How to get the gridview item template element in javascript

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false"  >
            <Columns>
                <asp:TemplateField>
                <ItemTemplate>
                 <asp:TextBox ID="Textbox1" runat="server" CssClass="DropDownFont" Font-Size="XX-Small" Text='<%# Eval("Column1")%>' > </asp:TextBox>
                </ItemTemplate>
                </asp:TemplateField>
            </Columns>
        </asp:GridView>
        <script type="text/javascript">
            var table = document.getElementById("GridView1");

            if (table.rows.length > 0) {
                //loop the gridview table
                for (var i = 1; i < table.rows.length; i++)
                {
                    //get all the input elements
                    var inputs = table.rows[i].getElementsByTagName("input");
                    for (var j = 0; j < inputs.length; j++) {
                        //get the textbox1
                        if (inputs[j].id.indexOf("Textbox1") > -1) {
                            alert(inputs[j].value);
                        }

                    }

                }
            }

        </script>