Is all you wrote here cited from that book, or just the first paragraph? Anyway,
I was aware of the fact that an array  is condidered to be a first-class Object,
BUT the class  Object doesn't have the property length. That's my point.

Is your third paragraph (that begins with "length" is a property...) also cited
from that book? If so, I will be satisfied with that answer. If not, how do you
know it?