Скачать или смотреть Resolving Redux Toolkit Error: A case reducer on a non-draftable value must not return undefined

Learn how to troubleshoot and resolve the `undefined` return error in your Redux Toolkit case reducers with this comprehensive guide.
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Understanding and Resolving Redux Toolkit Error: A Case Reducer on a Non-Draftable Value Must Not Return Undefined

If you are working with Redux Toolkit, you may encounter an error that states, "A case reducer on a non-draftable value must not return undefined." This can be quite frustrating, especially if everything appears to be functioning correctly in your neighboring projects. In this guide, we will dive into this problem and provide practical solutions to fix it.

The Problem at Hand

What The Error Means

When using Redux Toolkit, reducers are meant to manage state updates. If a reducer returns undefined or does not return the updated state properly, the framework will throw the error above. This can prevent your application from correctly managing the Redux state, leading to unexpected behaviors.

Case Study

Let's look at a simplified version of what might be causing the problem. You defined a UserSlice that includes several action creators, including signIn and signInWithToken. The following is a breakdown of how you might have set up your reducer:

[[See Video to Reveal this Text or Code Snippet]]

In the example above, you are trying to change the state of the user by assigning a new value to state. However, if your case reducer does not return a new state object explicitly, it could lead to the error message you've encountered.

How to Solve the Issue

1. Return State Properly

The main takeaway from this error is that when you're dealing with state updates in reducers, you need to return the updated state explicitly. If you are using arrow functions to define your reducers, you must remember to wrap your return values in parentheses. Here's how to fix your code:

Example of Fixed Code

[[See Video to Reveal this Text or Code Snippet]]

2. Use Immutability Helpers

When updating the state, especially if you manage complex states, consider using immutability helpers such as immer or simply leveraging the spread operator to maintain immutability while updating the state.

3. Check for Non-draftable Values

Ensure that the value of the state being updated is indeed a draftable object. Primitive types (like null or string) will throw this error if a reducer tries to modify them in-place.

4. Debugging Tips

Console Logging: Add console logs before every return statement to check what the state looks like at each step.

Check Middleware: Sometimes middleware like redux-thunk or redux-saga can interfere as well. Ensure these are properly set up.

Conclusion

Troubleshooting Redux Toolkit errors like "A case reducer on a non-draftable value must not return undefined" can be daunting, but with systematic debugging and understanding reducer logic, you can effectively resolve these issues. Always ensure to return the updated state explicitly in your reducers to avoid such pitfalls.

By understanding how to return updated states correctly and leveraging the power of immutability, you can maintain clean and bug-free Redux state management in your applications. If you have further questions or encounter other errors, feel free to reach out or leave a comment below!