Home > Software > How to Fix JavaScript TypeError: Failed to Fetch Because of CORS

How to Fix JavaScript TypeError: Failed to Fetch Because of CORS

Anastasios Antoniadis

Share on X (Twitter) Share on Facebook Share on Pinterest Share on LinkedInIn modern web development, making network requests to retrieve or send data to external servers is commonplace. However, developers often encounter the TypeError: Failed to fetch error due to Cross-Origin Resource Sharing (CORS) restrictions. This article aims to demystify CORS, explain why this …

Javascript

In modern web development, making network requests to retrieve or send data to external servers is commonplace. However, developers often encounter the TypeError: Failed to fetch error due to Cross-Origin Resource Sharing (CORS) restrictions. This article aims to demystify CORS, explain why this error occurs, and provide practical solutions to resolve it, ensuring your JavaScript applications can successfully interact with external resources.

Understanding CORS

Cross-Origin Resource Sharing (CORS) is a security feature implemented in browsers to prevent malicious websites from accessing resources and data hosted on other websites without permission. According to the same-origin policy, a web application running at one origin (scheme, hostname, and port) can only request resources from the same origin. CORS is a mechanism that allows restricted resources on a web server to be requested from another domain outside the domain from which the first resource was served, but only if the server opts in using the proper headers.

Why the CORS Error Occurs

The TypeError: Failed to fetch error related to CORS usually happens when your JavaScript code makes a network request to a server that does not include the appropriate CORS headers in its response. This absence tells the browser that the server is not willing to share its resources with the origin your JavaScript code is running from, leading the browser to block the request and throw an error.

Resolving the CORS Issue

1. Enable CORS on the Server

The most straightforward solution is to configure the server to include CORS headers in its responses for the resources your application needs to access. Specifically, the server needs to set the Access-Control-Allow-Origin header to allow requests from your origin.

For example, to allow all origins (not recommended for production environments due to security concerns):

Access-Control-Allow-Origin: *

Or, to allow a specific origin:

Access-Control-Allow-Origin: https://www.example.com

Server configuration varies depending on the technology and platform used (Node.js, Apache, Nginx, etc.), so refer to your server’s documentation for instructions on enabling CORS.

2. Use a Proxy Server

If you don’t have control over the server’s configuration, another approach is to use a proxy server that adds the necessary CORS headers to the response before forwarding it to your application.

You can set up your own proxy server or use existing solutions. Many developers temporarily use public proxies like https://cors-anywhere.herokuapp.com/ for development purposes, but keep in mind the security and performance implications of relying on a third-party service.

3. Utilize CORS Anywhere

For development and testing, you can use “CORS Anywhere,” a Node.js proxy that adds CORS headers to a request. Running your instance of CORS Anywhere is straightforward and can be done by cloning its repository and deploying it to your development environment. This should not be used in production.

4. Leverage JSONP (with Caution)

JSONP (JSON with Padding) is an older technique for overcoming CORS limitations by using a <script> tag to load a resource from a different origin. While JSONP can bypass CORS, it’s limited to GET requests and poses significant security risks, as it can introduce cross-site scripting (XSS) vulnerabilities.

5. Adjust the Fetch Request Mode

When making fetch requests, setting the mode to no-cors in the request options object can suppress CORS errors. However, this approach also limits the type of responses you can read, making it suitable only for specific use cases.

fetch(url, {
  mode: 'no-cors'
  // other options...
});

Conclusion

Dealing with CORS errors requires an understanding of both the security implications and the technical solutions available. While enabling CORS on the server is the most straightforward and secure approach, alternatives like using a proxy server or CORS Anywhere can be viable for development or when you don’t control the server settings. Always prioritize security and privacy when implementing CORS solutions, ensuring that your applications remain robust and secure.

Anastasios Antoniadis
Follow me
0 0 votes
Article Rating
Subscribe
Notify of
guest
0 Comments
Inline Feedbacks
View all comments
0
Would love your thoughts, please comment.x
()
x