onActionProcess.js

import("system.vars");
import("system.calendars");
import("system.question");
import("system.translate");


var event = JSON.parse(vars.getString("$param.MasterEntry_param"));

if(event != undefined && event != "")
{
    var reallyDelete = question.askYesNo(translate.text("Delete appointment"), translate.text("Do you really want to delete this recurring appointment?"), false);
    if(reallyDelete)
        calendars.removeEntryByUID(-1, null, event[calendars.ID], null);
}