text: // https://github.com/ElemeFE/element/blob/dev/packages/upload/src/ajax.js
  
  function getError (action, option, xhr) {
      const msg = `fail to post ${action} ${xhr.status}'`;
      const err = new Error(msg);
      err.status = xhr.status;
      err.method = 'post';
      err.url = action;
      return err;
  }
  
  function getBody (xhr) {
      const text = xhr.responseText || xhr.response;
      if (!text) {
          return text;
      }
  
      try {
          return JSON.parse(text);
      } catch (e) {
          return text;
      }
  }
  
  export default function upload (option) {
      if (typeof XMLHttpRequest === 'undefined') {
          return;
      }
  
      const xhr = new XMLHttpRequest();
      const action = option.action;
  
      if (xhr.upload) {
          xhr.upload.onprogress = function progress (e) {
              if (e.total > 0) {
                  e.percent = e.loaded / e.total * 100;
              }
              option.onProgress(e);
          };
      }
  
      const formData = new FormData();
  
      if (option.data) {
          Object.keys(option.data).map(key => {
              formData.append(key, option.data[key]);
          });
      }
  
      formData.append(option.filename, option.file);
  
      xhr.onerror = function error (e) {
          option.onError(e);
      };
  
      xhr.onload = function onload () {
          if (xhr.status < 200 || xhr.status >= 300) {
              return option.onError(getError(action, option, xhr), getBody(xhr));
          }
  
          option.onSuccess(getBody(xhr));
      };
  
      xhr.open('post', action, true);
  
      if (option.withCredentials && 'withCredentials' in xhr) {
          xhr.withCredentials = true;
      }
  
      const headers = option.headers || {};
  
      // if (headers['X-Requested-With'] !== null) {
      //   xhr.setRequestHeader('X-Requested-With', 'XMLHttpRequest');
      // }
  
      for (let item in headers) {
          if (headers.hasOwnProperty(item) && headers[item] !== null) {
              xhr.setRequestHeader(item, headers[item]);
          }
      }
      xhr.send(formData);
  }
  