Fixing the Uncaught TypeError in Your Redux Todo App

Описание: Discover how to resolve the Redux error "Cannot read properties of undefined" when building a ReactJS todo app, with clear explanations and examples.
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This video is based on the question https://stackoverflow.com/q/76697773/ asked by the user 'Shadq' ( https://stackoverflow.com/u/14302886/ ) and on the answer https://stackoverflow.com/a/76698456/ provided by the user 'Shadq' ( https://stackoverflow.com/u/14302886/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Fixing the Uncaught TypeError in Your Redux Todo App: A Simple Guide

Building a todo app using React and Redux is a great way to learn modern web development. However, it's not uncommon to hit some snags along the way. One of the most frustrating errors you may encounter is "Uncaught TypeError: Cannot read properties of undefined (reading 'list')". Let's break down this error, why it occurs, and how to fix it.

Understanding the Problem

When working with Redux state management, developers often need to access specific parts of the application's state. In your case, the error arises from trying to access the list property of the todos slice in your Redux store. Here's the problem in a nutshell:

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Why the Error?

The error indicates that JavaScript is attempting to read the list property from an undefined state. This usually means there is a mismatch between how the store is set up and how it's being accessed. In your case, your slice is defined as todo, not todos, causing the problem.

The Solution

Step 1: Check Your store.js Configuration

In your store.js, you configured the reducer like this:

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Here, you named the slice todo.

Step 2: Correct the Selector Function

Your selector function tries to access state.todos.list, which does not exist as per your store setup. To fix this, simply update the selector to use the correct name:

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Step 3: Ensure Consistency Across Your Components

Ensure that your component file App.jsx, which uses the selector to retrieve todos, reflects the changes correctly. The updated useSelector call should now work without throwing an error:

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Example of a Corrected Store Configuration

Here’s how your corrected reducer setup should look:

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Conclusion

By carefully aligning your slice name in the Redux store with how you access it in your components, you can resolve the Uncaught TypeError. This small oversight can cause significant frustration, but it’s easily fixable with a few tweaks. Now you're back on track, and your todo app will function as intended!

If you have further questions or need additional assistance with React or Redux, feel free to reach out. Happy coding!