How to Prevent setState() from Stringifying Your Array in React Native

Learn how to handle state updates correctly in React Native and prevent unwanted stringification of your arrays with `setState()`.
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How to Prevent setState() from Stringifying Your Array in React Native

When working with state management in React (or React Native), you might encounter some confusing behavior when updating state, especially if you are fetching data from an external source. A common problem developers face is when an array is unintentionally converted to a string format, which can lead to unexpected results. In this guide, we will explore a specific example of this issue and provide a solution to keep your data intact.

Understanding the Problem

Imagine you have a function, eventQuery, which fetches data from a Firebase database. You expect the data to return an array of arrays, each containing a string and an object. However, when using setState() to update your state with this data, you find that the output appears to be stringified, leading to confusion.

Here’s a breakdown of the situation:

You fetch data that should look like this:

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

Upon attempting to log the state right after setting it, the output erroneously looks like:

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

This happens even though technically, setState neither runs toString() on your data nor modifies it in this way.

Analyzing the Issue

The crux of the issue lies in the way you're logging the state. When you concatenate the existingEvents array with a string using the + , JavaScript coerces the array into a string format for that operation, leading to the stringified result you see.

Here's what went wrong:

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

The Solution

To properly view the state without coercing it to a string, you need to change how you log your array.

Step 1: Modify Your Console Log

Instead of concatenating the string with existingEvents, use a comma to pass the array as a separate argument. This way, JavaScript recognizes it as an array and outputs it as such.

Change this:

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

To this:

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

Step 2: Adjust Your Promise Chain

Additionally, there is an error in your .then() function. It should not immediately call setExistingEvents(''), as this can cause unwanted behavior. Here's how to fix it:

Before:

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

After:

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

Conclusion

By adjusting your logging method and ensuring that your .then() function is correctly structured, you can avoid the confusion that arises from unintentionally stringifying your arrays. It's crucial to handle your state updates carefully in React to maintain the integrity of your data. By following these steps, you'll be able to keep your fetched data structured and effectively manage your component's state.

Feel free to implement these changes in your project and observe how it enhances your experience with state management in React Native!