Ниже приведен комментарий кода V8, я не совсем понимаю объяснения.
/**
* Marks the reference to this object independent. Garbage collector
* is free to ignore any object groups containing this object.
* Weak callback for an independent handle should not
* assume that it will be preceded by a global GC prologue callback
* or followed by a global GC epilogue callback.
*/
inline void MarkIndependent();
inline void MarkIndependent(Isolate* isolate);