TypeError：undefined不是对象（评估“ this.text”）

Question

When running App PutainDeBiere ( http://putaindecode.io/fr/articles/js/react/native/introduction/ ) on Android emulator, I get this error :

TypeError: undefined is not an object (evaluating 'this.text')

in ..\\node_modules\\whatwg-fetch\\fetch.js:296:18 executing this :

this.json = function() {
  return this.text().then(JSON.parse)
}

I use this example on an Android emulator :

index.js --->

import React, { Component } from "react";
import { AppRegistry, 
    StyleSheet, 
    ActivityIndicator, // import des composants
    TouchableOpacity,
    Text, 
    View 
    } from "react-native";

import { getRandomBrewdog } from './app'

class App extends Component {

constructor(props) {
super(props)

// la state de notre composant est utilisé pour
// stocker quelques infos renvoyées par l'API
this.state = {
  name: '', // nom de la bière
  description: '', // sa description
  isLoading: false // la requête API est-elle en cours ?
}
}

// nous externalisons cette fonction afin de
// pouvoir l'appeler lorsqu'on le souhaite
_getRandomBrewdogWithFeedback = () => {
this.setState({ isLoading: true })

getRandomBrewdog()
  .then(json => this.setState({
    name: json.name,
    description: json.description,
    isLoading: false // la requête est terminée
  }))
  .catch(error => console.error(error))
}

componentWillMount() {
this._getRandomBrewdogWithFeedback()
}


render() {
const content = this.state.isLoading
  ? <ActivityIndicator /> // si requête en cours, on affiche un spinner
  : <View style={styles.infosContainer}>
      <Text style={styles.name}>
        {this.state.name} // sinon on affiche le nom de la bière
      </Text>

      <Text style={styles.description}>
        {this.state.description} // sa description
      </Text>

      <TouchableOpacity // on ajoute un "bouton" qui requête une autre bière  aléatoire
        onPress={this._getRandomBrewdogWithFeedback}
        style={styles.button}
      >
        <Text>Grab a new beer!</Text>
      </TouchableOpacity>
    </View>

return (
  <View style={styles.container}>
    {content}
  </View>
)
}


}

const styles = StyleSheet.create({
container: {
flex: 1,
justifyContent: 'center',
alignItems: 'center',
backgroundColor: '#F5FCFF',
},
// ajout de styles divers
infosContainer: {
margin: 30,
},
name: {
fontSize: 18,
fontWeight: '700',
marginBottom: 10,
},
description: {
marginBottom: 10,
},
button: {
borderWidth: 1,
borderColor: '#000',
borderRadius: 3,
padding: 5,
justifyContent: 'center',
alignItems: 'center',
}
})

---> app.js

import base64 from "base-64"; // importez la dépendance tout juste installée

const rootEndpoint = "https://api.punkapi.com/v2";
// pour simplifier la compréhension de ce tuto, nous renseignons la clé   API "en dur"
// ne faites jamais cela au sein de vos projets (voir   http://12factor.net/fr/config)
const punkApiKey = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";
const password = ""; // la punk API n'utilise aucun mot de passe
const authBase64 = base64.encode(`${punkApiKey}:${password}`);

const headers = {
"Content-Type": "application/json",
Accept: "application/json",
Authorization: `Basic ${authBase64}` // HTTP basic auth
};

// retourne une recette de bière au hasard
export const getRandomBrewdog = () =>
fetch(`${rootEndpoint}/beers/random`, { headers }).then(
({ status, json }) => {
  if (status !== 200)
    throw new Error(`API answered with status code ${status}`); // gestion du status code HTTP
  else return json(); // on parse la réponse en JSON
}
);

--> fetch.js

(function(self) {
'use strict';

if (self.fetch) {
return
}

var support = {
searchParams: 'URLSearchParams' in self,
iterable: 'Symbol' in self && 'iterator' in Symbol,
blob: 'FileReader' in self && 'Blob' in self && (function() {
  try {
    new Blob()
    return true
  } catch(e) {
    return false
  }
})(),
formData: 'FormData' in self,
arrayBuffer: 'ArrayBuffer' in self
}

if (support.arrayBuffer) {
var viewClasses = [
  '[object Int8Array]',
  '[object Uint8Array]',
  '[object Uint8ClampedArray]',
  '[object Int16Array]',
  '[object Uint16Array]',
  '[object Int32Array]',
  '[object Uint32Array]',
  '[object Float32Array]',
  '[object Float64Array]'
]

var isDataView = function(obj) {
  return obj && DataView.prototype.isPrototypeOf(obj)
}

var isArrayBufferView = ArrayBuffer.isView || function(obj) {
  return obj && viewClasses.indexOf(Object.prototype.toString.call(obj)) > -1
}
}

function normalizeName(name) {
if (typeof name !== 'string') {
  name = String(name)
}
if (/[^a-z0-9\-#$%&'*+.\^_`|~]/i.test(name)) {
  throw new TypeError('Invalid character in header field name')
}
return name.toLowerCase()
}

function normalizeValue(value) {
if (typeof value !== 'string') {
  value = String(value)
}
return value
}

