Zustand state is cleared during Next.js deployment

[uki1014]

I have encountered an event in a production Next.js application, where the Zustand state was cleared during deployment.
At that time, the request log showed that the state managed by useState was not cleared.

Next.js seems to use the Automatic Updates mechanism to automatically modernize client-side JavaScript without reloading if the latest version exists.
(I don't understand much about the details regarding Auto updates in Next.js...)

Does this destroy objects referenced by libraries like Zustand that are running outside of React?

• version
  • Next.js: 12.3.1
  • Zustand: 4.3.9

[icyJoseph]

This sounds weird.

I guess your zustand store is setup in _app? And it gets props calculated either by gIP, or GSP, or GSSP? Then maybe when the JSON for a page is pre-fetched, and then you navigate into the page, the props that drive the zustand store get reset?

[uki1014]

so the React state is persisted, but not the Zustand store?

I assume from the following documentation that when fetching new JavaScript files after deployment, Next.js can use the official React API (e.g useState) to maintain local state, but the state of external libraries such as Zustand is cleared I assumed that the state of external libraries such as Zustand would be cleared.

https://nextjs.org/docs/architecture/fast-refresh#limitations

The tabs inside this page do not trigger URL changes right?

The URLs are the same, but queryparams are changed to express the state of switching tabs.

[icyJoseph]

Mmm but Fast Refresh is a dev mode thing, isn't it? it should impact production builds.

And how is the URL navigation done then? Via next/router or next/link in some fashion? It does say in Automatic Updates, that a next/link behaves as an a tag during Automatic Updates, but why would the React state persist 🤔 unless local storage or some other API is at play here? Puzzling

[uki1014]

@icyJoseph
We investigated and found that it was an application-side defect that occurs only under complex conditions, so this discussion is closed.
The Next.js deployment mechanism was never affected.

Thank you for your reply. 🙏

[icyJoseph]

@uki1014 ah, of course. That's what I was after initially, but at _app level.

Good that you got it!