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Finally reviewing this, sorry it took so long.

I personally don't like having to call getPrototypeOf every time because it's slow, but we have a test that relies on this behavior.

This is covered by the constantSuper assumption, right?

Can you add a test for the execution order between property access and arguments evaluation?

let argsEval = false;
let err = {};

class A {
  get x() { throw {} }
}

class B extends A {
  method() {
    super.x(argsEval = true);
  }
}

expect(() => new B().method()).toThrow(err);
expect(argsEval).toBe(false);