Gridview Header Checkbox Select and Deselect using client side JavaScript.

I am assuming that we have a Gridview control with Checkboxes inside it.

Now,write a javascript code as

<script type="text/javascript" language="javascript">
function Check_UncheckAll(Checkbox) 
{
    var Grid_vw_Emp = document.getElementById("<%=grid_emp.ClientID %>");

    for (i = 1;i<= Grid_vw_Emp.rows.length-1;i++) 
    {
        Grid_vw_Emp.rows[i].cells[0].getElementsByTagName("INPUT")[0].checked = Checkbox.checked;
    }
}
</script>

Here,cells[0] means 0 index that is Checkbox index position.
Call above Javascript method on Checkbox OnClick event as:-

<HeaderTemplate>
    <asp:CheckBox ID="chkboxSelectAll" runat="server" onclick = "Check_UncheckAll(this);" />
</HeaderTemplate>