Error Code Reference

• ERR_CONN_REFUSED >

  Connection Refused

  The server actively refused the connection request. This typically means the service is not running, a firewall is blocking the connection, or the server is overloaded and cannot accept new connections.

  Common Causes:

  • The target service is not running on the server.
  • A firewall is blocking the port.
  • The server is at its connection limit.

  Resolution:

  • Ensure the service is running.
  • Check firewall rules.
  • Verify server resource availability.

  Example:

  fetch('http://localhost:8080/api/data')
    .then(response => response.json())
    .catch(error => console.error('Network error:', error));

• ERR_AUTH_INVALID_TOKEN >

  Invalid Authentication Token

  The provided authentication token is invalid, expired, or malformed. This prevents the user from accessing protected resources.

  Common Causes:

  • Expired token.
  • Incorrect token format.
  • Token has been revoked.
  • User logged out on another device.

  Resolution:

  • Prompt the user to re-authenticate.
  • Request a new token from the authentication server.

  Example:

  // Assuming 'token' is from localStorage or a cookie
  fetch('/api/user/profile', {
    headers: {
      'Authorization': `Bearer ${token}`
    }
  })
    .then(response => {
      if (!response.ok) throw new Error('Authentication failed');
      return response.json();
    })
    .catch(error => console.error('Auth error:', error));

• ERR_VALIDATION_FAILED >

  Validation Failed

  Input data failed to meet the required validation rules. This could be due to incorrect data types, missing required fields, or values outside acceptable ranges.

  Common Causes:

  • Required fields are empty.
  • Data format is incorrect (e.g., invalid email).
  • Numeric values are out of range.

  Resolution:

  • Provide clear feedback to the user on which fields failed validation and why.
  • Allow users to correct their input.

  Example:

  const email = 'invalid-email';
  if (!/\S+@\S+\.\S+/.test(email)) {
    console.error('ERR_VALIDATION_FAILED: Invalid email format.');
  }

• ERR_INTERNAL_SERVER_ERROR >

  Internal Server Error

  An unexpected condition occurred on the server. This is a generic error indicating that the server encountered a problem and could not fulfill the request.

  Common Causes:

  • Bugs in server-side code.
  • Database connection issues.
  • Resource exhaustion (memory, CPU).
  • Configuration errors.

  Resolution:

  • Check server logs for detailed error messages.
  • Debug server-side application logic.
  • Monitor server resources.

  Example:

  // Server-side (e.g., Node.js with Express)
  app.get('/data', (req, res) => {
    // Simulate an error
    throw new Error('Something went wrong on the server!');
    res.json({ message: 'Data fetched successfully' });
  });

• ERR_TIMEOUT >

  Request Timed Out

  The request took too long to complete and exceeded the allowed time limit. This can be due to slow network conditions or an unresponsive server.

  Common Causes:

  • Slow internet connection.
  • Server is overloaded or unresponsive.
  • Large data transfer.

  Resolution:

  • Check your network connectivity.
  • If the server is slow, consider optimizing server performance or increasing the timeout value (if applicable and safe).
  • Inform the user to try again later.

  Example:

  const controller = new AbortController();
  const timeoutId = setTimeout(() => controller.abort(), 5000); // 5 second timeout
  
  fetch('/api/long-operation', { signal: controller.signal })
    .then(response => response.json())
    .catch(error => {
      if (error.name === 'AbortError') {
        console.error('ERR_TIMEOUT: The request timed out.');
      } else {
        console.error('An error occurred:', error);
      }
    })
    .finally(() => clearTimeout(timeoutId));

• ERR_UNAUTHORIZED >

  Unauthorized Access

  The request requires authentication credentials that were not provided or were insufficient. The server understands the request but refuses to authorize it.

  Common Causes:

  • Missing API key or token.
  • Invalid or expired credentials.
  • User does not have the necessary permissions.

  Resolution:

  • Ensure the correct authentication credentials are sent with the request.
  • Verify user roles and permissions.
  • Prompt for login if necessary.

  Example:

  fetch('/api/admin/settings', {
    method: 'PUT',
    headers: {
      'Content-Type': 'application/json',
      // 'Authorization': 'Bearer YOUR_TOKEN_HERE' // Token is missing
    },
    body: JSON.stringify({ theme: 'dark' })
  })
  .then(response => {
    if (response.status === 401) throw new Error('ERR_UNAUTHORIZED: Please log in.');
    return response.json();
  })
  .catch(error => console.error('Access denied:', error));

• ERR_BAD_REQUEST >

  Bad Request

  The server cannot process the request due to something perceived to be a client error (e.g., malformed request syntax, invalid request message framing, or deceptive request routing).

  Common Causes:

  • Incorrectly formatted request body.
  • Missing required parameters.
  • Invalid request method.
  • Data type mismatch in request payload.

  Resolution:

  • Validate the request payload and parameters before sending.
  • Ensure the request adheres to the API specification.
  • Check for typos or syntax errors in the request.

  Example:

  fetch('/api/users', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({ name: 'Alice', age: 'twenty' }) // 'age' should be a number
  })
  .catch(error => console.error('Error submitting user data:', error));