code: function statusValid (xhr) {
  	try {
  		var status = xhr.status
  		return (status !== null && status !== 0)
  	} catch (e) {
  		return false
  	}
  }
docs: Checks if xhr.status is readable and non-zero, indicating no error.
  Even though the spec says it should be available in readyState 3,
  accessing it throws an exception in IE8