Svelte: setting count does not re-render correctly

[nordfjord]

Describe the bug

The virtual list is not updated after setting the count option

Your minimal, reproducible example

https://svelte.dev/playground/61de6ef02eee43088d2ee0482cbe21d3?version=5.25.3

Steps to reproduce

given a scroll area larger than the list it includes
when count is updated
then nothing happens.

Expected behavior

I would've expected the list to rerender with the updated count, showing new items.

This seems to be resolved by calling $virtualizer.measure() after the setOptions call.

How often does this bug happen?

Every time

Screenshots or Videos

No response

Platform

MacOS, Chromium

tanstack-virtual version

v3.13.5

TypeScript version

No response

Additional context

No response

Terms & Code of Conduct

• I agree to follow this project's Code of Conduct
• I understand that if my bug cannot be reliable reproduced in a debuggable environment, it will probably not be fixed and this issue may even be closed.

[shniubobo]

This may be related to #363.

I have observed the same bug with @tanstack/vue-virtual@3.13.6. Wrapping useVirtualizer within computed to work around this.

[abbeyperini]

This is also happening in @tanstack/vue-virtual v3.13.12. If the setting is coming from a computed prop, to get the rows to load, you have to either wrap useVirtualizer in a computed (which causes many unnecessary re-renders) or manually call setOptions in a watch.