<com:TContent ID="Content"> <h1>Callback Enabled Calculator 2</h1> <com:TTextBox id="a" /> + <com:TTextBox id="b" /> = <com:TActivePanel id="panel1"> <com:TTextBox id="c" /> </com:TActivePanel> <com:TButton id="sum" onclick="do_sum" text="Calculate!" /> <com:TRequiredFieldValidator ControlToValidate="a" ErrorMessage="left summand is required." ControlCssClass="required" Display="None" /> <com:TRequiredFieldValidator ControlToValidate="b" ErrorMessage="right summand is requied." ControlCssClass="required" Display="None" /> <div class="summarybox"> <com:TValidationSummary ID="summary" HeaderText="Unable to calculate because" /> </div> <com:TCallback ID="callback1" OnCallback="update_callback" /> <script> $("<%= $this->sum->ClientID %>").onclick = function(event) { <%= $this->callback1->ActiveControl->Javascript %> return false; }; </script> </com:TContent>