How would you localize bugs in case of no data…

Study application, server, and database logs.
Check network requests using developer tools (e.g., Chrome DevTools, Fiddler) for errors (status codes, missing requests).
Debug client and server code by setting breakpoints in the click handler and the method responsible for sending data.
Verify the API or endpoint configuration to which data is sent.
Ensure the request body (payload) is correctly formed and contains the right data.
Check access rights and authentication for performing the action.
Isolate the problem by testing data sending with third-party tools (e.g., Postman) or writing a minimal test script.
Review API documentation and data format requirements.
Check firewall or proxy server settings if used.
Look for parallel processes or locks that might interfere with data sending.

Example of debugging in JavaScript (client-side):

// Example of debugging a click event handler
document.getElementById('myButton').addEventListener('click', function() {
  console.log('Button clicked.'); // Check if handler triggers
  const dataToSend = { key: 'value' }; // Data to send
  console.log('Data to send:', dataToSend); // Check the data being formed

  fetch('/api/sendData', {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
    },
    body: JSON.stringify(dataToSend),
  })
  .then(response => {
    console.log('Fetch response received.'); // Check if response is received
    if (!response.ok) {
      throw new Error(`HTTP error! status: ${response.status}`); // Handle HTTP errors
    }
    return response.json();
  })
  .then(data => {
    console.log('Response data:', data); // Check response data
  })
  .catch(error => {
    console.error('Error sending data:', error); // Log sending errors
  });
});

Example of network request check in Chrome DevTools:

Open DevTools (F12).
Go to the "Network" tab.
Click the button in the application.
Find the request that should have been sent.
Check the status code (should be 2xx for success).
Examine the "Headers", "Payload", "Preview", "Response" tabs for request and response details.

Example of server log check (Python/Flask):

# Example of logging in request handler
@app.route('/api/sendData', methods=['POST'])
def send_data():
    try:
        data = request.get_json()
        app.logger.info(f"Received data: {data}") # Log received data
        # ... process data ...
        return jsonify({"status": "success"}), 200
    except Exception as e:
        app.logger.error(f"Error processing data: {e}") # Log errors
        return jsonify({"status": "error", "message": str(e)}), 500

A comparative analysis of data sent from the client and received on the server can also help identify discrepancies.

How would you localize bugs in case of no data transfer when pressing a button?