<asp:Button id="DeleteButton" runat="server" Text="Delete" 
            OnClick ="delete_clickhandler" 
            OnClientClick="return confirm('Are you sure you want to?');" />

或者,您可以在javascript中调用方法

<asp:Button id="DeleteButton" runat="server" Text="Delete" 
            OnClick ="delete_clickhandler" 
            OnClientClick="return MyDeleteConfirm();" />

MyDeleteConfirm()做了更精细的事情,但如果你不想删除则返回false.