StreamSubscription<Event> addEventListener(String eventType, EventListener eventListener, {
 bool useCapture: false, int priority: 0 }) {

 return this.on(eventType)._subscribe(eventListener, useCapture, priority);
}

void dispatchEvent(Event event) {
 _dispatchEventInternal(event, this, EventPhase.AT_TARGET);
}

bool hasEventListener(String eventType) {

 var eventStreams = _eventStreams;
 if (eventStreams == null) return false;
 var eventStream = eventStreams[eventType];
 if (eventStream == null) return false;

 return eventStream.hasSubscriptions;
}

EventStream<Event> on(String eventType) {

 var eventStreams = _eventStreams;
 if (eventStreams == null) {
   eventStreams = new Map<String, EventStream>();
   _eventStreams = eventStreams;
 }

 var eventStream = eventStreams[eventType];
 if (eventStream == null) {
   eventStream = new EventStream._internal(this, eventType);
   eventStreams[eventType] = eventStream;
 }

 return eventStream;
}

void removeEventListener(String eventType, EventListener eventListener, {
 bool useCapture: false }) {

 this.on(eventType)._unsubscribe(eventListener, useCapture);
}

void removeEventListeners(String eventType) {
 this.on(eventType).cancelSubscriptions();
}