The TypeError: Failed to fetch error is a common issue for developers using the Fetch API in JavaScript. It’s a generic error message that indicates a network request failed to complete. The cause can range from simple network connectivity problems to more complex server-side configurations like CORS.

This guide will walk you through the most common causes and how to resolve them.

What Causes “Failed to fetch”?

This error appears in the browser’s console when a fetch() request is initiated but cannot be completed. The browser doesn’t receive any response from the server. Key reasons include:

  1. Network Connectivity Issues: The most basic cause is a lack of internet connection or a firewall blocking the request.
  2. CORS (Cross-Origin Resource Sharing) Policy: This is the most frequent culprit. The server you are requesting data from does not permit your domain to access its resources.
  3. Incorrect URL or DNS Issues: The URL might be misspelled, or the domain name cannot be resolved by DNS.
  4. Blocked Request: The request might be blocked by the browser itself (e.g., mixed content blocking) or by a browser extension (like an ad blocker).
  5. Server Not Responding: The server at the specified URL might be down or unresponsive.

How to Fix “Failed to fetch”

Let’s break down the troubleshooting steps.

Step 1: Check Your Network Connection and the URL

Before diving into code, verify the basics:

  • Are you connected to the internet?
  • Is the server you’re trying to reach online? You can test this by pasting the API URL directly into your browser’s address bar.
  • Did you spell the URL correctly in your fetch() call? Check for typos in the domain, path, or protocol (http vs. https).

Step 2: Investigate CORS Issues

If the basics check out, the problem is likely CORS. A “Failed to fetch” error due to CORS means the server rejected the request before sending a response because the origin of the request (your web page) is not on its list of allowed origins.

How to check for CORS issues: Open your browser’s developer tools (F12), go to the Console tab. You will often see a more descriptive error message accompanying “Failed to fetch,” such as:

Access to fetch at '...' from origin '...' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.

Solution (if you control the server): You need to configure your server to include the Access-Control-Allow-Origin header in its responses. This header tells the browser which origins are permitted to access the server’s resources.

For a Node.js/Express server, you can use the cors middleware:

npm install cors

const express = require('express');
const cors = require('cors');
const app = express();

// Allow all origins
app.use(cors());

// Or, allow a specific origin
// app.use(cors({
//   origin: 'https://your-frontend-domain.com'
// }));

app.get('/api/data', (req, res) => {
  res.json({ message: 'Success!' });
});

app.listen(3001, () => console.log('Server is running'));

Solution (if you DON’T control the server): If you are using a third-party API, you cannot change its server-side CORS policy. The standard solution is to create a proxy server. Your application sends the request to your own server, which then makes the request to the third-party API and forwards the response back to your application. Since the server-to-server request is not subject to browser CORS policies, this approach works around the issue.

Step 3: Check for Mixed Content

Browsers block requests for HTTP resources from a page that was loaded over HTTPS. This is called “mixed content” blocking. Ensure that if your site is on https://, your API requests are also made to https:// endpoints.

Step 4: Disable Browser Extensions

Temporarily disable any ad blockers or privacy-related browser extensions to see if they are interfering with the network request.

Conclusion

The “Failed to fetch” error is a broad network-related error that requires systematic troubleshooting. Start with the simplest explanations—network connectivity and URL typos—before moving on to more complex issues like CORS policies. In most web development scenarios, a misconfigured CORS header on the server is the primary cause.

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