# App won't connect to backend
**URL:** https://forum.codewithmosh.com/t/app-wont-connect-to-backend/7898
**Category:** React Native
**Created:** [October 12, 2021, 12:49pm UTC](https://forum.codewithmosh.com/t/app-wont-connect-to-backend/7898 "2021-10-12T12:49:10Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@bebo7](https://forum.codewithmosh.com/u/bebo7)
#### Post date: [October 12, 2021, 12:49pm UTC](https://forum.codewithmosh.com/t/app-wont-connect-to-backend/7898/1 "2021-10-12T12:49:10Z")
The backend works fine but the app fails to load response data.
Code from ListingScreen.js:
```auto
const [listings, setListings] = useState([]);
const [error, setError] = useState( false );
useEffect( () => {
loadListings();
}, [] );
const loadListings = async () => {
const response = await listingsApi.getListings();
if ( !response.ok ) return setError( true );
setError( false );
setListings( response.data );
};
```
---
### Author:  [@Justly](https://forum.codewithmosh.com/u/Justly)
#### Post date: [October 15, 2021, 7:58am UTC](https://forum.codewithmosh.com/t/app-wont-connect-to-backend/7898/2 "2021-10-15T07:58:53Z")
Hey.
I just wanted to know if you didn’t not use localhost when setting your assetsBaseUrl
---
### Author:  [@bebo7](https://forum.codewithmosh.com/u/bebo7)
#### Post date: [October 15, 2021, 9:17am UTC](https://forum.codewithmosh.com/t/app-wont-connect-to-backend/7898/3 "2021-10-15T09:17:17Z")
I used my IP like mosh told us to do, followed every step and rechecked everything I think. Even tried both IP4 and IP6.
---
### Author:  [@sufian.babri](https://forum.codewithmosh.com/u/sufian.babri)
#### Post date: [October 18, 2021, 10:56am UTC](https://forum.codewithmosh.com/t/app-wont-connect-to-backend/7898/4 "2021-10-18T10:56:35Z")
You probably need to debug the code inside your `listingsApi.getListings()`. Knowing the error will help us know more about the issue.
---
### Author:  [@bebo7](https://forum.codewithmosh.com/u/bebo7)
#### Post date: [October 19, 2021, 5:21pm UTC](https://forum.codewithmosh.com/t/app-wont-connect-to-backend/7898/5 "2021-10-19T17:21:31Z")
My debug dosent really work as it should. Port 19001 yields nothing. I get some response from 19000, but all I can gather is that listings “Failed to load response data”. But I already knew that. Because I can load the listings in my browser, althoug it looks different from the video.
---
### Author:  [@sufian.babri](https://forum.codewithmosh.com/u/sufian.babri)
#### Post date: [October 19, 2021, 6:42pm UTC](https://forum.codewithmosh.com/t/app-wont-connect-to-backend/7898/6 "2021-10-19T18:42:06Z")
Can you post the code that is inside `getListings() `.
I assume it has a line like this below:
```auto
if (res.status === 200)
```
Before this line you need to add this and show us the output `console.log(res);`
---
### Author:  [@bebo7](https://forum.codewithmosh.com/u/bebo7)
#### Post date: [October 23, 2021, 12:29pm UTC](https://forum.codewithmosh.com/t/app-wont-connect-to-backend/7898/7 "2021-10-23T12:29:43Z")
development.json
```auto
{
"assetsBaseUrl": "http://[ip address]/assets/",
"port": 9000
}
```
My api/listings.js
```auto
import client from './client';
const endpoint = '/listings'; // Also tried './listings'
const getListings = () => client.get( endpoint );
export default {
getListings,
};
```
My api/client.js
```auto
import { create } from 'apisauce';
const apiClient = create({
baseURL: 'http://[ip address]/api',
});
export default apiClient;
```
My ListingsScreen.jsx
```auto
import React, { useEffect, useState } from 'react';
import { ... } from 'react-native';
{ ... } // Various imports
import listingsApi from '../api/listings';
import routes from '../navigation/routes';
function ListingsScreen({ navigation }) {
const [listings, setListings] = useState([]);
const [error, setError] = useState( false );
useEffect( () => {
loadListings();
}, [] );
const loadListings = async () => {
const response = await listingsApi.getListings();
if ( !response.ok ) return setError( true );
setError( false );
setListings( response.data );
};
return (
{
error &&
Couldn't retrive the listings.
}
listing.id.toString() }
renderItem={ ({item}) => (
navigation.navigate( routes.LISTING_DETAILS, item )}
/>
)}
/>
);
}
const styles = StyleSheet.create({ ... });
export default ListingsScreen;
```
Your code I don’t recognize from the course.
