Скачать или смотреть How to Properly Update State for Nested Objects in React

Learn how to handle and update nested state objects in React efficiently using the `useState` hook.
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This video is based on the question https://stackoverflow.com/q/69701561/ asked by the user 'Abdullah' ( https://stackoverflow.com/u/14888175/ ) and on the answer https://stackoverflow.com/a/69701583/ provided by the user 'Drew Reese' ( https://stackoverflow.com/u/8690857/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Solving the Challenge of Updating State in an Array of Objects in React

If you’re working with React and you encounter a scenario where you need to update the state of an object within a nested array, you may run into a couple of challenges. It can be particularly tricky when you're managing checked states for checkboxes, like toggling completion status in a to-do list. In this post, we’ll go through a common problem and its solution, breaking it down into manageable sections for clarity.

The Problem

You're trying to update a checked value (i.e., isDone) of checkboxes associated with items in your todo list. To illustrate this, consider the following initial state, which contains nested objects and arrays. The goal is to change the isDone value when a checkbox is clicked.

Here’s how your initial state looks:

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The corresponding JSX looks like this:

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However, you might find out that the function responsible for updating the state isn’t working as expected. The code for updating the state looks like this:

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When this function runs, it only updates the list of steps and does not affect the entire todoList state, which is not ideal.

The Solution

To properly update the nested state, you must ensure that you handle merging both the root state and the nested state correctly. The useState setter function allows you to pass a function to ensure you work with the most recent state. Here’s a better approach:

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Breakdown of the Solution

Shallow Copy of Root State: By spreading the current state, ...state, we create a copy of the state object, which prevents direct mutations of the state.

Shallow Copy of Foundation Object: This is needed because you want to maintain the current structure of your state. Thus, ...state.foundation ensures that other parts of the foundation object remain unchanged.

Updating Nested Steps: Using .map(), we iterate through the steps array and toggle the isDone property of the relevant step. We return either the updated step or the existing one depending on the key match.

By following this approach, you should successfully update the state of your todo list while maintaining overall state integrity.

Conclusion

Updating nested state objects within React can be challenging, but understanding how to manipulate state immutably will set you up for success. Always remember to properly manage both the root state and any nested data structures. With careful attention to detail, your React components can function correctly while providing a smooth user experience.

Now you're ready to implement more complex state updates in your applications. Happy coding!