How to disable postback on an asp Button (System.Web.UI.WebControls.Button)
Have your javascript return false when it's done.
<asp:button runat="server".... OnClientClick="myfunction(); return false;" />
YourButton.Attributes.Add("onclick", "return false");
or
<asp:button runat="server" ... OnClientClick="return false" />
You can use jquery click action and use the preventDefault() function to avoid postback
<asp:button ID="btnMyButton" runat="server" Text="MyButton" />
$("#btnMyButton").click(function (e) {
// some actions here
e.preventDefault();
}