I tried out a sample like this
ASPX Code
<asp:GridView ID="gv" runat="server" AutoGenerateColumns="false">
<Columns>
<asp:TemplateField HeaderText="check">
<ItemTemplate>
<asp:Label ID="lbl" runat="server" Text='<%#Eval("iso") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
</Columns>
the Gridview
generated the following HTML -
<table cellspacing="0" rules="all" border="1" id="gv" style="border-collapse:collapse;">
<tr>
<th scope="col">check</th>
</tr>
<tr>
<td>
<span id="gv_ctl02_lbl">ab</span>
</td>
</tr>
<tr>
<td>
<span id="gv_ctl03_lbl">ab</span>
</td>
</tr>
<tr>
<td>
<span id="gv_ctl04_lbl">ab</span>
</td>
</tr>
</table>
as you can see for my case the span id started from 2.
so i tried the following javascript
for(i=2;i<5;i++) console.log(document.getElementById('gv_ctl0'+i+'_lbl').innerHTML);
and the result was
ab
ab
ab
I tried it out in chrome and firefox(firebug). both are working fine.