Fixing undefined Issues with Fetch API in Node.js

Learn how to resolve issues with undefined data when using the Fetch API in Node.js. Follow our step-by-step guide for effective solutions!
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This video is based on the question https://stackoverflow.com/q/67642278/ asked by the user 'CS student' ( https://stackoverflow.com/u/13081668/ ) and on the answer https://stackoverflow.com/a/67642390/ provided by the user 'epascarello' ( https://stackoverflow.com/u/14104/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Fixing undefined Issues with Fetch API in Node.js

When working with Node.js and attempting to fetch data from an API, it can be incredibly frustrating to encounter undefined responses. This commonly occurs when the data is indeed present but not properly formatted or manipulated before being sent to the browser.

If you are facing this issue, fret not! In this guide, we’ll dive into the problem, examine the code that’s causing the issue, and provide a clear solution to ensure that your data is displayed correctly.

The Problem: Getting undefined Instead of Your Data

You may have set up a route to fetch products from your database, but when you inspect the network responses in your browser, you see the expected data under Network, yet your app displays undefined.

This situation usually arises due to how you are handling arrays and data structures within your Node.js application. Let's take a closer look at the relevant code segment:

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

In this code, you are executing a query to retrieve products and pushing the result (rows) directly into array. The issue, however, lies in how you're pushing this data.

What’s Going Wrong?

The response from the database is an array of objects. By simply pushing rows to array, you are creating a 2D array structure, which leads to confusion when trying to display this data. The final output becomes nested, resulting in undefined when accessing it improperly.

The Solution: Use Spread Syntax to Flatten the Array

To resolve this issue, you should push the items from rows into your array as individual items instead of pushing the entire rows array at once. A clean and effective way to achieve this is by using the spread syntax (...).

Updated Code Implementation

Here's how you can modify the relevant part of your code:

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

Explanation of the Changes

Spread Syntax: The line array.push(...rows); will unpack (or spread) the elements of the rows array and push them individually into your array. This flattens the structure, converting a 2D array into a simple 1D array.

Response Handling: Using res.send(rows); continues to send the original array back to the client, while now array will also contain a proper structure for accessing that data.

Conclusion

By making a small adjustment in how you handle the fetched data in your Node.js application, you can ensure that the data displays correctly in the browser rather than appearing as undefined. Always keep in mind how your data structures are organized when dealing with arrays to avoid similar issues in the future.

If you encounter further issues or have questions, feel free to leave a comment. Happy coding!