItemTemplate>
                        </asp:TemplateField>
                    </Columns>
                </asp:GridView>
            </ContentTemplate>
        </asp:UpdatePanel>
 
    </div>