When working with state management and data-fetching libraries in React applications, you might encounter an interesting behavior difference during logout flows or similar global state resets. Specifically, if you use Zustand to manage user state and React Query to manage server-side data, you might notice that resetting Zustand's state works seamlessly, but clearing React Query's cache sometimes requires extra care. This blog will explain why this happens and how to handle it properly.

A Common Logout Example

Imagine you have a logout function like this:

const onLogout = async () => {
 await logout(); // logout api
 resetUser(); // Zustand code to clear user state
 queryClient.clear(); // React Query code to clear cache
 router.push('/home'); // Navigate away
};js

At first glance, this looks fine. However, in practice, you might encounter inconsistent behavior with React Query's cache clearing, especially when navigating away (router.push()).

You might end up doing something like this instead:

const onLogout = async () => {
 await logout();
 resetUser(); // Zustand state reset
 Promise.resolve().then(() => queryClient.clear()); // React Query cache clear
 router.push('/home');
};

Why does deferring the queryClient.clear() call with Promise.resolve() sometimes work better? And why is Zustand's resetUser() always fine?

Key Difference: Zustand vs. React Query

🐻 Zustand - Simple Synchronous State Update

When you call resetUser() in Zustand, it:

1. Mutates the store state synchronously.
2. Notifies all subscribed components to re-render if necessary.
3. Ignores unmounted components since they are no longer subscribed.

🔥 React Query - Cache, Observers, and Side Effects

When you call queryClient.clear(), it:

1. Invalidates and removes query data from the cache.
2. Notifies active subscriptions (e.g. components using useQuery() hooks).
3. Handles ongoing network requests, retries, and refetches (if applicable).

The key problem is that if components are in the process of unmounting (e.g., due to router.push()) while queryClient.clear() is running, you can get into a race condition:

• Components might unsubscribe while React Query is still notifying them.
• Ongoing network requests might still resolve after you clear the cache.
• React Query hooks might still trigger updates for unmounted components.

What is a Race Condition?

A race condition happens when two or more operations happen at the same time, and the final outcome depends on the timing or order of those operations. In this case, clearing the React Query cache and unmounting components due to routing can overlap, leading to unexpected behavior or errors.

Why Deferring Works

When you do this:

Promise.resolve().then(() => queryClient.clear());

You defer the cache clearing to the next microtask. This allows React to:

1. Finish unmounting components triggered by router.push().
2. Unsubscribe any React Query observers tied to those components.
3. Safely clear the cache afterward, without interfering with ongoing React lifecycle processes.

Why Zustand Is Always Safe

Zustand's state update is synchronous and not lifecycle-sensitive:

• If you call resetUser() and a component is still mounted, it re-renders.
• If the component is unmounted, it has already unsubscribed, and nothing happens.
• There's no async behavior or network lifecycle management to interfere.

Because of this simplicity, you can reset Zustand state at any time without worrying about navigation or component lifecycles.

Summary Table

Final Thoughts

Understanding the difference between local synchronous state (Zustand) and asynchronous data-fetching state (React Query) is crucial when designing logout flows or global state resets. Zustand's simplicity allows for carefree state updates, while React Query requires more attention to lifecycle timing.

When in doubt, defer cache clearing to ensure it runs after routing transitions complete. This small adjustment can save you from subtle race conditions and improve your app's stability.

Happy coding! 🚀