title: Safari 10 on Mac not uploading file in XHR
body: <p>I'm using XHR to upload an image to an external server which has CORS enabled.</p>
  
  <p>everything works fine in Chrome, Firefox and IE.</p>
  
  <p>But using Safari, server response with mime type error. saying the file type is 'application/octet-stream' while it should be 'image/*'.</p>
  
  <p>After I disabled mime type checking, safari can upload file but its all 0b empty file.</p>
  
  <p>anyone knows why?</p>
  
  <pre><code>    var xhr = new XMLHttpRequest();
      xhr.open('POST', 'http://up-z1.qiniu.com/', true);
      var formData;
      formData = new FormData();
      formData.append('key', file.name);
      formData.append('token', acessToken);
      formData.append('file', file);
      xhr.onreadystatechange = function (response) {
          if (xhr.readyState == 4 &amp;&amp; xhr.status == 200 &amp;&amp; xhr.responseText != "") {
              callback(true,null);
          } else if (xhr.status != 200 &amp;&amp; xhr.responseText) {
              callback(false,null);
          }
      };
      xhr.send(formData);
  </code></pre>