How to disable postback on an asp Button (System.Web.UI.WebControls.Button)
Solution 1:
Have your javascript return false when it's done.
<asp:button runat="server".... OnClientClick="myfunction(); return false;" />
Solution 2:
YourButton.Attributes.Add("onclick", "return false");
or
<asp:button runat="server" ... OnClientClick="return false" />