前后台分离，全局请求加头部

_axios.interceptors.request.use(
  function(config) {
  var accessToken = localStorage.getItem('accessToken');
  if (accessToken && accessToken !== '') {
      config.headers.common['Authorization'] = accessToken;
  }
    return config;
  },
  function(error) {
    // Do something with request error
    return Promise.reject(error);
  }
);
// 响应拦截器获取 headers，设置(刷新) Token
// Add a response interceptor
_axios.interceptors.response.use(
  function(response) {
    // Do something with response data
        var accessToken = response.headers['authorization'];
        if (accessToken && accessToken !== '') {
            localStorage.setItem('accessToken',accessToken);
        }
        return response;
  },
  function(error) {
    // Do something with response error
    return Promise.reject(error);
  }
);