If you're building modern web applications, you've probably encountered the dreaded "Failed to Fetch" error at some point. This common JavaScript error happens when your web app can’t connect to a server or resource, leading to frustrating moments for both users and developers. But what exactly causes this issue, and how can you fix it?

In our detailed blog post, we break down the common causes behind this error and how you can troubleshoot it effectively. Here's a quick overview of the key points.

What Causes the "Failed to Fetch" Error?

The "Failed to Fetch" error can happen for a number of reasons. In most cases, it's not your code that's the problem, but rather something external—such as a network or server issue. Let’s take a look at the most common causes:

1. Network Problems

Often, the issue is on the user’s side, such as a poor or lost internet connection. When the network fails, your app won’t be able to reach the server, and you'll see this error. Other user-side problems like firewalls or proxy blocks can also prevent successful communication.

While developers can’t control user environments, it’s still important to build apps that handle these scenarios gracefully. You can learn more about managing network issues in our full article.

2. Server Issues

Server problems, like downtime or misconfigured paths, are another common cause of this error. For instance, if your app is trying to request data from an API and the server returns a 404 (Not Found) or 500 (Internal Server Error) response, you’ll run into the "Failed to Fetch" problem.

It’s essential to check your server’s availability and configuration when troubleshooting this issue. Read more on how to diagnose server problems in our blog post.

3. CORS Restrictions

Cross-Origin Resource Sharing (CORS) settings are a frequent culprit behind this error. If you’re making requests to a different domain, your server needs to allow it by setting the proper CORS headers. If the CORS headers are missing or incorrect, the browser will block the request—even if everything else is working.

CORS issues can be tricky to diagnose, but we’ve outlined some tips here to help you resolve them.

4. Browser Security Policies

Modern browsers enforce strict security policies to protect users. For example, most browsers now require that any sensitive requests happen over HTTPS. If you’re making requests from an insecure (HTTP) origin, the browser may block them for security reasons.

If you're seeing the "Failed to Fetch" error in this scenario, double-check that all your requests are going through secure channels. You can find additional troubleshooting steps in the original article.

How to Fix the "Failed to Fetch" Error

When troubleshooting the "Failed to Fetch" error, the first step is to isolate the root cause. Here's a quick checklist of what to investigate:

• Network conditions: Test the network to see if it's reliable and free from restrictions.
• Server availability: Ensure the server is running, and the API paths are correct.
• CORS headers: Make sure that the server is configured to allow cross-origin requests if needed.
• HTTPS enforcement: Verify that all requests are sent over secure (HTTPS) connections to avoid browser security blocks.

Conclusion

The "Failed to Fetch" error can be a pain to deal with, but with the right approach, it’s usually straightforward to resolve. Whether it’s a network issue, server misconfiguration, CORS setting, or browser security policy, understanding the underlying cause is key.

For more in-depth details, troubleshooting tips, and examples, check out our full blog post here.