React Query is a popular library for fetching and caching data in React applications. It's designed to work with APIs and handle network requests in a way that makes it easy for developers to build scalable and fast web applications. But sometimes things don't go as planned, and unexpected bugs can arise. In this post, we'll take a look at a common issue that can occur when using React Query and show you how to debug and solve it.

The Problem

Imagine you have a React component that uses React Query to fetch data from an API and display it. You're getting the data for page 2 of the API, but for page 3, the data is missing. In the network tab of your browser's dev tools, you see that the response for page 3 is an empty array, but the response for page 2 is correct. This is a common issue that can occur when using React Query, and it can be difficult to determine the root cause.

Debugging the Issue

The first step in debugging this issue is to take a look at the code that's making the API call. In our case, it's the getIssues function. This function is using the axios library to make the API request and pass the response to React Query.

export async function getIssues(
  page: number,
  projectId?: string | undefined,
  options?: { signal?: AbortSignal }
) {
  const { data } = await axios.get<Page<Issue>>(ENDPOINT, {
    params: projectId ? { page, projectId } : { page },
    signal: options?.signal,
  });

  if (projectId === undefined) {
    return data;
  } else {
    data.items = data.items.filter((item) => item.projectId === projectId);
  }
  return data;
}

As you can see from the code above, the function is using the projectId parameter to filter the results. If the projectId is not specified, the function returns the raw data with no filtering. However, if the projectId is specified, the function filters the data to only include objects with a matching projectId. There are several approaches that you can use to troubleshoot this issue:

1. Verify the API request: Ensure that the API endpoint URL and the request parameters are correct. You can use tools such as Postman to make API requests and check the response.

2. Inspect API response: Use the browser's DevTools to inspect the API response and check if it contains the expected data.

3. Debug the API call: You can add logging statements or breakpoints in your code to track the API request and response.

4. Check API status: Verify that the API is up and running and that you have the necessary permissions to access the data.

5. Try a different API endpoint: If the API request returns an unexpected result, try a different endpoint or API to get the data.

It's also important to keep in mind that the API response might be correct, and the issue could be with the way the data is processed or displayed in the frontend. In this case, you might need to debug the front-end code or check the data structures and types in your code.

Anyway, I chose to add logging statements to the code to track the API request and response. Here are some logging statements that I added to help debug my getIssues function:

1. Logging the URL and the parameters being passed to axios.get to make sure that the correct URL and parameters are being used.

console.log(`URL: ${ENDPOINT}`);
console.log(`Params: ${JSON.stringify(projectId ? { page, projectId } : { page })}`);

1. Logging the response object and the error object to see if the API call is returning the expected data or if there are any errors.

console.log(`Response: ${JSON.stringify(data)}`);
console.log(`Error: ${JSON.stringify(error)}`);

1. Logging the value of projectId to make sure it is the value I expected.

console.log(`projectId: ${projectId}`);

These statements will give me more information about what is happening in the function and hopefully help me to identify the issue.

export async function getIssues(
  page: number,
  projectId?: string | undefined,
  options?: { signal?: AbortSignal }
) {
  const { data } = await axios.get<Page<Issue>>(ENDPOINT, {
    params: projectId ? { page, projectId } : { page },
    signal: options?.signal,
  });
  console.log(`URL: ${ENDPOINT}`);
  console.log(`projectId: ${projectId}`);
  console.log(`Params: ${JSON.stringify(projectId ? { page, projectId } : { page })}`);
  console.log(`Response: ${JSON.stringify(data.items)}`);
  console.error(`Error: ${JSON.stringify(Error)}`);

  if (projectId === undefined) {
    console.log('items: ', data.items)
    return data;
  } else {
    data.items = data.items.filter((item) => item.projectId === projectId);
    console.log("filtered items: ", data.items)
  }
  return data;
}

By examining the console in the dev tools, I discovered that projectId for page 2 is undefined, whereas projectId for page 3 is blank or an empty string.

Solution

After examining the code, it's clear that the issue is related to the if (projectId === undefined) { return data; } statement. This statement only returns the data if the projectId is undefined, but what if it's an empty string? In this case, it would be handled by the else { data.items = data.items.filter((item) => item.projectId === projectId); } statement, which made the empty string go through the filtering step and setting the data.items response to an empty array for page 3.

To fix this issue, I needed to update the if statement to return the data if the projectId value is either undefined or an empty string.

if (projectId === undefined || projectId === '') { return data; }

With this change, the getIssues function will now return the data in both cases, even if the projectId is an empty string. In addition, I was able to render the data on the website and pass the end-2-end testing.

Conclusion

In conclusion, debugging an issue with an empty response from an API call can be a challenging task, especially when the issue is in the data retrieval function. However, by using the appropriate logging statements and carefully examining the logs, we were able to identify the root cause of the issue and resolve it by updating our code.

As a self-learner, this experience has taught me the importance of being able to effectively debug issues and the value of having a systematic approach when solving problems. I hope this post has been helpful to those who are also looking to improve their debugging skills and that it has inspired you to continue learning and growing as a developer.Happy coding!

If you found this post helpful, I would love to hear from you! Feel free to share your thoughts and feedback in the comments section below. Let's continue to learn and grow together as a community of self-learners!