The pattern A extends B is commonly (would say 70% of usage) implemented in the following way:
A.prototype.__proto__ = B.prototype;

As we know, in nashorn this has no effect.

We are rewriting it as (using node 'util' module) : require("util").inherits(A, B);
We are also restructuring some code to only create instance after the prototype has been fully defined.

This imply a lot of patching.

Having an option to enable writable proto would help run existing scripts unmodified.