Solving the TypeError: Cannot read from private field in Tanstack React Query

Discover effective solutions for dealing with the `TypeError` in Tanstack Query, especially when using `invalidateQueries`. This guide provides insights and best practices for React developers.
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Understanding the TypeError with Tanstack React Query

When working on a project utilizing Tanstack Query V5 in your React application, you may encounter the frustrating error message: TypeError: Cannot read from private field. This error could pop up when you try to use the invalidateQueries function. If you are facing this issue while trying to trigger a refetch of your invoice list after a mutation (like an invoice deletion), you're not alone. This post seeks to break down the reason behind this error and offer a straightforward solution.

The Problem

In your case, you're encountering the error as a response to your attempt to use the invalidateQueries method. Here’s a brief refresh on the context of your setup:

You are using Tanstack Query V5 in a Vite + React project.

The trigger for the error arises when calling invalidateQueries in the success callback of your useMutation.

Error Example:

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

This issue can be traced back to the way you're accessing the invalidateQueries function from the queryClient.

The Technical Explanation

The crux of the issue lies in the way JavaScript handles scope and context, especially when it comes to class fields that are marked as private. In Tanstack Query, the QueryClient class has private fields, which makes accessing them outside their defined context impossible.

What Happens When You Destructure?

When you do something like this:

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

You lose the reference to the original queryClient context. Although you have a reference to the function itself, it doesn't have access to the private fields it relies on. This wilful loss of context causes the error when invoking invalidateQueries().

Expected Behavior

Here’s how it should work:

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

The Solution

To resolve this issue, it’s important to avoid destructuring the queryClient. Instead, directly use the queryClient instance returned by useQueryClient.

Here’s how to do it right:

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

Using the above approach ensures that invalidateQueries() has access to the correct context, eliminating the error.

Conclusion

If you find yourself grappling with the TypeError: Cannot read from private field while using invalidateQueries in Tanstack Query, remember that proper context is key. Always keep your queryClient instance intact without destructuring it. This will help you avoid headaches down the line and keep your code running smoothly.

If you're still facing issues or have further questions on using Tanstack Query effectively, feel free to drop your thoughts in the comments below!