The behavior is the same, but they are not the same thing, in the first sample it's creating a function for each and every object created (waste of memory), while in the second it's adding the function to the prototype, thus one function is being 'shared' by every object.

I might be incorrect, but I believe these 2 are the same thing?

I think you solved the exercise as intendid.

I was a bit consfused by this at first but after some exploring I think I get it now.

When you did
HumanSkin.prototype = new Cylon()
You created a property for all new HumanSkins called model. But since you never passed a model to
the new Cylon() you were inheriting from, model was left as undefined. Therefor you had to define a model of your own
within HumanSkin.

I hope that makes sense. Anybody, please correct me if I'm wrong.