code: function post(url, data, successCallback, errorCallback) {
      const request = new XMLHttpRequest();
  
      request.open('POST', url, true);
      request.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded; charset=UTF-8');
  
      request.onreadystatechange = () => {
          if (request.readyState === 4) {
              /* Only 2xx codes are successful for the POST request. */
              if ((request.status >= 200) && (request.status < 300)) {
                  successCallback(request.responseText);
              } else {
                  console.error(`POST (${url}): error ${request.status} ${request.statusText}`);
                  errorCallback(request.status, request.statusText);
              }
          }
      };
  
      request.send(data);
  }
docs: Post ---- Makes a POST request and executes a success or error callback when the request state changes