Questions
18 of 18
11. What is a thunk in Redux?
22. What is the difference between redux-thunk and createAsyncThunk?
33. How does createAsyncThunk simplify async actions?
44. What are the lifecycle actions automatically created by createAsyncThunk?
55. How do you handle pending, fulfilled, and rejected states in slices?
66. What are the advantages of using createAsyncThunk over manual thunks?
77. How do you pass parameters to a thunk function?
88. How do you handle API errors inside a thunk?
99. How can you cancel a running thunk or API call?
1010. How can you chain multiple async thunks?
1111. How can you use getState and dispatch inside a thunk?
1212. How do you use thunks in combination with RTK Query?
1313. How do you test thunks and async actions?
1414. What are best practices for organizing async logic with thunks?
1515. How do you dispatch a thunk from a React component using hooks?
1616. How do you manage loading indicators with thunks?
1717. What’s the performance implication of using too many thunks?
1818. How can you refactor thunk-based APIs to RTK Query-based APIs?
RTKRTK
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Slice
Actions
Reducers
RTK Query
Store
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Scenario Based
18 / 18

18. How can you refactor thunk-based APIs to RTK Query-based APIs?

Difficulty: 6/10
RTK Query migration, cache management, optimistic updates

Refactoring Thunk-Based APIs to RTK Query in Redux Toolkit

RTK Query simplifies data fetching and caching compared to manually managing async thunks. When refactoring from thunk-based APIs, you can move API logic from slices and thunks into createApi endpoints, which automatically generate hooks and handle caching, re-fetching, and status management.

Steps to Refactor Thunks to RTK Query
  1. 1

    1. Identify Thunk Logic: Locate existing createAsyncThunk calls that perform API requests and return fetched data.

  2. 2

    2. Create an API Slice: Replace thunk logic with createApi and define endpoints using builder.query() or builder.mutation().

  3. 3

    3. Remove Manual Status Handling: Eliminate pending, fulfilled, and rejected reducers—RTK Query automatically manages loading and error states.

  4. 4

    4. Use Auto-Generated Hooks: Replace manual dispatch and selectors with RTK Query hooks like useGetUsersQuery() or useAddUserMutation().

  5. 5

    5. Delete Redundant Slice Code: Remove async reducers and state properties that are now managed by RTK Query.

Before: Thunk-Based Example
After: RTK Query-Based Example

By migrating from thunks to RTK Query, you reduce boilerplate, simplify async logic, and gain built-in caching, invalidation, and automatic re-fetching for a more efficient and maintainable Redux architecture.

Scenario Questions

0-2 years experience

  1. 1We have a simple Redux slice that uses createAsyncThunk to fetch a list of products. How would you replace that thunk with an RTK Query endpoint?
  2. 2If you convert a thunk that returns a promise into an RTK Query query, what changes do you need to make to the component that dispatches it?

2-5 years experience

  1. 1During a feature rollout, you switched a user‑profile fetch from a thunk to RTK Query, but the UI stopped updating after a refresh. What could be causing this and how would you debug it?
  2. 2When refactoring multiple related thunks (fetch, create, delete) into a single RTK Query service, what trade‑offs do you consider regarding cache invalidation and optimistic updates?

5-8 years experience

  1. 1At scale, how does moving from thunk‑based data fetching to RTK Query affect network traffic and cache consistency across tabs, and what patterns would you use to mitigate any issues?
  2. 2Design a migration plan for a large codebase that mixes thunks and RTK Query, ensuring minimal disruption to existing features and tests.

8+ years experience

  1. 1From an architecture perspective, what are the long‑term maintenance implications of standardizing on RTK Query for all data fetching versus keeping a hybrid thunk/RTK Query approach?
  2. 2How would you convince multiple product teams to adopt RTK Query for new services, addressing concerns about learning curve, testing strategy, and backward compatibility?

Follow-up Questions

  • What steps would you take to verify that the new RTK Query endpoint works correctly?
  • How do you handle error handling differences between thunks and RTK Query?
  • Can you describe how you would monitor performance after the migration?
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