reviewed: Summary: Fixes the virtualized select list "losing" options during large scrolls (#5340). The root cause was that VirtualizedItemList.getVisibleRange() computed the visible window using a fixed 40px row height, while the actual DOM positioning (getTotalHeight() / getOffsetTop()) used variable heights via getVirtualItemHeight(). On lists with taller rows (items with instructions), the two drifted apart and the rendered slice no longer matched where items were placed — producing blank gaps / vanishing options on long scrolls.

Verdict: Approve. The fix is correct and well-scoped.

What's good
getVisibleRange() now walks actual item heights, making it consistent with getTotalHeight()/getOffsetTop(). This is the right fix for the reported bug.
virtualizationHeight is now properly forwarded into , so containerHeight honors the configured height instead of being hard-locked at 400.
Sensible defensive additions: the if (!item) return 40 guard in getVirtualItemHeight() and the empty-list early return in getVisibleRange().
The .es6 source and the hand-maintained .js artifact were updated consistently.

Minor (non-blocking)
In the end-of-range loop, visibleHeight accumulates from the top of startIndex rather than from scrollTop. Since the first item's top usually sits slightly above the viewport, the bottom can be under-counted by up to one row. The overscan of 10 comfortably absorbs this in practice, so no change required — just noting it.
select_list.js appears to be hand-maintained alongside select_list.es6 (no gulp step compiles it). Worth confirming that's the intended workflow so the two don't diverge in future edits.

checked
from my side it's ready to approve

@robinsowell if it works for you as well left comment and I'll approve it
Thanks