What is the shape of error object inside axios request interceptor error handler?

Technical note: As axios uses different libraries/mechanisms for Node and browser, this question touches only Node.js usage of axios@0.18.0.

I can set up the following interceptor for the axios library ( https://github.com/axios/axios#interceptors ):

// Add a request interceptor
axios.interceptors.request.use(function (config) {
    // Do something before request is sent
    return config;
  }, function (error) {
    // Do something with request error
    //
    // I am asking about this error handler and this error object
    //
    return Promise.reject(error);
  });

// Add a response interceptor
axios.interceptors.response.use(function (response) {
    // Do something with response data
    return response;
  }, function (error) {
    // Do something with response error
    return Promise.reject(error);
  });

When the callback described in error handler for request interceptor is triggered and and what is the shape of that error object?

P.S. I see that there is this code describing work with errors in axios:

axios.get('/user/12345')
  .catch(function (error) {
    if (error.response) {
      // The request was made and the server responded with a status code
      // that falls out of the range of 2xx
      console.log(error.response.data);
      console.log(error.response.status);
      console.log(error.response.headers);
    } else if (error.request) {
      //
      //
      //  !!!! This is a request error handler !!!
      //
      //
      // The request was made but no response was received
      // `error.request` is an instance of XMLHttpRequest in the browser and an instance of
      // http.ClientRequest in node.js
      console.log(error.request);
    } else {
      // Something happened in setting up the request that triggered an Error
      console.log('Error', error.message);
    }
    console.log(error.config);
  });

What will the error inside the request error handler represent in the latter code?

from What is the shape of error object inside axios request interceptor error handler?