RadComboBox Enter Key

I'm trying to get the enter key to submit a combobox. I tried the following but it doesn't run the btnSave onclick event. It just postback the page without doing anything and I don't see the AjaxManager loading panel.

<script type="text/javascript">  function HandkeKeyPress(sender, eventArgs)  {     if (eventArgs.get_domEvent().keyCode == 13)     {        __doPostBack('Button2','');     }  }  </script> 

This executes the onclick event but generates a console error TypeError: sender.raise_SelectedIndexChanged is not a function

function ClientKeyPressingCombo(sender, eventArgs) {
                if (eventArgs.get_domEvent().keyCode == 9) { }
                else if (eventArgs.get_domEvent().keyCode == 13) {
                    sender.raise_SelectedIndexChanged();
                }
            }