since it is not shown while loading.

until absences page in coursebook is ready.

& use documentations instead of lesson-events

Did nothing in this case previously

& do the TODO.
Also leave a pointer how to improve it (even) more.

It does not have to be the currentDate. This holds only for the first day.

Updating the hash fragment causes a small delay while scrolling.
=> Update only after user finished scrolling.
Uses requestIdleCallback
which is not ready for prime time in Safari. But should work elsewhere.