public function hasListener(string $event, string $listenerId): bool
    {
        return $this->has($event) && isset(self::$events[$event][$listenerId]);
    }
public function hasListener(string $event, string $listenerId): bool
    {
        return $this->has($event) && isset(self::$events[$event][$listenerId]);
    }
public function hasListener ( string $ event , string $ listenerId ) : bool { return $ this -> has ( $ event ) && isset ( self :: $ events [ $ event ] [ $ listenerId ] ) ; }
Determine whether an event has a specified listener.

@param string $event      The event
@param string $listenerId The event listener

@return bool
Determine whether an event has a specified listener .