Fixing Failed to Fetch errors in JavaScript

Stephen Cefali

Fixing “TypeError: Failed to Fetch” Errors in JavaScript

Introduction

The “TypeError: Failed to fetch” error can be a common and frustrating issue when working with web applications. This error is typically triggered by issues with the Fetch API, and there are several reasons why it might occur.

Common Causes of “Failed to Fetch” Errors

Incorrect or Incomplete URL

  • The URL passed to the fetch() method might be incorrect or incomplete.
  • Ensure the URL includes the correct protocol (https:// or http://), and the path is accurate.

CORS (Cross-Origin Resource Sharing) Issues

  • The server might not send back the correct CORS headers. If you’re not sure what CORS is, check out the MDN Docs.
  • Server configuration should include appropriate Access-Control-Allow-* headers.

Incorrect Fetch Configuration

  • Errors in the HTTP method or headers passed to the fetch() method.
  • Verify the correct configuration, including URL, HTTP method, and headers.

Browser Extensions

  • Sometimes, browser extensions can cause these errors. They might interfere with the API calls or modify the responses.

Steps to Debug

Check the URL

  • Ensure the URL used in the fetch() method is correct and complete.
  • Check for protocol, path accuracy, and HTTP method appropriateness.

Examine Browser Console

  • The browser console can provide more information about the failed API calls.
  • Look for errors related to CORS or other network issues.

Verify CORS Headers

  • Check if the server is sending the correct CORS headers.
  • Use the browser’s Network tab to inspect the headers of the failed requests.

Test with Different Configurations

  • Experiment with different fetch configurations to isolate the issue.
  • Try changing methods, headers, and URL formats.

Consider Proxy Usage

  • If modifying server headers isn’t feasible, use a proxy to bypass CORS issues.
  • Implement proxies using tools like express or cors-anywhere in Node.js.

Get Started With Sentry

Get actionable, code-level insights to resolve JavaScript performance bottlenecks and errors.

  1. Create a free Sentry account

  2. Create a JavaScript project and note your DSN

  3. Grab the Sentry JavaScript SDK

<script src="https://browser.sentry-cdn.com/7.102.0/bundle.min.js"></script>
  1. Configure your DSN
Sentry.init({ dsn: 'https://<key>@sentry.io/<project>' });

Check our documentation for the latest instructions.

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