Add function to check if there is a listener for an event.

source/engine/core/eventnotifier.js

@@ -14,6 +14,11 @@ export class EventNotifier
         listeners.push (listener);
     }
 
+    HasEventListener (name)
+    {
+        return this.eventListeners.has (name);
+    }
+
     NotifyEventListeners (name, ...args)
     {
         if (!this.eventListeners.has (name)) {

test/tests/core_test.js

@@ -62,6 +62,9 @@ describe ('Core', function () {
         });
         en.NotifyEventListeners ('first_event', 5);
         en.NotifyEventListeners ('second_event', 10, 15);
+        assert.ok (en.HasEventListener ('first_event'));
+        assert.ok (en.HasEventListener ('second_event'));
+        assert.ok (!en.HasEventListener ('third_event'));
         assert.strictEqual (sumValues, 90);
     });
 });