Скачать или смотреть Troubleshooting CORS Issues When Connecting to Your GraphQL API in Node.js

Discover solutions to fix `CORS` errors when connecting your front-end applications to a GraphQL API built with Node.js and Express.
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Troubleshooting CORS Issues When Connecting to Your GraphQL API in Node.js

Sending requests from your front-end to your back-end API can sometimes lead to frustrating issues, particularly related to Cross-Origin Resource Sharing (CORS). If you've encountered a situation where your front-end application cannot connect to your GraphQL API and you've received an error message stating "blocked by CORS policy," this guide will help you diagnose and rectify the problem.

Understanding the Problem

CORS is a security feature implemented by web browsers that restricts web pages from making requests to a different domain than the one that served the web page. This is how browsers prevent malicious sites from reading sensitive data from other sites.

In your case, you noted that one of your front-ends works flawlessly while the other throws a CORS error. This inconsistency can be confusing, but there are several key areas you can check to resolve the issue.

Solution: Adjusting Your CORS Configuration

1. Check Your CORS Setup

Based on the backend code you provided, it looks like you’re using the cors middleware in your Node.js application. Here’s how you've initially set it up:

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However, if your second front-end is running on a different port (for example, localhost:4000), the CORS configuration will not allow requests from this origin.

Update Your CORS Configuration

To support multiple front-end applications, modify your CORS configuration to allow requests from both front-ends:

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2. Use a Dynamic Origin

If you are deploying your application and need flexibility, you can allow requests from any origin by doing the following (not recommended for production due to security risks):

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3. Simplifying CORS Configuration

If the previous configurations don’t work, you can consider simplifying your CORS implementation by using app.use(cors()), as you tried earlier. This will allow requests from any origin, which can be useful during development.

4. Check Your Client-Side Code

Ensure your API URLs in both front-end applications are correct. Here’s an example based on your provided Apollo Client configuration:

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Make sure that the URL variable points to your deployed GraphQL API and that it matches the server's CORS settings.

5. Verify with ngrok

If you're using a service like ngrok to expose your local servers to the internet, double-check that the URLs it generates match what your client-side applications are using. Any mismatch can lead to CORS issues.

6. Token Management in Apollo Client

If your API requires authentication through tokens, ensure that they are being correctly set in the headers:

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Ensure your logic here is correct, and that the token is being retrieved and applied correctly.

Conclusion

CORS issues can be quite challenging to troubleshoot, particularly when dealing with multiple front-end applications and environments. By following the steps outlined above, you should be able to resolve CORS-related errors and ensure your applications can successfully communicate with your GraphQL API. If you continue to face problems, consider checking your browser's console for further clues or debugging server-side logs to identify any overlooked problems.

Happy coding!