---
### Author:  [@sufian.babri](https://forum.codewithmosh.com/u/sufian.babri)
#### Post date: [October 23, 2021, 2:08pm UTC](https://forum.codewithmosh.com/t/app-wont-connect-to-backend/7898/8 "2021-10-23T14:08:59Z")
Replace the code below:
```auto
if ( !response.ok ) return setError( true );
```
With:
```auto
if ( !response.ok ) {
console.log(response);
return setError( true );
}
```
Now in your console you will see the actual error which is failing the API call.
---
### Author:  [@bebo7](https://forum.codewithmosh.com/u/bebo7)
#### Post date: [October 25, 2021, 9:43am UTC](https://forum.codewithmosh.com/t/app-wont-connect-to-backend/7898/9 "2021-10-25T09:43:23Z")
`This is the only error in the console. The only thing I can gather from this is that I can’t connect to the backend or the backend returns undefined
```auto
TypeError: Cannot read property 'toString' of undefined
This error is located at:
in VirtualizedList (at FlatList.js:624)
in FlatList (at ListingsScreen.jsx:44)
in RCTView (at View.js:34)
in View (at Screen.jsx:12)
in RCTSafeAreaView (at SafeAreaView.js:51)
in ForwardRef(SafeAreaView) (at Screen.jsx:11)
in Screen (at ListingsScreen.jsx:37)
in ListingsScreen (at SceneView.tsx:122)
in StaticContainer
in StaticContainer (at SceneView.tsx:115)
in EnsureSingleNavigator (at SceneView.tsx:114)
in SceneView (at useDescriptors.tsx:153)
in RCTView (at View.js:34)
in View (at CardContainer.tsx:245)
in RCTView (at View.js:34)
in View (at CardContainer.tsx:244)
in RCTView (at View.js:34)
in View (at CardSheet.tsx:33)
in ForwardRef(CardSheet) (at Card.tsx:573)
in RCTView (at View.js:34)
in View (at createAnimatedComponent.js:165)
in AnimatedComponent (at createAnimatedComponent.js:215)
in ForwardRef(AnimatedComponentWrapper) (at Card.tsx:555)
in PanGestureHandler (at GestureHandlerNative.tsx:13)
in PanGestureHandler (at Card.tsx:549)
in RCTView (at View.js:34)
in View (at createAnimatedComponent.js:165)
in AnimatedComponent (at createAnimatedComponent.js:215)
in ForwardRef(AnimatedComponentWrapper) (at Card.tsx:544)
in RCTView (at View.js:34)
in View (at Card.tsx:538)
in Card (at CardContainer.tsx:206)
in CardContainer (at CardStack.tsx:623)
in RCTView (at View.js:34)
in View (at Screens.tsx:84)
in MaybeScreen (at CardStack.tsx:616)
in RCTView (at View.js:34)
in View (at Screens.tsx:54)
in MaybeScreenContainer (at CardStack.tsx:498)
in CardStack (at StackView.tsx:462)
in KeyboardManager (at StackView.tsx:458)
in SafeAreaProviderCompat (at StackView.tsx:455)
in RCTView (at View.js:34)
in View (at StackView.tsx:454)
in StackView (at createStackNavigator.tsx:87)
in StackNavigator (at FeedNavigator.jsx:11)
in FeedNavigator (at SceneView.tsx:122)
in StaticContainer
in StaticContainer (at SceneView.tsx:115)
in EnsureSingleNavigator (at SceneView.tsx:114)
in SceneView (at useDescriptors.tsx:153)
in RCTView (at View.js:34)
in View (at BottomTabView.tsx:55)
in SceneContent (at BottomTabView.tsx:172)
in RCTView (at View.js:34)
in View (at ResourceSavingScene.tsx:68)
in RCTView (at View.js:34)
in View (at ResourceSavingScene.tsx:63)
in ResourceSavingScene (at BottomTabView.tsx:166)
in RCTView (at View.js:34)
in View (at src/index.native.js:123)
in ScreenContainer (at BottomTabView.tsx:146)
in RNCSafeAreaProvider (at SafeAreaContext.tsx:74)
in SafeAreaProvider (at SafeAreaProviderCompat.tsx:42)
in SafeAreaProviderCompat (at BottomTabView.tsx:145)
in BottomTabView (at createBottomTabNavigator.tsx:45)
in BottomTabNavigator (at AppNavigator.jsx:14)
in AppNavigator (at App.js:14)
in EnsureSingleNavigator (at BaseNavigationContainer.tsx:409)
in ForwardRef(BaseNavigationContainer) (at NavigationContainer.tsx:91)
in ThemeProvider (at NavigationContainer.tsx:90)
in ForwardRef(NavigationContainer) (at App.js:13)
in App (created by ExpoRoot)
in ExpoRoot (at renderApplication.js:45)
in RCTView (at View.js:34)
in View (at AppContainer.js:106)
in DevAppContainer (at AppContainer.js:121)