// Build a destructive iterator for the value list
function iteratorFor(items) {
var iterator = {
  next: function() {
    var value = items.shift()
    return {done: value === undefined, value: value}
  }
}

if (support.iterable) {
  iterator[Symbol.iterator] = function() {
    return iterator
  }
}

return iterator
}

function Headers(headers) {
this.map = {}

if (headers instanceof Headers) {
  headers.forEach(function(value, name) {
    this.append(name, value)
  }, this)

} else if (headers) {
  Object.getOwnPropertyNames(headers).forEach(function(name) {
    this.append(name, headers[name])
  }, this)
}
}

Headers.prototype.append = function(name, value) {
name = normalizeName(name)
value = normalizeValue(value)
var list = this.map[name]
if (!list) {
  list = []
  this.map[name] = list
}
list.push(value)
}

Headers.prototype['delete'] = function(name) {
delete this.map[normalizeName(name)]
}

Headers.prototype.get = function(name) {
var values = this.map[normalizeName(name)]
return values ? values[0] : null
}

Headers.prototype.getAll = function(name) {
return this.map[normalizeName(name)] || []
}

Headers.prototype.has = function(name) {
return this.map.hasOwnProperty(normalizeName(name))
}

Headers.prototype.set = function(name, value) {
this.map[normalizeName(name)] = [normalizeValue(value)]
}

Headers.prototype.forEach = function(callback, thisArg) {
Object.getOwnPropertyNames(this.map).forEach(function(name) {
  this.map[name].forEach(function(value) {
    callback.call(thisArg, value, name, this)
  }, this)
}, this)
}

Headers.prototype.keys = function() {
var items = []
this.forEach(function(value, name) { items.push(name) })
return iteratorFor(items)
}

Headers.prototype.values = function() {
var items = []
this.forEach(function(value) { items.push(value) })
return iteratorFor(items)
}

Headers.prototype.entries = function() {
var items = []
this.forEach(function(value, name) { items.push([name, value]) })
return iteratorFor(items)
}

if (support.iterable) {
Headers.prototype[Symbol.iterator] = Headers.prototype.entries
}

function consumed(body) {
if (body.bodyUsed) {
  return Promise.reject(new TypeError('Already read'))
}
body.bodyUsed = true
}

function fileReaderReady(reader) {
return new Promise(function(resolve, reject) {
  reader.onload = function() {
    resolve(reader.result)
  }
  reader.onerror = function() {
    reject(reader.error)
  }
})
}

function readBlobAsArrayBuffer(blob) {
var reader = new FileReader()
var promise = fileReaderReady(reader)
reader.readAsArrayBuffer(blob)
return promise
}

function readBlobAsText(blob) {
var reader = new FileReader()
var promise = fileReaderReady(reader)
reader.readAsText(blob)
return promise
}

function readArrayBufferAsText(buf) {
var view = new Uint8Array(buf)
var chars = new Array(view.length)

for (var i = 0; i < view.length; i++) {
  chars[i] = String.fromCharCode(view[i])
}
return chars.join('')
}

function bufferClone(buf) {
if (buf.slice) {
  return buf.slice(0)
} else {
  var view = new Uint8Array(buf.byteLength)
  view.set(new Uint8Array(buf))
  return view.buffer
}
}

  function Body() {
  this.bodyUsed = false

  this._initBody = function(body) {
  this._bodyInit = body
  if (!body) {
    this._bodyText = ''
  } else if (typeof body === 'string') {
    this._bodyText = body
  } else if (support.blob && Blob.prototype.isPrototypeOf(body)) {
    this._bodyBlob = body
  } else if (support.formData && FormData.prototype.isPrototypeOf(body)) {
    this._bodyFormData = body
  } else if (support.searchParams && URLSearchParams.prototype.isPrototypeOf(body)) {
    this._bodyText = body.toString()
  } else if (support.arrayBuffer && support.blob && isDataView(body)) {
    this._bodyArrayBuffer = bufferClone(body.buffer)
    // IE 10-11 can't handle a DataView body.
    this._bodyInit = new Blob([this._bodyArrayBuffer])
  } else if (support.arrayBuffer && (ArrayBuffer.prototype.isPrototypeOf  (body) || isArrayBufferView(body))) {
    this._bodyArrayBuffer = bufferClone(body)
  } else {
    throw new Error('unsupported BodyInit type')
  }

