根据响应的不同的 MIME 类型，传递给 success 回调函数的返回数据也有所不同，这些数据可以是 XML 根元素、文本字符串、Javascr ipt 文件或者 JSON 对象。也可向 success 回调函数传递响应的文本状态。(According to the different MIME types of response, the return data passed to the success callback function is also different. These data can be XML root elements, text strings, Javascr ipt files, or JSON objects. You can also pass the text state of the response to the success callback function.)