Not triggering "onChange" when "visibilityRect" changes

Instead of using "isVisible", we're using "visibilityRect" to know whether the scroll is past one menu so that we can make it sticky, exactly like this: https://codepen.io/senff/pen/ayGvD. The problem is that *onChange* is not triggered whenever "visibilityRect" changes.

1. Should it trigger *onChange* anyway, even though "isVisible" hasn't changed? If so, should it be optional?
1. Should we have an extra callback?
1. Should it update the state with the new "visibilityRect" so that we can get it using a function as children?

Apart from that, the docs need to be updated in order to reflect that "visibilityRect" is passed to *onChange*.