how to call javascript function after databind to gridview

If you are using ItemTemplate in your gridView then you need to enable "RowDataBound" inside properties pane ->Events.
Steps to execute Javascript function.
1.Javascript function in your aspx page

function fnPopUp(viewDetails) {
        alert(viewDetails);
    }

2. Create templateField :

<asp:TemplateField HeaderText="View Information">
        <ItemTemplate>
        <asp:LinkButton ID="lnkDisplayPopUp" runat="server"
                Text='<%# Eval("ColumnName") %>' onclick="lnkDisplayPopUp_Click" ></asp:LinkButton>

            &nbsp;

        </ItemTemplate>
        </asp:TemplateField>

3. In events inside properties Pane of GridView RowDataBound specify (GridView_RowDataBound) name of the function which is created behind GridView code file .
3. Write This Code.In order to register your onclick event.

protected void GridView_RowDataBound(object sender, GridViewRowEventArgs e)
        {
            if (e.Row.RowType == DataControlRowType.DataRow)
            {
                LinkButton btnAlert = (LinkButton)e.Row.FindControl("lnkDisplayPopUp");
                DataRowView drv = (DataRowView)e.Row.DataItem;
                string id = drv["ColumnName"].ToString();
                btnAlert.Attributes.Add("onclick", "fnPopUp("+id+");return false;");
            }
        }

protected void gvListDTL_RowDataBound(object sender, GridViewRowEventArgs e)
       {
           if (e.Row.RowType == DataControlRowType.DataRow)
           {
               try
               {
                   HiddenField hdnRM_Qty = (HiddenField)e.Row.FindControl("hdnRM_Qty");
                   TextBox RM_Qty = (TextBox)e.Row.FindControl("RM_Qty");
                   RM_Qty.Attributes.Add("onchange", "FnValidate('"+hdnRM_Qty.ClientID+"','"+RM_Qty.ClientID+"')");
               }
               catch (Exception)
               { }
           }
       }