Question: Auto-scroll occurs when scrolling upward while items are dynamically appended

[tsujimic]

I'm building a chat-like UI where answers to a question are appended dynamically and displayed using Virtualizer.

While the content is still being appended, if I scroll in the opposite direction (upwards), the scroll position automatically jumps back toward the forward direction (downwards).

It's difficult to explain clearly in words, so I’ve attached a video showing the behavior.

Because the item sizes are not finalized while the data is still increasing, I suspect this might be a difficult problem to solve. However, I wanted to ask:

Is there a recommended way to handle this behavior?
Any advice or guidance would be greatly appreciated.

virtua-negative-scroll-direction.mp4

Platform

• OS: macOS
• Browser: Chrome
• Version of this package: 0.48.6
• Framework: Next.js 16.1.6

[inokawa]

I think it's not the default behavior of Virtualizer. I guess the props passed or methods used might be the cause.

Could you provide the actual code around Virtualizer?

[tsujimic]

I have shared a GitHub repository containing the code around the Virtualizer.
Could you please take a look?

https://github.com/tsujimic/virtua-app

You can reproduce the issue by clicking the "Add 1" button in the app included in the repository.

[inokawa]

Thanks! I checked the repo and I found a few things:

1. Probably this behavior is related to Jump when partially offscreen item animates to height of zero for removal #417 , in short virtua may miscalculate the position of items at the edge while scrolling.
2. Virtua doesn't support padding at scrollable element. pt-2 is very small value, but it can miscalculate scrollTop by about 7px. (Overflow content in virtualized items gets clipped #800 (comment) )

I'll try to fix #417 again.

[tsujimic]

Thanks for checking the repository and for the explanation.
I really appreciate it.

[inokawa]

Could you try 0.48.7? I think it's improved a lot, and the behavior was a different issue than #417.

[inokawa]

Improved again in 0.48.8.

[tsujimic]

Thank you for your replies. I will try it with version 0.48.8 and check.