Axios middleware to use in all instances of axios

As per the documentation - You need to create a file i.e

// api-client.js

import axios from 'axios';

// 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
    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);

export default axios;

Then from your container or controller, import above file:

// Home.js
import apiClient from './api-client.js';

Interceptors are the Axios way of doing this. For me though, it was too limited, tangled in Axios' API, difficult to test, etc.


So I wrote the axios-middleware module, a simple middleware service that hooks itself in your axios instance (either global or a local one) and provides a simple, self-contained and easily testable middleware API.

Note: it shines in bigger apps where minimal coupling is really important.

Simple example

Here's a simple example from the documentation

import axios from 'axios';
import { Service } from 'axios-middleware';

const service = new Service(axios);

  onRequest(config) {
    return config;
  onSync(promise) {
    return promise;
  onResponse(response) {
    return response;

console.log('Ready to fetch.');

// Just use axios like you would normally.
  .then(({ data }) => console.log('Received:', data));

It should output:

Ready to fetch.
Received: {userId: 1, id: 1, title: ...

Testing a middleware

Say we have the following self-contained middleware class that we want to test.

export default class ApiErrorMiddleware {
  constructor(toast) {
    this.toast = toast;

  onResponseError(err = {}) {
    let errorKey = 'errors.default';
    const { response } = err;

    if (response && response.status) {
      errorKey = `errors.${response.status}`;
    } else if (err.message === 'Network Error') {
      errorKey = '';

    throw err;

Then it's really easy, we don't even need to mock Axios.

import ApiErrorMiddleware from '@/middlewares/ApiErrorMiddleware';

describe('ApiErrorMiddleware', () => {
  let toast;
  let middleware;

  // Jest needs a function when we're expecting an error to be thrown.
  function onResponseError(err) {
    return () => middleware.onResponseError(err);

  beforeEach(() => {
    toast = { error: jest.fn() };
    middleware = new ApiErrorMiddleware(toast);

  it('sends a code error message', () => {
    hasKey = true;
    expect(onResponseError({ response: { status: 404 } })).toThrow();