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Asked: 2025-01-03T04:44:41+05:30

I’m encountering an issue with making a JavaScript fetch request to my Flask backend server. Despite my attempts, I’m getting a TypeError that says “failed to fetch.” I’m unsure what might be causing this problem. Could it be related to CORS, network issues, or something else? Any insights on how to troubleshoot and resolve this would be greatly appreciated.

I’m really stuck with an issue I’m having while trying to make a fetch request from my JavaScript code to my Flask backend. I’ve been debugging for hours and still can’t crack it. I keep getting this annoying TypeError that says “failed to fetch.” It’s driving me nuts!

So, here’s what I have: I’m using the Fetch API to send a request to my Flask server, which is running locally on port 5000. The code looks pretty standard; I’m just trying to grab some data from a specific endpoint. But every time I run it, I get this error. I’ve double-checked the URL and it’s correct, so that’s not the issue.

At first, I wondered if it could be a network issue, but everything else is working fine. My Flask app is running, and I can see it serving requests using Postman without any problems. I’ve also checked the console in my browser, and aside from the “failed to fetch” error, there are no other related messages. This is where I start to think maybe it’s a CORS issue? I’ve read that browsers can block requests if the server isn’t set up to allow them from different origins. I’ve already added the Flask-CORS package to my Flask app and set it to allow all origins during testing. Still, nothing seems to change.

I’m also considering if I might be misconfiguring the request headers or method. I’m making a GET request, so I thought it would work just fine. Could there be some small mistake I’m overlooking? I’m not doing anything fancy—just a simple data fetch. Is there maybe some additional configuration that I’m missing?

I’ve seen some threads online with similar issues, but they seem to be with deployments or complex setups. Since I’m just working locally, I’m starting to feel a bit lost. Any tips or insights on what I can try next would be super helpful! What steps should I take to troubleshoot this, and could there be other potential reasons for the “failed to fetch” error? Thanks for any help you can offer!

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    2 Answers

    1. It sounds like you’ve thoroughly investigated the common causes of a “failed to fetch” error when making requests from your JavaScript code to your Flask backend. Since you already verified that your Flask application is functional when tested with Postman, it’s likely that the issue resides in the client-side configuration or network policies enforced by the browser. First, ensure that your fetch request uses the correct protocol (HTTP or HTTPS). If you are accessing your Flask server via http://localhost:5000, ensure you are not inadvertently trying to access it via https, as browsers block such requests to a non-secure endpoint. Additionally, double-check the exact endpoint you are trying to access; even a slight deviation in the URL can lead to a failed fetch.

      Regarding CORS, since you’ve added the Flask-CORS package and allowed all origins, ensure that the CORS settings are correctly applied before any routes are defined in your Flask application. You might want to review your fetch request configuration for headers or other settings that may result in a misconfiguration. For debugging, you can also use try-catch blocks around your fetch request to capture more detailed error messages. If all else fails, try using the network tab in your browser’s developer tools to inspect the request and response. Look for any failed requests and their details; this could provide insight into whether it’s a CORS issue, an issue with the request itself, or something else entirely. Lastly, clear your browser cache and refresh to ensure you’re testing with the most recent code changes.

    2. Fetch Request Troubleshooting

      It sounds like you’ve been dealing with a really frustrating issue! The “failed to fetch” error can definitely be annoying, especially when everything looks good on the surface. Here are some things you can check and try to help solve your problem:

      1. Check the URL

      Even though you’ve already double-checked the URL, just make sure it includes the right protocol (http:// or https://), and make sure there’s no trailing slash if your Flask endpoint doesn’t expect one.

      2. CORS Issues

      Since you’re working locally, CORS issues are a common culprit. You mentioned you added Flask-CORS. Here’s a quick setup:

      from flask_cors import CORS
app = Flask(__name__)
CORS(app)

      Make sure this is happening right after you initialize your Flask app. If you want to allow specific origins, you might try something like CORS(app, resources={r"/your-endpoint": {"origins": "http://localhost:3000"}}) just to test.

      3. Run Flask on the Correct Port

      Check if your Flask app is indeed running on port 5000 and receiving your requests. Sometimes, it might be running on a different port if you accidentally specified it somewhere.

      4. Look at the Fetch Request

      Make sure your fetch request is appropriately structured. Here’s a simple outline:

      fetch('http://localhost:5000/your-endpoint')
    .then(response => {
        if (!response.ok) {
            throw new Error('Network response was not ok');
        }
        return response.json();
    })
    .then(data => console.log(data))
    .catch(error => console.error('There has been a problem with your fetch operation:', error));

      5. Check for Network Issues in Browser

      Open your browser’s dev tools (usually F12) and look for the ‘Network’ tab. Try making your request again and see if it shows up there. You might get more details on any errors that are occurring.

      6. Flask Logs

      If there are still issues, check the console output of your Flask application. It may log some useful information about what’s going wrong.

      7. Firewall or Antivirus Software

      Sometimes firewall or security software can interfere with local server requests, so you might want to check that too.

      8. Clear Browser Cache

      If you’ve been testing a lot, sometimes your browser cache can get in the way. Try clearing the cache or using an incognito window.

      By trying out these steps, you might just stumble upon the solution! It can be super tricky to debug these things, but keep at it. You’ve got this!