It's about trying to understand the architecture behind how updates to web application is done.
I've been working on a non-public website that has bunch of records displayed in a UI, now the intelligent part of this application is that if I delete something in the database through API's without touching any button within the UI, the UI automatically takes it off the list.
If there's an upload of a file in progress, I see progress bar with percentage, any changes in the metadata behind the scenes I see it reflected immediately, it's like it's fully wired with the changes one the backend database.
We have something similar in our mail applications too, for instance gmail, if a mail arrives, automatically a record gets added without the refresh.
The question, how the UI knows that something changed in the backend, are there any connected sockets sending data back and forth, or are there continuous ajax calls (doesn't seem efficient).
Basically the gist is, how the UI synchronizes itself with the changes on the backend.