I’m sorry, I forgot to mention that my example refers to a Row_CustomAction scenario.
I actually put code in Page_Load server event to display a button ($this->CustomActions[“star”] = new ListAction(“star”, “Add Star”, IsLoggedIn(), ACTION_POSTBACK, ACTION_MULTIPLE, “Add Star to selected records?”, “fas fa-star ew-icon”)
and code in Row_CustomAction server event (as showed in the help file).
This causes my project to trigger the Client script Form_CustomValidate event.
(I put a simple alert on top of the Form_CustomValidate client script, and the pop-up appears right after “Add Star to selected records?” confirmation pop-up is showed.)