Skip to main content

How to Resolve "TypeError: Failed to fetch" Error in JavaScript

The TypeError: Failed to fetch is a generic but very common error that occurs when a fetch() request fails at the network level. This is not an HTTP error like a 404 or 500; it's a more fundamental problem that prevented the browser from completing the request at all. The most common cause is a CORS (Cross-Origin Resource Sharing) policy violation, but it can also be caused by network connectivity issues.

This guide will explain what this error means, walk you through the most common causes, and provide a step-by-step process for debugging and fixing it.

The Core Problem: What Does "Failed to fetch" Mean?​

This error is a network error, not an HTTP error. It means the browser was unable to complete the request and receive a response. Think of it like a mail carrier being unable to find the recipient's address; the letter was never even delivered, so there's no response to read.

This is different from getting a 404 Not Found status code, which means the request was successfully delivered, but the server responded that the requested resource doesn't exist.

Cause 1 (Most Common): CORS Policy Issues​

CORS is a security mechanism enforced by browsers. If your frontend application (e.g., at https://example.com) tries to make a request to a backend API on a different domain (e.g., https://api.example.com), the browser will first send a "preflight" OPTIONS request to ask for permission.

The TypeError: Failed to fetch often occurs when:

  • The server does not respond to the preflight OPTIONS request.
  • The server responds but does not include the correct Access-Control-Allow-Origin header.

The browser sees this lack of permission and blocks the actual fetch request, which results in the generic "Failed to fetch" error in your JavaScript catch block, accompanied by a more detailed CORS error in the browser console.

Solution (server-side): This is a server-side issue. The backend API must be configured to send the correct CORS headers. For a Node.js/Express server, this is typically done with the cors middleware.

// Example of a correct server-side CORS configuration in Express
const cors = require('cors');
app.use(cors({
  origin: 'https://example.com' // Allow requests from your frontend's origin
}));

Cause 2: Network Connectivity and Server Issues​

Sometimes, the cause is much simpler and is not related to code.

  • No Internet Connection: The user's device is offline.
  • Server is Down: The API server you are trying to reach is offline or not running.
  • DNS Issues: The domain name cannot be resolved to an IP address.
  • Firewall or VPN: A firewall, proxy, or VPN is blocking the request.
  • Incorrect URL: The URL is malformed or has a typo in the domain name.

Solution: check your network connection, verify that the API server is running and accessible, and double-check that the URL in your fetch() call is spelled correctly.

Cause 3: Mixed Content and Other Security Blocks​

Browsers enforce strict security rules. One of these is blocking "mixed content."

  • Mixed Content: If your website is loaded over HTTPS, the browser will block any fetch requests made to an HTTP endpoint.

Solution: ensure that the API endpoint you are calling uses the same protocol (https-) as your main application.

How to Debug the Error (The Most Important Step)​

The TypeError: Failed to fetch message in your catch block is generic. The real error is almost always printed in your browser's Developer Console.

Step 1: Look at the Console Tab​

Open your browser's Developer Tools (F12) and go to the Console tab. You will almost always see a second, more specific error message that explains the true cause.

Example of a CORS error in the console:

Access to fetch at 'https://api.example.com/data' from origin 'http://localhost:3000' has been blocked by CORS policy: Response to preflight request doesn't pass access control check...

This message is your real clue. It tells you the problem is CORS.

Step 2: Look at the Network Tab​

Go to the Network tab to see the failed request in detail.

  • Filter the requests to find the one that failed. It will often be marked in red or have a status of (failed).
  • If the cause is CORS, you will likely see a failed OPTIONS request (the preflight). Click on it to inspect its headers and response. This can help you and the backend developer see exactly what is missing or incorrect.

Conclusion​

The TypeError: Failed to fetch is a generic network error, but you can quickly diagnose it by looking for more specific error messages in your browser's developer console.

To solve it, follow this diagnostic checklist:

  1. Check the Console: Look for a more detailed error message. Is it a CORS error? Is it a mixed content warning?
  2. Check the Network Tab: Inspect the failed request. Did the preflight (OPTIONS) request fail? Is the server responding at all?
  3. If it's a CORS issue, the solution is on the server. The backend must be configured to send the correct Access-Control-Allow-Origin headers.
  4. If it's not a CORS issue, check for network problems, server downtime, or typos in your URL.

Table of Contents