What are actions in Redux Toolkit?

In Redux, actions are plain JavaScript objects that describe what event has occurred and how the state should change. Each action must have a type field, and optionally, a payload that carries additional data.

Key Points About Actions

1
Actions are automatically created for each reducer defined inside createSlice().
2
Each action’s type is generated by combining the slice name and reducer name (e.g., counter/increment).
3
Actions can be dispatched to trigger state updates through reducers or extraReducers.

Example: Auto-Generated Actions in Redux Toolkit

Difficulty: 3/10

Topics: createSlice, action creators, reducer logic

Scenario Questions

0-2 years experience

1
You're adding a toggle feature for a dark mode switch using Redux Toolkit — how would you define and dispatch the action to flip the theme state?
2
If you forget to export the action creator from your createSlice and try to use it in a component, what error would you see and why?
3
You dispatch an action but the state doesn’t update — what are the two most likely reasons related to actions or reducers?

2-5 years experience

1
A feature that updates user preferences breaks after a refactor — the action is dispatched, but the reducer isn’t handling it. How would you debug whether the issue is with the action payload, type mismatch, or reducer logic?
2
Your team is splitting a large slice into smaller ones — how do you ensure actions from one slice don’t accidentally trigger reducers in another, and what’s the safest way to handle cross-slice communication?
3
You notice that some actions are being dispatched too frequently, causing unnecessary re-renders. How would you trace whether it’s the action dispatch frequency or the selector logic causing the issue?

5-8 years experience

1
You’re designing a high-frequency real-time dashboard that dispatches 50+ actions per second — how do you evaluate whether using createSlice-generated actions introduces performance bottlenecks, and what alternatives would you consider?
2
In a legacy app, you’re migrating from vanilla Redux to RTK. Some actions are dispatched from third-party libraries that expect string types — how do you make RTK actions compatible without breaking existing code?
3
How would you structure actions and reducers to support undo/redo across multiple slices without creating a monolithic state or duplicating logic?

8+ years experience

1
You’re leading a migration from a custom state management system to RTK across 15+ teams — how do you standardize action naming, payload structure, and middleware usage to avoid fragmentation and ensure long-term maintainability?
2
A critical feature relies on actions being dispatched across micro-frontends. How would you design a contract for RTK actions that ensures type safety, backward compatibility, and zero-runtime coupling between independently deployed apps?
3
RTK actions are serialized for logging and replay. What edge cases in action payloads (e.g., functions, circular refs, Symbols) could break devtools or persistence, and how would you enforce safe serialization at the architecture level?

Follow-up Questions

❓How do you know if an action was dispatched successfully?
❓What happens if you dispatch an action that doesn’t match any reducer?
❓Can you manually create an action without createSlice?