  if (!this.headers.get('content-type')) {
    if (typeof body === 'string') {
      this.headers.set('content-type', 'text/plain;charset=UTF-8')
    } else if (this._bodyBlob && this._bodyBlob.type) {
      this.headers.set('content-type', this._bodyBlob.type)
    } else if (support.searchParams &&   URLSearchParams.prototype.isPrototypeOf(body)) {
      this.headers.set('content-type', 'application/x-www-form-  urlencoded;charset=UTF-8')
    }
  }
}

if (support.blob) {
  this.blob = function() {
    var rejected = consumed(this)
    if (rejected) {
      return rejected
    }

    if (this._bodyBlob) {
      return Promise.resolve(this._bodyBlob)
    } else if (this._bodyArrayBuffer) {
      return Promise.resolve(new Blob([this._bodyArrayBuffer]))
    } else if (this._bodyFormData) {
      throw new Error('could not read FormData body as blob')
    } else {
      return Promise.resolve(new Blob([this._bodyText]))
    }
  }

  this.arrayBuffer = function() {
    if (this._bodyArrayBuffer) {
      return consumed(this) || Promise.resolve(this._bodyArrayBuffer)
    } else {
      return this.blob().then(readBlobAsArrayBuffer)
    }
  }
}

this.text = function() {
  var rejected = consumed(this)
  if (rejected) {
    return rejected
  }

  if (this._bodyBlob) {
    return readBlobAsText(this._bodyBlob)
  } else if (this._bodyArrayBuffer) {
    return Promise.resolve(readArrayBufferAsText(this._bodyArrayBuffer))
  } else if (this._bodyFormData) {
    throw new Error('could not read FormData body as text')
  } else {
    return Promise.resolve(this._bodyText)
  }
}

if (support.formData) {
  this.formData = function() {
    return this.text().then(decode)
  }
}

this.json = function() {
  return this.text().then(JSON.parse)
}

return this
}

// HTTP methods whose capitalization should be normalized
var methods = ['DELETE', 'GET', 'HEAD', 'OPTIONS', 'POST', 'PUT']

function normalizeMethod(method) {
var upcased = method.toUpperCase()
return (methods.indexOf(upcased) > -1) ? upcased : method
}

function Request(input, options) {
options = options || {}
var body = options.body

if (typeof input === 'string') {
  this.url = input
} else {
  if (input.bodyUsed) {
    throw new TypeError('Already read')
  }
  this.url = input.url
  this.credentials = input.credentials
  if (!options.headers) {
    this.headers = new Headers(input.headers)
  }
  this.method = input.method
  this.mode = input.mode
  if (!body && input._bodyInit != null) {
    body = input._bodyInit
    input.bodyUsed = true
  }
}

this.credentials = options.credentials || this.credentials || 'omit'
if (options.headers || !this.headers) {
  this.headers = new Headers(options.headers)
}
this.method = normalizeMethod(options.method || this.method || 'GET')
this.mode = options.mode || this.mode || null
this.referrer = null

if ((this.method === 'GET' || this.method === 'HEAD') && body) {
  throw new TypeError('Body not allowed for GET or HEAD requests')
}
this._initBody(body)
}

Request.prototype.clone = function() {
return new Request(this, { body: this._bodyInit })
}

function decode(body) {
var form = new FormData()
body.trim().split('&').forEach(function(bytes) {
  if (bytes) {
    var split = bytes.split('=')
    var name = split.shift().replace(/\+/g, ' ')
    var value = split.join('=').replace(/\+/g, ' ')
    form.append(decodeURIComponent(name), decodeURIComponent(value))
  }
})
return form
}

function parseHeaders(rawHeaders) {
var headers = new Headers()
rawHeaders.split('\r\n').forEach(function(line) {
  var parts = line.split(':')
  var key = parts.shift().trim()
  if (key) {
    var value = parts.join(':').trim()
    headers.append(key, value)
  }
})
return headers
}

