JavaScript

//this will return all the inputs inside the table1
var ele = document.getElementById('table1').getElementByTagName('input')
//you can filter out it using type
for(var c=0;c < ele.length; c++){
   if(ele[c].type=='checkbox'){
       //do the code....
   }
}

//get all the checkbox of table 1
var ele = document.getElementById("table1").getElementsByTagName("input");
var size = ele.length;
var boxs = [];
var j=0;
for(var i=0;i<size;i++){
    //check the element attributes
    if(ele[i].type=="checkbox" and ele[i].name=="CHK1"){
        boxs[j++]=ele[i];
    }
}
//here boxs is the object what you want.

//place in the window keydown event

//IE
e.cancelBubble=true;
e.returnValue = false;

//FF
if (e.stopPropagation){
  e.stopPropagation();
  e.preventDefault();

Protected Sub gvT_RowCreated(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewRowEventArgs) Handles gvT.RowCreated

    If e.Row.RowType = DataControlRowType.Footer Then
        e.Row.ID = "theFooter"
    End If

End Sub

function toggleFooter()
{
    var ftr = document.getElementById('<%=gvT.ClientID %>_theFooter');
    if (ftr.style.display != 'none')
        ftr.style.display = 'none';
    else
        ftr.style.display = '';
}

<asp:gridview id="gvT" runat="server" showfooter="true" autogeneratecolumns="false">
	<columns>
		<asp:templatefield>
			<itemtemplate>
				<%#Eval("MyField") %>
			</itemtemplate>
			<footertemplate>
				<asp:label id="lblFooterLabel1" runat="server"></asp:label>
			</footertemplate>
		</asp:templatefield>
	</columns>
</asp:gridview>

function getFooterLabel()
{
    var lbl = document.getElementById('&<%=gvT.ClientID %>_theFooter_lblFooterLabel1');
            return lbl;
}

for(var i = 0;i < document.childNodes.length;i++){
		if(document.childNodes[i].tagName != undefined)
                .....
}