text() method not available in Blob

Question

I am doing some Integration tests with jest & nock to test Axios interceptors chaining.
In one of them, I am expecting to receive a Blob instance
and according to this link, I should be able to use its text() method.
My question is: Why is this method not defined? (in my tests)

Here is the (simplified) code:

// interceptors.js
const useBlobTextProperty = async (response) => {
  const { data: myBlob } = response
  console.log(myBlob.toString())          // Prints "[object Blob]"
  response.rawText = await myBlob.text()  // TypeError: myBlob.text is not a function
  return response
}

// foo.test.js
import axios from 'axios'
import httpAdapter from 'axios/lib/adapters/http'
import nock from 'nock'

const testAxios = axios.create({
  responseEncoding: 'utf8',
  responseType: 'blob',
})
testAxios.interceptors.response.use(useBlobTextProperty, null)

const host = 'http://localhost'

axios.defaults.host = host
axios.defaults.adapter = httpAdapter

describe('SO test', () => {
  beforeEach(() => {
    nock(host)
      .defaultReplyHeaders({ 'Content-Type': 'application/json' })
      .persist()
      .get('/')
      .reply(200, { foo: 17 })
  })
  afterEach(() => {
    nock.cleanAll()
  })

  it('should get raw text', async () => {
    const returnValue = await testAxios.get('/') // FAIL: TypeError
    expect(returnValue.rawText).toEqual('{"foo":17}')
  }, 1000)
})

FYI, to workaround this issue, I am using another interceptor:

// interceptors.js
const addMissingTextPropertyToBlob = (response) => {
  const { data } = response
  if (data.toString() === '[object Blob]' && !data.text) {
    data.text = () =>
      new Promise((resolve, reject) => {
        const reader = new FileReader()
        reader.onload = () => { resolve(reader.result) }
        reader.onerror = (error) => { reject(error) }
        reader.readAsText(data)
      })
  }
  return response
}

// foo.test.js
// Response interceptors are executed from index 0 to N-1
testAxios.interceptors.response.use(addMissingTextPropertyToBlob, null)
testAxios.interceptors.response.use(useBlobTextProperty, null)
// Then, it works!

But I'd like to understand why I cannot rely on Blob.text() in my tests.

Answer 1

In my case, this approach worked for me:

yarn add blob-polyfill -D

and then import the following in your jest setupTests:

import 'blob-polyfill';