First Im really not familliar with javascript, got several years of object modeling and C++ dev, but I'm a complete beginner in js... So excuse me if I'm completly out of bound...

Looking at your inheritance model, I feel like there are some oddities :
For example ObjectEntity extends AnimationSheet extends AnimatedSpriteObject extends SpriteObject extends Rect extends Object

I thinkk it should be something like that :
ObjectEntity is composed with AnimatedSpriteobject and entity related data
AnimatedSpriteobject extends SpriteObect and is composed with AnimationSheet
SpriteObject extends Rect
Rect extends Object

That may just sound like purist gibberish though...