in RCTView (at View.js:34)
in View (at AppContainer.js:132)
in AppContainer (at renderApplication.js:39)
at node_modules\expo\build\logs\LogSerialization.js:160:14 in _captureConsoleStackTrace
at node_modules\expo\build\logs\LogSerialization.js:41:26 in serializeLogDataAsync
- ... 9 more stack frames from framework internals
[Unhandled promise rejection: TypeError: Cannot read property 'toString' of undefined]
at app\screens\ListingsScreen.jsx:46:30 in FlatList.props.keyExtractor
at node_modules\react-native\Libraries\Lists\FlatList.js:519:13 in _keyExtractor
at node_modules\react-native\Libraries\Lists\VirtualizedList.js:894:18 in _pushCells
- ... 8 more stack frames from framework internals
```
---
### Author:  [@sufian.babri](https://forum.codewithmosh.com/u/sufian.babri)
#### Post date: [October 25, 2021, 10:49am UTC](https://forum.codewithmosh.com/t/app-wont-connect-to-backend/7898/10 "2021-10-25T10:49:27Z")
It looks like you have a variable at line 44 of ListingsScreen.jsx on which you’re calling `toString`, while its value is undefined.
If this doesn’t help, can you upload your code somewhere (preferably github)? To make the upload quick, just make sure you aren’t committing or uploading the **node\_modules** folder.
Actually I haven’t bought this specific course but I am an experienced React/React Native developer and could help you I have access to the code.
---
### Author:  [@bebo7](https://forum.codewithmosh.com/u/bebo7)
#### Post date: [October 30, 2021, 8:49pm UTC](https://forum.codewithmosh.com/t/app-wont-connect-to-backend/7898/11 "2021-10-30T20:49:49Z")
Line 44 works exactly as intended. Where the problem is is that getListings fetches an undefined variable instead of the json object from the backend Mosh provided. Every line is identical to the one in the course. this I’m sure of becuase I’ve tripple checked twice. I can upload my code somewhere if you really need me to. But every relevant piece of code I’ve already provided. Except from the backend which Mosh created. I’m honestly at a loss for what to do.
Edit: The previous error has just been magicaly resolved and the response have been logged in the console.
```auto
{duration: 2134, problem: "NETWORK_ERROR", originalError: Error: Network Error
at createError (http://[ip address]:19000/node_modules%5Cexpo%5CAppEntry.…, ok: false, status: null, …}
config:
adapter: ƒ xhrAdapter(config)
baseURL: "http://[ip address]/api"
data: undefined
headers: {Accept: "application/json"}
maxBodyLength: -1
maxContentLength: -1
method: "get"
params: {}
timeout: 0
transformRequest: [ƒ]
transformResponse: [ƒ]
transitional: {silentJSONParsing: true, forcedJSONParsing: true, clarifyTimeoutError: false}
url: "/listings"
validateStatus: ƒ validateStatus(status)
xsrfCookieName: "XSRF-TOKEN"
xsrfHeaderName: "X-XSRF-TOKEN"
__proto__ : Object
data: null
duration: 2134
headers: null
ok: false
originalError: Error: Network Error at createError (http://[ip address]:19000/node_modules%5Cexpo%5CAppEntry.bundle?platform=ios&dev=true&hot=false&minify=false:168819:17) at XMLHttpRequest.handleError (http://[ip address]:19000/node_modules%5Cexpo%5CAppEntry.bundle?platform=ios&dev=true&hot=false&minify=false:168729:16)
problem: "NETWORK_ERROR"
status: null
__proto__ : Object
```
response.problem returns NETWORK\_ERROR
---
### Author:  [@sufian.babri](https://forum.codewithmosh.com/u/sufian.babri)
#### Post date: [October 31, 2021, 4:50am UTC](https://forum.codewithmosh.com/t/app-wont-connect-to-backend/7898/12 "2021-10-31T04:50:35Z")
Have you tried putting your actual ip address in the code?
In case putting you local ip address doesn’t work (which is in a form of 192.168.x.y, where x and y are numbers), try putting the ip address you get from [https://whatismyipaddress.com/](https://whatismyipaddress.com/)
If it doesn’t work either, you can upload the source code at Github (public repo) and share the link of the repo here. I will take a look at it.
