This instance has already started one or more requests. properties can only be modified before sending the first request

When you encounter the error message “This instance has already started one or more requests. Properties can only be modified before sending the first request,” it means that you are attempting to modify the properties of a request object after it has already been sent. Once a request is sent, its properties become read-only and cannot be modified.

To avoid this error, ensure that you make all necessary modifications to the request object before calling the send() method. Here’s an example to illustrate this:

      
         // Create a new XMLHttpRequest object
         var xhr = new XMLHttpRequest();
         
         // Set the request method and URL
         xhr.open('GET', 'https://api.example.com/data', true);
         
         // Set the request headers
         xhr.setRequestHeader('Content-Type', 'application/json');
         
         // Do any other necessary modifications to the request object
         xhr.timeout = 5000;  // Set a timeout value of 5 seconds
         xhr.withCredentials = true; // Enable cross-origin requests with credentials
         
         // Send the request
         xhr.send();
      
   

In the above example, all modifications to the request object (such as setting the timeout and withCredentials properties) are done before calling the send() method. This ensures that the properties are properly set and avoids the error mentioned in your query.