Solving the Issue of Cannot assign to read only property in React/Redux Toolkit

Discover how to effectively manage state updates in React and Redux Toolkit, specifically when working with nested objects and arrays. Learn the proper techniques to avoid errors and ensure smooth editing functionality.
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Solving the Issue of Cannot assign to read only property in React/Redux Toolkit

When developing applications with React and Redux Toolkit, managing state can sometimes lead to puzzling errors. A common issue that developers face is the error message: "Cannot assign to read only property 'board' of object." This typically occurs when trying to update state that is referencing an object in a way that violates immutability principles. In this guide, we'll break down this issue and provide a solution to keep your task manager app running smoothly.

Understanding the Problem

In our scenario, we are building a task manager application using Redux Toolkit for state management. The application contains a structure where each board has a name and an array of columns. When attempting to edit the properties of the columns, developers may encounter errors because they are trying to mutate the state directly instead of following React's best practices.

Here’s a summary of what leads to the problem:

State Setup: The columns state is initiated using a shallow copy of the activeBoard's columns array. However, the individual elements within that array are still references to the original objects in the Redux state store.

Mutation Issue: When trying to update the columns, the code attempts to directly mutate the properties of these referenced elements, leading to the error.

How to Solve the Issue

To solve this issue effectively, we need to ensure that we correctly manage immutability by creating new object references during updates. Here’s how to do this step by step:

Step 1: Create a New Array with Updated Elements

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

Step 2: Updating State Correctly

In the above example, when the columnsChangeHandler is triggered:

We extract the name and value from the event target.

We update the state with setColumns, where we call map on the existing columns array:

If the current index matches the index of the column being edited (index === i), we create a new object that merges existing properties with the updated value.

If the index does not match, we return the existing element, preserving immutability.

Conclusion

By following the steps outlined above, you can effectively fix the error and ensure that your application adheres to the principles of immutability and state management in React and Redux Toolkit. This adjustment not only resolves the immediate issue but also sets a solid foundation for further development within your application.

Remember, whenever you're updating nested state in React, it's crucial to create new copies of both arrays and their elements to prevent unexpected behaviors.

With this knowledge, you can confidently navigate state updates in your task manager app, avoiding the common pitfalls that arise in React/Redux Toolkit applications.

Happy coding!