How to getElementByid() dynamic datagrid inside DataList()

<script language="javascript">

function ()

{ 

var tblGrid = document.getElementById("dgDashboard");

 }

</script>

'>'>'>' ReadOnly="True"><asp:datalist
id="dlDashboard" Runat="server"
CssClass="dataItemsStyle1"
OnItemCommand="dlDashboard_ItemCommand"
                  OnItemDataBound="dlDashboard_ItemDataBound"
CellPadding="1" CellSpacing="7"
DataKeyField="inte_Defect_HeadingId">
                  <ItemStyle Width="600px"></ItemStyle>
                  <ItemTemplate>
                   <asp:imagebutton id="btnImg1"
Runat="server" ImageUrl="images/plus.gif"
AlternateText="Click to show matrix"
                    CommandName="Expand"></asp:imagebutton>
                   <asp:Label ID="lblDefectField" Runat=server
CssClass=lblStyle Text=''>
                   </asp:Label>&nbsp;[
                   <asp:Label ID="lblOpporCnt" Runat=server
CssClass=lblSubHeadStyle '>
                   </asp:Label>]
                  </ItemTemplate>
                  <SelectedItemTemplate>
                   <asp:ImageButton ID="btnImg1"
CommandName="Collapse" ImageUrl="images/minus.gif"
runat="server" AlternateText="Click to hide matrix"
                    ImageAlign="AbsMiddle" />
                   <asp:Label ID="lblDefectField" Runat=server
CssClass=lblStyle Font-Bold="True"'>
                   </asp:Label>
                   <asp:Label ID="lblAltCnt" Runat=server
CssClass=labelHeading Text='' Visible=False>
                   </asp:Label>&nbsp;
                   <asp:Label ID="lblChangeQry"
Runat="server" CssClass="lblStyle"
Font-Bold="True">&nbsp;&nbsp;&nbsp;&nbsp;Quantity
:</asp:Label>
                   &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
                   <asp:textbox onkeypress="return
checkNumber(event)" id="txtChangeQty" runat="server"
CssClass="txtSmall"
                    Width="30px" Text="0"
MaxLength="4"></asp:textbox>
                   <asp:ImageButton id="btnGo"
Runat="server" OnClick="ChangeQty"
ImageUrl="Images/apply_fpy.jpg"></asp:ImageButton>

' ReadOnly="True">
                   <asp:DataGrid id="dgDashboard"
Runat="server" ShowFooter="true" ShowHeader="true"
AutoGenerateColumns="false"
                    OnItemDataBound="dgDashboard_ItemDataBound">
                    <HeaderStyle VerticalAlign="Middle"
Font-Size="XX-Small" Font-Names="Verdana"
Font-Bold="True"
                     ForeColor="Black" BackColor="#C9C9C9"
CssClass="dataHeadStyleNew"
Height="20"></HeaderStyle>
                    <ItemStyle Font-Size="XX-Small"
Font-Names="Verdana" ForeColor="Black"
BackColor="#DFDFDF"></ItemStyle>
                    <AlternatingItemStyle Font-Size="XX-Small"
Font-Names="Verdana" ForeColor="Black"
BackColor="#E7DCD5"></AlternatingItemStyle>
                    <Columns>
                     <asp:TemplateColumn HeaderText="DefectFieldId"
Visible="false">
                      <ItemTemplate>
                       <asp:Label ID=lblDefectFieldID Runat=server
Text='") %>'>
                       </asp:Label>
                       </asp:TextBox>
                      </ItemTemplate>
                     </asp:TemplateColumn>
                     <asp:TemplateColumn
HeaderText="DefectFieldId">
                      <ItemTemplate>
                       <asp:Label ID="Label1" Runat=server
Text=''>
                       </asp:Label>
                       </asp:TextBox>
                      </ItemTemplate>
                     </asp:TemplateColumn>
                     <asp:TemplateColumn
HeaderText="inte_DE_Serial_" Visible="False">
                      <ItemTemplate>
                       <asp:Label ID="lblDESerial" Runat=server
Text=''>
                       </asp:Label>
                       </asp:TextBox>
                      </ItemTemplate>
                     </asp:TemplateColumn>
                     <asp:TemplateColumn HeaderText="No. of
Opportunities">
                      <ItemTemplate>
                       <asp:TextBox ID="txtNumOpportunities"
onkeyup="keyPressed('dgDashboard')" CssClass=txtSmall Runat=server
Width=30 ReadOnly=True                        </asp:TextBox>
                      </ItemTemplate>
                     </asp:TemplateColumn>

' ReadOnly="True"></Columns>
                   </asp:DataGrid>
                  </SelectedItemTemplate>
                 </asp:datalist>

Thanks