ajax - XMLHttpRequest.addEventListener 与 XMLHttpRequest.upload.addEventListener

Question

这段代码块有什么区别:

var xhr = new XMLHttpRequest();
xhr.upload.addEventListener("progress", uploadProgress, false);
xhr.addEventListener("load", uploadComplete, false);
xhr.addEventListener("error", uploadFailed, false);
xhr.addEventListener("abort", uploadCanceled, false);

xhr.open("POST", "upload_url");
xhr.send(some_form_data);

还有这个:

var xhr = new XMLHttpRequest();
xhr.upload.addEventListener("progress", uploadProgress, false);
xhr.upload.addEventListener("load", uploadComplete, false);
xhr.upload.addEventListener("error", uploadFailed, false);
xhr.upload.addEventListener("abort", uploadCanceled, false);

xhr.open("POST", "upload_url");
xhr.send(some_form_data);

我在博客和其他 SO 帖子中看到了这两种实现，但没有人解释为什么他们使用其中一个。目前我能找到的唯一区别是后者不适用于默认的 Android 浏览器，而前者似乎适用于几乎所有内容。

Answer 1

根据关于 XMLHttpRequest 的 w3c 规范。 http://www.w3.org/TR/XMLHttpRequest/#the-upload-attribute

As indicated earlier, each XMLHttpRequest object has an associated XMLHttpRequestUpload object.

Progress events exist for both download and upload transfers. The download events are fired on the XMLHttpRequest object itself, as shown in the above sample. The upload events are fired on the XMLHttpRequest.upload object