this is what i have implemented, for further code, how to send this text of the text box to the server to store in variable or database without post back. it can be done by using ajax and update plane but i wold like to implement it using javascript script.

<div id="CommentID" style=" width:30%; height:30%">   

   <asp:Button ID="Button1" runat="server"
        Text="Comment" 
        OnClientClick="visibleDiv('id1'); return false;" />




<div id="id1" runat="server" style="visibility: hidden; background-color:Green; width:100%; height:100%">
<asp:TextBox ID="TextBox1" runat="server" AutoCompleteType="Disabled" Rows="3" 
        TextMode="MultiLine" Width="98%"></asp:TextBox>
<asp:Button ID="Button2" runat="server" Text="Post" onclick="Button2_Click" />
    <asp:Button ID="Button3" runat="server" Text="Cancel" OnClientClick="visibleDiv('id1'); return false;" />
</div>






</div>