[BUG] startReached and endReached called in succession

Describe the bug In a particular scenario,startReached and endReached called in succession.

Reproduction https://codesandbox.io/s/romantic-mountain-tzfbw

To Reproduce Steps to reproduce the behavior:

1. once initial items are loaded, scroll up to fetch previous items
2. observe the console logs

Expected behavior only startReached should be called.

Additional context This issue isn’t happening if I fetch the next items first and then scroll up to fetch previous items.

[petyosi]

I examined the linked example in further detail, and this is going to be quite hard to fix on the lib side. Let me explain:

When scrolling up and new items are prepended, the lib scrolls down first in order to compensate for the newly introduced content. When items are prepended, the browser shifts back to where the list should be.

In your case, however, the initial amount of items is small, and the scroll-down action reaches the bottom of the list. It is fairly easy to avoid that - you need to bump the amount of the initially loaded items.

On a side note, you are also using negative values for the firstItemIndex - which causes some internal calculation issues. Start from a really large item instead.

I will keep this bug open for now, but again, fixing it is going to be quite hard (I need to detect that scrolling and ignore the end reached).

[petyosi]

Nah, got it. I was not reading your report correctly