xmlhttprequest upload 实现前端上传进度

element ui upload代码片段

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).forEach(key => {
      formData.append(key, option.data[key]);
    });
  }

  formData.append(option.filename, option.file, option.file.name);

  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));
    }

    option.onSuccess(getBody(xhr));
  };

  xhr.open('post', action, true);

  if (option.withCredentials && 'withCredentials' in xhr) {
    xhr.withCredentials = true;
  }

  const headers = option.headers || {};

  for (let item in headers) {
    if (headers.hasOwnProperty(item) && headers[item] !== null) {
      xhr.setRequestHeader(item, headers[item]);
    }
  }
  xhr.send(formData);
  return xhr;
}