GridView Header Text in asp.net using asp:BoundField

I want to change the header text of the gridview using Design..

<asp:BoundField HeaderText="">

i created a variable in javascript and initialize variable defending on the condition and then i tried to call that variable over here as below:

<asp:BoundField HeaderText="Text Here" DataField="slno" >

here I use "text here" string stored in one variavble name . and i want to use that variable

My code :

 <script type="text/javascript" language="javascript">
 /// <summary>
 /// TO ACCESS COOKIE VARIABLE
 /// </summary>
 var flag;
 var ca = document.cookie.split('=');
 for (var i = 0; i < ca.length; i++) {
    var c = ca[i];
    while (c.charAt(0) == ',') c = c.substring(1);
}
if (c != '' && c != null) {
    flag = c;
}
else {
    flag = 1;
}
//*********************************************
if (flag == 1) {
    var name_lbl = "Hai";
}
else if (flag == 2) {
    var name_lbl = "How are you?";
}
</script>
//------------------------------------------------
</asp:Content>
<form id="form1" runat="server">
</table>

<div style="overflow: auto; height: 99%;" id="divTable">
<table><tr><td>
<label for='field ID'>&nbsp;<b><input type="text" id="kilist_lbl" size="20"         style="border: none; height:20px" readonly/></b>&nbsp;&nbsp;</label> <br />
</td></tr></table>

<asp:GridView ID="gvareadetails" runat="server"  
CssClass="mGrid"  AutoGenerateColumns="False">
<Columns>        
  <%-- here is the problem when assigning ID to headerText label --%>
     <asp:BoundField HeaderText='sss' DataField="slno" >  
    <ItemStyle Width="5%" />
    </asp:BoundField>
 </Columns>
 </asp:GridView>
 </div>
 </form>

 <script type="text/javascript" language="javascript">
 document.getElementById('sss').value = name_lbl;
 </script>

 </asp:Content>

Any one have any suggestions how this could be achieved..

Instead of js, just try the C# code to get values from the grid view.

ex:

int name_lbl = gvareadetails.Columns[0][0];

Here Columns[0][0] gives you the first row first column value.