How to properly set axios default headers

Question

I'm using reactjs for my project but I have one issue, in config.js file where i set my global axios configurations, I'm setting default headers for axios requests but when i make axios request it does not send those headers in requests.

config.js

import axios from 'axios';

const instance = axios.create({
    baseURL: 'URL/api'
});

export const setAuthToken = (token) => {
    if (token) {
        // Apply to every request
        instance.defaults.headers.common['Authorization'] = 'Bearer ' + token;
    } else {
        // Delete auth header
        delete instance.defaults.headers.common['Authorization'];
    }
};

export default instance;

Login.js

import axios from '../../../config';
import { setAuthToken } from '../../../config';
axios
            .post('/auth/signin', {
                username: email,
                password: password
            })
            .then((res) => {
                setCurrentUser(res.data);
                setAuthToken(res.data.accessToken);
                setLoading(false);
            })
            .catch((err) => {
                console.log(err);
                setLoading(false);
                setError(true);
            });

Answer 1

You can use axios interceptors for this task.

1-) Inside the successfull login, put the retrieved token to the localStorage. Remove setAuthToken line.

 .then((res) => {
                setCurrentUser(res.data);
                localStorage.setItem("token", res.data.accessToken);
                setLoading(false);
            })

2-) Add this interceptor to your axios instance.

const instance = axios.create({
    baseURL: 'URL/api'
});

instance.interceptors.request.use(
  function(config) {
    const token = localStorage.getItem("token"); 
    if (token) {
      config.headers["Authorization"] = 'Bearer ' + token;
    }
    return config;
  },
  function(error) {
    return Promise.reject(error);
  }
);

Answer 2

I had to create the header object structure within the instance for global header overriding to work:

The code snippet below does not working (but it does not raise any error); global header is used when using the instance:

// Index.js
axios.defaults.headers.common['Authorization'] = 'AUTH_TOKEN';

// myAxios.js
const instance = axios.create({
  baseURL: 'https://jsonplaceholder.typicode.com'
});

instance.defaults.headers.common['Authorization'] = 'AUTH_TOKEN_FROM_INSTANCE';

This does work, instance header overrides the global default:

// Index.js
axios.defaults.headers.common['Authorization'] = 'AUTH_TOKEN';

// myAxios.js
const instance = axios.create({
  baseURL: 'https://jsonplaceholder.typicode.com',
  headers: {
    common: {
      Authorization: 'AUTH_TOKEN_FROM_INSTANCE'
    }
  }
});

It seems to me that this object structure should be created by default when using #create.

===========================================================================

Additionally, if you want to unset the header don't use delete. Here's a test:

it('should remove default headers when config indicates', function (done) {
  var instance = axios.create();
  instance.defaults.headers.common['Content-Type'] = 'application/json';

  instance.post('/foo/bar/', {
    firstName: 'foo',
    lastName: 'bar'
  }, {
    headers: {
      'Content-Type': null
    }
  });

  getAjaxRequest().then(function (request) {
    testHeaderValue(request.requestHeaders, 'Content-Type', null);
    done();
  });
});