After many searches I finally found this stackoverflow post:
And in particular:
This looked like a very nice approach.
The new thing for me was the D.call(this) idea.
( This solved the problem with the shared matrix attribute from my Spatial class in Spatial child classes.)
This led me to:
With this information I realized that there was a slight draw back with the new approach:
The class constructors were being called twice.
Once: D.call(this); and again: new D();
This led me to Object.create:
To learn about the difference between new and Object.create I read this:
But the answer in the second link was not accurate as one commenter pointed out. He had a link to the EcmaScript 5 specification: http://es5.github.com/#x18.104.22.168
This made it finally clear and I started to understand these lines in some inheritance examples:
Child.prototype = Object.create(Parent.prototype);
This basically avoids the unneeded call to the constructor.
Here is a complete example: