public void foreach_member (ObjectForeach func)
Iterates over all members of this and calls
func on each one of them.
It is safe to change the value of a member of the oobject from within the iterator function, but it is not safe to add or remove members from the object.
The order in which the object members are iterated is the insertion order.
a JSON object
the function to be called on each member
data to be passed to the function