module.js

// singleton export

const api = axios.create({
  bar: 'foo'
});

export default api;

// build export

const api = () => {
  return axios.create({
    bar: 'foo'
  });
}

export default api;

// build singleton export 

let _api;

const api = () => {
  return _api ? _api : _api = axios.create({
    bar: 'foo'
  });
}

export default api;