humanspeak / svelte-virtual-list / 28669838189

71%

main: 72%

push

github

fix(virtual-list): react to container resizes; retire the dead initialized flag (#421)

* test(virtual-list): add failing spec for ignored container resizes (#416)

Fixture at /tests/issues/issue-416 with live red/green stats: settle a
500-item list at 300px, grow the container to 900px, wait well past
ResizeObserver latency, then measure coverage (viewport height minus
the union of rendered item rects). bufferSize=2 keeps the probe honest
— the default 20-item buffer masks ~800px of missed growth. The
container behind the items is warning-red, so the unfilled region the
bug paints is visible at a glance.

Pre-fix: the grow sanity passes (clientHeight=900) and coverage reads
blankPx=460 — the render window stays sized for the stale 300px height
because the container ResizeObserver handler early-returns on the
never-set initialized flag.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(virtual-list): react to container resizes; retire the never-set initialized flag

Fixes #416

The container ResizeObserver handler early-returned unless
heightManager.initialized was true — and that flag's only writer was a
setter passed to utilsUpdateHeightAndScroll, which never called it. It
was false for the lifetime of every instance, so container resizes were
silently dropped: the internal viewport height was read once shortly
after mount, and growing the container painted an unfilled region
(fixture: 460 blank px of a 300→900px growth with a small buffer).

The resize path is now a direct syncContainerHeight() — the same
container-rect read the run-once effect and onMount already perform,
shared as one helper — with no readiness gate beyond isReady. All other
component-side consumers of the flag are gone:

- the infinite-scroll insufficientItems branch is deleted as provably
  redundant rather than revived: with items.length < loadMoreThreshold
  the atLoadingEdge comparison (range.end >= items.length - threshold)
  is against a negative number, so sh... (continued)

349 of 555 branches covered (62.88%)

Branch coverage included in aggregate %.

41 of 47 new or added lines in 4 files covered. (87.23%)

702 of 928 relevant lines covered (75.65%)

476.62 hits per line