Resolving the Cannot assign to read only property Error in Recoil with Next.js

---

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Cannot assign to read only property with .map(). Recoil with NextJs

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---

Understanding the Problem

The Error Message

The error Cannot assign to read only property indicates that you're trying to mutate (change) an object directly which is marked as immutable. In React and Recoil, state should not be mutated directly; instead, you should create new objects or arrays that represent the updated state.

Example of the Code Causing the Issue

Here's the scenario described:

You have an array of objects, allData, in your state:

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

You attempt to edit this data through a function edit like so:

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

As you've discovered, this direct assignment is problematic and leads to the aforementioned error.

The Solution: Updating State Correctly

To prevent this error, we should create a new array with the modifications we need instead of trying to change the existing state directly. Here’s how to do it:

Step-by-Step Guide

Use the map() method to create a new copy of the array.

Create a new object within the map() callback to avoid direct mutation.

Set the new state with setAllData() after making your changes.

Updated Code Implementation

Here’s how to modify your edit() function correctly:

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

Key Points

Immutable State: Always create new objects or arrays when updating state in React to ensure immutability.

Spread Operator: Use the spread operator ({...data}) to create a shallow copy of objects, which prevents direct mutation.

State Updates in Recoil: After preparing your new data structure, use setAllData() to update the state.

Conclusion