on method
Implementation
void on(eventName, EventCallback f) {
if (eventName == null || f == null) return;
_emap[eventName] ??= <EventCallback>[];
_emap[eventName]!.add(f);
}
void on(eventName, EventCallback f) {
if (eventName == null || f == null) return;
_emap[eventName] ??= <EventCallback>[];
_emap[eventName]!.add(f);
}