Iterating over Properties of a Proxied Object does not work

I have the need to wrap an object in a JS proxy. The proxy handler must be implemented in C++. The target "object" is empty and acts just as a dummy. More important is the functionality of the proxy to intercept property accesses and to re-route them to own logic.

When wrapping an arbitrary object in a Javascript proxy, it is not possible to iterate over the proxied properties. I see that ownKeys() is called on the handler, but no further action is taken.

Iterating over the object with a for..of loop requests Symbol.iterator which I have no idea of how to produce that in C++.