Receive only added documents

[DooDiddle]

Hello,

I'd like to be able to receive an update only if a point has entered my radius. In other words, if an item has exited, position has changed, or has been deleted, I don't want to get an update event for that. In addition, I only want to receive those items that have entered, not the whole list of items. Right now, I tried something like the examples:
points.subscribe(x => {console.log(x)})
But here x gives me the entire list every time anything changed. How can I
1-) receive an update only if an item has entered
2-) get a list of only those items that have entered.

Thank you