That's a good point. The "Internals of Nova" blog posts do a bit more explicit comparisons to V8.

In V8, and other production engines AFAIK, objects are variable-sized monoliths: All of their statically known data is contained in one slab. This means that for example in Node.js an empty ArrayBuffer is 96 bytes in size (IIRC).

Basically, they implement the ECMASCript specification defined inheritance chain using object-oriented class inheritance.