virtua/svelte: onscroll does not differentiate between vertical and horizontal scroll event

[Karakatiza666]

When using VList for a vertical list, when doing horizontal scroll onscroll callback is fired with effectively scrollTop value. Ideally, either

• the onscroll callback would provide {scrollLeft: number, scrollTop: number, deltaX: number, deltaY: number}, or
• expose onscrollx and onscrolly callbacks that each have (offset: number, delta: number)

[inokawa]

It was not exposed because it's not related to virtualization and accessing scrollTop/scrollLeft excessively can degrade perf.

If you want scrollLeft while vertical scrolling, use Virtualizer, like:

<div style="overflow: auto; width:XXpx; height:XXpx" onscroll={(e)=>{ e.target.scrollLeft /* access scrollLeft*/ }}>
  <Virtualzer>
    ...
  </Virtualizer>
</div>

[Karakatiza666]

I''ll try Virtualizer, thanks! My main goal is to run some code on vertical scroll, but not horizontal scroll

[Karakatiza666]

@inokawa still, it is confusing that when you use vertical VList and do a horizontal scroll onscroll still gets called with scrollTop value, so you cannot differentiate between vertical and horizontal scrolls

[inokawa]

Thanks for the feedback. I updated the docs a bit.