How do you free a wrapped C++ object when associated Javascript object is garbage collected in V8?

Question

V8\'s documentation explains how to create a Javascript object that wraps a C++ object. The Javascript object holds on to a pointer to a C++ object instance. My question is, let

Answer 1

The trick is to create a Persistent handle (second bullet point from the linked-to API reference: "Persistent handles are not held on a stack and are deleted only when you specifically remove them. ... Use a persistent handle when you need to keep a reference to an object for more than one function call, or when handle lifetimes do not correspond to C++ scopes."), and call MakeWeak() on it, passing a callback function that will do the necessary cleanup ("A persistent handle can be made weak, using Persistent::MakeWeak, to trigger a callback from the garbage collector when the only references to an object are from weak persistent handles." -- that is, when all "regular" handles have gone out of scope and when the garbage collector is about to delete the object).

The Persistent::MakeWeak method signature is:

void MakeWeak(void* parameters, WeakReferenceCallback callback);

Where WeakReferenceCallback is defined as a pointer-to-function taking two parameters:

typedef void (*WeakReferenceCallback)(Persistent