For display on the map itself. This is as far as I got: There is no error, but also no window... The alert message in the constructor is shown so the window is created. Also the update method is never called. Also I suppose that I have to dispose or close the window in Scene_Map.prototype.terminate to prevent memory leaks? But I think windows don't update themselves. Meaning I probably have to alias the update method in the scenemanager and make it update my window.