Use the ImageButton.OnClientClick property to specify additional client-side script that executes when an System.Web.UI.WebControls.ImageButton control's ImageButton.Click event is raised. The script that you specify for this property is rendered in the System.Web.UI.WebControls.ImageButton control's OnClick attribute in addition to the control's predefined client-side script.

This property cannot be set by themes or style sheet themes. For more information, see System.Web.UI.ThemeableAttribute and ASP.NET Themes Overview.