GObject.WeakNotify

function onWeakNotify(data: void, where_the_object_was: GObject.Object): void {
}
  

A GObject.WeakNotify function can be added to an object as a callback that gets triggered when the object is finalized. Since the object is already being finalized when the GObject.WeakNotify is called, there's not much you could do with the object, apart from e.g. using its address as hash-index or the like.