Body.call(Request.prototype)

function Response(bodyInit, options) {
if (!options) {
  options = {}
}

this.type = 'default'
this.status = 'status' in options ? options.status : 200
this.ok = this.status >= 200 && this.status < 300
this.statusText = 'statusText' in options ? options.statusText : 'OK'
this.headers = new Headers(options.headers)
this.url = options.url || ''
this._initBody(bodyInit)
}

Body.call(Response.prototype)

Response.prototype.clone = function() {
return new Response(this._bodyInit, {
  status: this.status,
  statusText: this.statusText,
  headers: new Headers(this.headers),
  url: this.url
})
}

Response.error = function() {
var response = new Response(null, {status: 0, statusText: ''})
response.type = 'error'
return response
}

var redirectStatuses = [301, 302, 303, 307, 308]

Response.redirect = function(url, status) {
if (redirectStatuses.indexOf(status) === -1) {
  throw new RangeError('Invalid status code')
}

return new Response(null, {status: status, headers: {location: url}})
}

self.Headers = Headers
self.Request = Request
self.Response = Response

self.fetch = function(input, init) {
return new Promise(function(resolve, reject) {
  var request = new Request(input, init)
  var xhr = new XMLHttpRequest()

  xhr.onload = function() {
    var options = {
      status: xhr.status,
      statusText: xhr.statusText,
      headers: parseHeaders(xhr.getAllResponseHeaders() || '')
    }
    options.url = 'responseURL' in xhr ? xhr.responseURL :    options.headers.get('X-Request-URL')
    var body = 'response' in xhr ? xhr.response : xhr.responseText
    resolve(new Response(body, options))
  }

  xhr.onerror = function() {
    reject(new TypeError('Network request failed'))
  }

  xhr.ontimeout = function() {
    reject(new TypeError('Network request failed'))
  }

  xhr.open(request.method, request.url, true)

  if (request.credentials === 'include') {
    xhr.withCredentials = true
  }

  if ('responseType' in xhr && support.blob) {
    xhr.responseType = 'blob'
  }

  request.headers.forEach(function(value, name) {
    xhr.setRequestHeader(name, value)
  })

  xhr.send(typeof request._bodyInit === 'undefined' ? null :  request._bodyInit)
})
}
self.fetch.polyfill = true
})(typeof self !== 'undefined' ? self : this);

Answer 1

Try bindind the function:

constructor(props) {
  super(props)

  this.state = {
    name: '', 
    description: '',
    isLoading: false
  }

  this._getRandomBrewdogWithFeedback  = this._getRandomBrewdogWithFeedback.bind(this);
}

_getRandomBrewdogWithFeedback () {
  //this.setState({ isLoading: true }); 
  // You cannot be sure here that these two lines of code will be executed
  // in the order you think since setState is an async method.
  // I guess what you should do is to pass a callback to setState with the code below

  this.setState({ isLoading: true }, () => {
    //This is the only way to ensure that state has changed
    //before calling the API
    getRandomBrewdog()
      .then(json => this.setState({
        name: json.name,
        description: json.description,
        isLoading: false // la requête est terminée
      }))
      .catch(error => console.error(error))
  })
}

componentWillMount() {
  this._getRandomBrewdogWithFeedback();
}

If you dont bind the function, when you call this inside _getRandomBrewdogWithFeedback you're not really referencing to the component. In fact, you can check that by debugging.

Let me know if it works, if not, point in the code where exactly is the error being thrown.

For more information about binding, take a look here

NOTE: I also added a comment related to how you are using setState in componentDidMount . Pay attention to that, It could be painful to realize about that kind of misbehaviors

NOTE 2: I'm using diferently fetch function, such this way:

fetch(...)
  .then((response) => {
    if (response.ok) {
      return response.json()
        .then((responseData) => {
          return responseData;
        });
    }

    return response.json().
      then((error) => {
        console.log(error);
        return Promise.reject(error);
      });
  })

**Note: ** you are using getRandomBrewdog as if it was returning a promise, but it is not.

Changing the definition of the function should solve the problem:

getRandomBrewdog = () => {
  return fetch.then(...)
}

---

ANSWER :

The json flow is a tab, in v1 it wasn't -->

It works with this code ->response[0], it doesn't work with response or json() or response.json() :

  export const getRandomBrewdog = () => 
   fetch(${rootEndpoint}/beers/random, {headers})
    .then(function(response) 
    {if(response.status == 200) 
     return   response.json(); 
    else throw new Error('Something went wrong on api server!'); })
    .then (function(response) { 
     return response[0]; }) 
   .catch(function(error) { console.error (error); });