axios mocking via interceptors

mock-axios.js

import axios from 'axios'

let mockingEnabled = false

const mocks = {}

export function addMock(url, data) {
  mocks[url] = data
}

export function enableMocking(state) {
  mockingEnabled = state
}

const isUrlMocked = url => url in mocks

const getMockError = config => {
  const mockError = new Error()
  mockError.mockData = mocks[config.url]
  mockError.config = config
  return Promise.reject(mockError)
}

const isMockError = error => Boolean(error.mockData)

const getMockResponse = mockError => {
  const {mockData, config} = mockError
  // Handle mocked error (any non-2xx status code)
  if (mockData.status && String(mockData.status)[0] !== '2') {
    const err = new Error(mockData.message || 'mock error')
    err.code = mockData.status
    return Promise.reject(err)
  }
  // Handle mocked success
  return Promise.resolve(Object.assign({
    data: {},
    status: 200,
    statusText: 'OK',
    headers: {},
    config,
    isMock: true
  }, mockData))
}

// Add a request interceptor
axios.interceptors.request.use(config => {
  if (mockingEnabled && isUrlMocked(config.url)) {
    console.log('axios mocking ' + config.url)
    return getMockError(config)
  }
  return config
}, error => Promise.reject(error))

// Add a response interceptor
axios.interceptors.response.use(response => response, error => {
  if (isMockError(error)) {
    return getMockResponse(error)
  }
  return Promise.reject(error)
})

usage.js

import axios from 'axios'
import  {addMock, enableMocking} from './mock-axios'

addMock('https://dog.ceo/api/breeds/list/all', {data: {mock: 'dogs'}})
addMock('https://dog.ceo/404-page', {status: 404, message: 'whoops'})

enableMocking(true)

// mocked
let result = await axios.get('https://dog.ceo/api/breeds/list/all')
console.log(1, result)
try {
  result = await axios.get('https://dog.ceo/404-page')
} catch (err) {
  console.log(2, err)
}

// not mocked
result = await axios.get('https://dog.ceo/api/breeds/list/all?foo=1')
console.log(3, result)
try {
  result = await axios.get('https://dog.ceo/unhandled-404')
} catch (err) {
  console.log(4, err)
}