Fixing Tanstack Query Null Error Handling with Expo and React Native

Using Tanstack Query in Expo with React Native: Debugging Null Error Responses

Debugging errors in React Native can be tricky, especially when working with complex data-fetching libraries like Tanstack Query. Recently, while setting up Tanstack Query for a new Expo project, I noticed that my `error` object returned as `null` even when an error was thrown in the query function. This issue seemed puzzling, especially as I’d configured the queryFn to explicitly throw an error.

One of the main challenges in this case stemmed from React Query's handling of asynchronous errors in the Expo-managed environment, particularly in projects structured around an app directory rather than a single App.tsx entry point. This approach, though convenient for organizing larger codebases, can add unexpected complexity when it comes to error handling.

Since the Tanstack Query setup is a popular choice for React Native developers who value seamless data management, figuring out why the error was consistently null was key to ensuring the app's stability. After all, reliable error feedback is essential for delivering responsive and user-friendly applications.

In this guide, I'll walk through the code, explain where the issue arises, and suggest some solutions. By the end, you'll have clearer insights into debugging and handling errors effectively in Tanstack Query with Expo and React Native. 🚀

Understanding Error Handling in Tanstack Query with React Native and Expo

In the example scripts above, the main focus is on using Tanstack Query in a React Native Expo environment to manage errors effectively. The first script demonstrates a basic implementation of the useQuery hook, which fetches data or throws an error based on a specified condition. This example is key for developers who need error feedback directly in their UI, as useQuery provides a controlled way to handle asynchronous calls. However, a unique challenge here is that even when an error is intentionally thrown in the query function, the error object is returned as null. This is a known issue in environments like Expo, where async states can sometimes delay or alter expected error behaviors.

To resolve this, the second example script introduces the onError callback within Tanstack Query’s defaultOptions. Here, a QueryClient is created with specific options for error handling, which globally logs any errors encountered during the query. This approach allows you to centralize error tracking, making it easy to diagnose problems without disrupting the app's flow. Using the onError callback is beneficial because it provides a safety net for unhandled errors, offering consistent error feedback to developers even if the error state is misrepresented in the UI. This is especially helpful for debugging, as you can log errors directly to the console, providing a clear trail of issues.

The third script goes further by adding unit tests using Jest and Testing Library to ensure that the error handling is functioning as expected. Here, the test looks for the presence of an error message rendered in the component, simulating a real user experience where errors should be visible in the UI. This method of unit testing makes sure that, regardless of environment-specific behaviors, the component reliably renders error states. Running these tests helps identify whether the error display issues are related to Tanstack Query, Expo, or another aspect of the app. Testing frameworks like Jest help validate that our components handle errors as expected, even in complex async contexts.

In practice, these scripts help developers manage and display errors consistently in Expo apps. For instance, if a network error occurs, users will see a clear message in the UI instead of a blank screen or silent failure. This is crucial in mobile applications where real-time feedback enhances user trust. By implementing global error handling with QueryClientProvider and verifying UI elements in Jest, developers gain confidence that users will receive feedback when an error happens, rather than experiencing an unpredictable app state. These methods are not just technical but also practical, as they help avoid common pitfalls of asynchronous data handling in mobile environments. 📱

// Approach 1: Basic Error Handling with useQuery and try-catch block
import { KeyboardAvoidingView, Text } from 'react-native';
import { useQuery } from '@tanstack/react-query';
export default function Login() {
  const query = useQuery({
    queryKey: ['test'],
    queryFn: async () => {
      try {
        throw new Error('test error');
      } catch (error) {
        throw new Error(error.message);
      }
    }
  });
  if (query.isError) {
    return (
      <KeyboardAvoidingView behavior="padding">
        <Text>{query.error?.message || 'Unknown error'}</Text>
      </KeyboardAvoidingView>
    );
  }
  return (
    <KeyboardAvoidingView behavior="padding">
      <Text>Success</Text>
    </KeyboardAvoidingView>
  );
}

import { KeyboardAvoidingView, Text } from 'react-native';
import { useQuery, QueryClient, QueryClientProvider } from '@tanstack/react-query';
const queryClient = new QueryClient({
  defaultOptions: {
    queries: {
      onError: (error) => {
        console.error('Query error:', error);
      },
    },
  }
});
export default function AppWrapper() {
  return (
    <QueryClientProvider client={queryClient}>
      <Login />
    </QueryClientProvider>
  );
}
function Login() {
  const query = useQuery({
    queryKey: ['test'],
    queryFn: async () => {
      throw new Error('Test error');
    },
    onError: (error) => {
      console.log('Query-level error:', error.message);
    }
  });
  if (query.isError) {
    return (
      <KeyboardAvoidingView behavior="padding">
        <Text>{query.error?.message}</Text>
      </KeyboardAvoidingView>
    );
  }
  return (
    <KeyboardAvoidingView behavior="padding">
      <Text>Success</Text>
    </KeyboardAvoidingView>
  );
}

import { render, screen } from '@testing-library/react-native';
import Login from './Login';
import { QueryClient, QueryClientProvider } from '@tanstack/react-query';
test('renders error message on failed query', async () => {
  const queryClient = new QueryClient();
  render(
    <QueryClientProvider client={queryClient}>
      <Login />
    </QueryClientProvider>
  );
  await screen.findByText(/test error/i);
  expect(screen.getByText('test error')).toBeTruthy();
});

Advanced Error Handling Techniques with Tanstack Query in Expo

In Expo and React Native applications, handling asynchronous data with Tanstack Query requires careful error handling, especially when working with custom app structures. A key part of this setup involves configuring error-handling options in QueryClientProvider to ensure consistent error feedback across components. By setting up a QueryClient with customized options like onError, developers can log errors in one centralized location, improving app maintainability. This approach is especially useful for larger applications, where debugging each screen or component individually would be time-consuming.

For example, enabling the failureReason attribute in Tanstack Query can help diagnose persistent error cases. It holds the error object details, even if the main error attribute appears as null in the console. This additional data can assist in pinpointing which part of the query caused the error, making it easier to address backend or API-specific issues. Adding detailed logging like this is an essential step for applications that frequently interact with remote data, as it provides a clearer view of potential points of failure. 📲

Another technique to consider is using error boundaries around specific components. This allows you to catch unhandled errors and display customized feedback for users. For instance, an error boundary can display a message indicating connectivity issues when a network error occurs. This helps prevent blank screens and guides users to take actions, like retrying or checking their connection. When combined with Tanstack Query’s error handling, error boundaries create a seamless user experience, turning technical errors into user-friendly feedback. Leveraging these strategies can significantly improve reliability and maintain user trust in data-driven apps.