Can multiple slices modify the same part of state?

In Redux Toolkit, each slice is designed to manage its own section of the state tree. However, multiple slices can still influence the same data indirectly through shared actions or by using extraReducers.

Ways Multiple Slices Can Affect Shared State

1
If multiple slices need to react to the same action, use extraReducers in each slice to handle that shared action type.
2
Avoid directly modifying another slice’s state; instead, design global actions or thunks that trigger updates in multiple slices.
3
Keep shared state minimal to reduce coupling between features.

Example: Shared Action Across Slices

Difficulty: 5/10

Topics: slice reducers, state overlap, conflict resolution

Scenario Questions

0-2 years experience

1
Imagine you have two slices, userSlice and profileSlice, both defining reducers that update state.user.name. If you dispatch an action from profileSlice that changes state.user.name, what will happen to the value set by userSlice? How would you ensure the update works as you expect?
2
You need to add a new field isLoading to the global state, and both authSlice and dataSlice want to toggle it. How would you implement this without causing unexpected overwrites?

2-5 years experience

1
During a sprint we added a settingsSlice that also writes to state.ui.theme, which was previously managed by uiSlice. After merging, the UI sometimes flickers between themes. Walk me through how you'd debug this and what design changes you'd consider.
2
Our team noticed that when two async thunks from different slices both update state.notifications.list, the final list sometimes loses items. Explain why this can happen in RTK and how you'd restructure the slices to avoid it.

5-8 years experience

1
We have a large application with dozens of slices, and several of them need to update a shared entityCache object. Discuss the trade‑offs of letting each slice directly mutate that part of the state versus extracting a dedicated cache slice or using middleware. Include considerations for performance, testability, and future scaling.
2
Suppose you need to enforce that only one slice can modify state.session.token at a time to avoid race conditions from concurrent login/logout actions. How would you design a solution in RTK, and what patterns would you use to guarantee consistency?

8+ years experience

1
Our organization is migrating several micro‑frontends into a monorepo, each with its own Redux store. Some stores share overlapping state like currentUser. How would you architect a shared state strategy that prevents multiple slices across micro‑frontends from stepping on each other's data, while keeping the stores loosely coupled?
2
Looking ahead, we anticipate adding feature flags that many slices will read and sometimes write. What long‑term approach would you recommend for managing such cross‑cutting state in RTK to avoid slice collisions, and how would you phase it in across teams?

Follow-up Questions

❓What problems can arise if two slices independently mutate the same property?
❓How does RTK's immer integration influence the way overlapping reducers behave?
❓Can you use extraReducers or middleware to coordinate updates across slices, and when would you choose each approach?