How do I fix the "TypeError: Failed to fetch" error in JavaScript?

The "TypeError: Failed to fetch" error in JavaScript typically occurs when there is an issue with a fetch API call. This error indicates that the browser was unable to make the request due to network issues or security concerns, such as problems with CORS (Cross-Origin Resource Sharing), an invalid URL, or an offline network.

Here’s how to troubleshoot and fix it:

1. Check the URL

• Ensure the URL is correct and reachable. If the URL is wrong or mistyped, the fetch request will fail.
• Example:

fetch('https://api.example.com/data')
  .then(response => response.json())
  .then(data => console.log(data))
  .catch(error => console.error('Error:', error));

2. CORS Issue

• CORS restricts web pages from making requests to different domains unless the server allows it. If the server doesn’t send the proper headers, your request will be blocked by the browser.
• Example of a CORS error:

fetch('https://example.com/api/data', {
  method: 'GET',
  headers: {
    'Content-Type': 'application/json'
  }
})
.then(response => response.json())
.then(data => console.log(data))
.catch(error => console.error('Error:', error)); // TypeError: Failed to fetch

Solution: To fix CORS issues, you’ll need to either:

• Configure the server to send appropriate CORS headers.
• Use a proxy server to forward requests.

3. Network or Connectivity Issues

• If the client is offline or there is a network issue, the fetch will fail.
• Example:

fetch('https://example.com/api/data')
  .then(response => response.json())
  .then(data => console.log(data))
  .catch(error => {
    if (error.name === 'TypeError') {
      console.error('Network issue or offline:', error);
    }
  });

4. HTTPS Requirement

• If the request is made over HTTP instead of HTTPS, some browsers may block it for security reasons.
• Ensure that the API uses HTTPS:

fetch('https://secure-api.com/data')
  .then(response => response.json())
  .then(data => console.log(data))
  .catch(error => console.error('Error:', error));

5. Check for Missing Headers

• If the server expects specific headers, and they are missing, it might reject the request.
• Example:

fetch('https://example.com/api/data', {
  headers: {
    'Authorization': 'Bearer token123', // Add any required headers
  }
})
.then(response => response.json())
.then(data => console.log(data))
.catch(error => console.error('Error:', error));

6. Wrong HTTP Method

• Ensure you are using the correct HTTP method (GET, POST, etc.) and payload format if applicable.
• Example:

fetch('https://example.com/api/data', {
  method: 'POST', // Ensure the correct method is used
  body: JSON.stringify({ key: 'value' }), // Payload if needed
  headers: {
    'Content-Type': 'application/json'
  }
})
.then(response => response.json())
.then(data => console.log(data))
.catch(error => console.error('Error:', error));

Conclusion

• Always check the network response using browser developer tools for more details.
• Common issues like CORS or network connectivity are usually the culprit.