---
### Author:  [@bebo7](https://forum.codewithmosh.com/u/bebo7)
#### Post date: [October 31, 2021, 9:46am UTC](https://forum.codewithmosh.com/t/app-wont-connect-to-backend/7898/13 "2021-10-31T09:46:18Z")
[ip address] is just a placeholder to hide my ip. I’ve tried localhost, IP4 and IP6 numerous times. I’ve fetched my IP4 from your link and from my computers settings. When I used the address provided by [whatismyipaddress.com](http://whatismyipaddress.com) I got the toString error and localhost, IP6 and the IP4 provided by settings\>network\>wifi just returned the NETWORK\_ERROR string.
It seems to me that the later is the most telling error because it is an error documented by apisauce so the question is what it exactly means and how to fix a network errror.
Do you need the backend aswell or only the code I’ve written?
---
### Author:  [@sufian.babri](https://forum.codewithmosh.com/u/sufian.babri)
#### Post date: [October 31, 2021, 6:15pm UTC](https://forum.codewithmosh.com/t/app-wont-connect-to-backend/7898/14 "2021-10-31T18:15:12Z")
Upload both the frontend and backend source code please.
---
### Author:  [@morfix98](https://forum.codewithmosh.com/u/morfix98)
#### Post date: [November 21, 2021, 1:06pm UTC](https://forum.codewithmosh.com/t/app-wont-connect-to-backend/7898/15 "2021-11-21T13:06:18Z")
Was this resolved? I’m having the same issue.
---
### Author:  [@Shaikh123](https://forum.codewithmosh.com/u/Shaikh123)
#### Post date: [December 30, 2021, 8:37pm UTC](https://forum.codewithmosh.com/t/app-wont-connect-to-backend/7898/16 "2021-12-30T20:37:03Z")
well we need to activate the backend but the problem comes when we run the server it returns a
no module found-express here is what it came for me
```auto
node:internal/modules/cjs/loader:936
throw err;
^
Error: Cannot find module 'express'
Require stack:
- C:\Users\iftkh\app\Backend\index.js
at Function.Module._resolveFilename (node:internal/modules/cjs/loader:933:15)
at Function.Module._load (node:internal/modules/cjs/loader:778:27)
at Module.require (node:internal/modules/cjs/loader:1005:19)
at require (node:internal/modules/cjs/helpers:102:18)
at Object. (C:\Users\iftkh\app\Backend\index.js:1:17)
at Module._compile (node:internal/modules/cjs/loader:1101:14)
at Object.Module._extensions..js (node:internal/modules/cjs/loader:1153:10)
at Module.load (node:internal/modules/cjs/loader:981:32)
at Function.Module._load (node:internal/modules/cjs/loader:822:12)
at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:81:12) {
code: 'MODULE_NOT_FOUND',
requireStack: ['C:\\Users\\iftkh\\app\\Backend\\index.js']
}
```
---
### Author:  [@sufian.babri](https://forum.codewithmosh.com/u/sufian.babri)
#### Post date: [January 4, 2022, 4:28pm UTC](https://forum.codewithmosh.com/t/app-wont-connect-to-backend/7898/17 "2022-01-04T16:28:02Z")
I think you need to run `npm install` from your server’s folder before starting itYour server should now run.
---
### Author:  [@Icabina](https://forum.codewithmosh.com/u/Icabina)
#### Post date: [January 14, 2022, 11:15pm UTC](https://forum.codewithmosh.com/t/app-wont-connect-to-backend/7898/19 "2022-01-14T23:15:09Z")
(post deleted by author)
---
### Author:  [@Icabina](https://forum.codewithmosh.com/u/Icabina)
#### Post date: [January 14, 2022, 11:15pm UTC](https://forum.codewithmosh.com/t/app-wont-connect-to-backend/7898/20 "2022-01-14T23:15:48Z")
(post deleted by author)
---
### Author:  [@bebo7](https://forum.codewithmosh.com/u/bebo7)
#### Post date: [January 20, 2022, 12:56pm UTC](https://forum.codewithmosh.com/t/app-wont-connect-to-backend/7898/22 "2022-01-20T12:56:16Z")
I’m sorry for late answer. Exams and christmas and shit you know.
Backend and app folder, app.js and app.json. The whole projct with packages would take too much space.
> **[GitHub - bebo7/Mosh-courses-help](https://github.com/bebo7/Mosh-courses-help)**
>
> Contribute to bebo7/Mosh-courses-help development by creating an account on GitHub.
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