在chrome中使用EventSource时如何获取状态码？

var eventSource = new EventSource('your_event_source_url');

eventSource.onopen = function(event) {
  console.log('EventSource connection opened');
  console.log('Status Code: ' + event.target.readyState);
};

eventSource.onmessage = function(event) {
  console.log('Received message: ' + event.data);
};

eventSource.onerror = function(event) {
  console.log('Error occurred');
  console.log('Status Code: ' + event.target.readyState);
};

eventSource.onclose = function(event) {
  console.log('EventSource connection closed');
  console.log('Status Code: ' + event.target.readyState);
};