Develop Reference

React: TypeError Cannot read properties of undefined (reading '0')

I am working on a React App, and i'm trying to get some data using an axios GET request from my node backend.
the Api Endpoint i'm currently using that regard this problem is the following:
// NodeJS Backend
app.get('/v1/companys/user/:user_uuid', verify, (req, res) => { // GET - Company by User UUID
const selectQuery = 'SELECT * FROM companys WHERE uuid = (SELECT company_uuid FROM users WHERE uuid = ?)';
connection.query(selectQuery, [req.params.user_uuid], (err, results) => {
if(err) {
res.send(err)
} else if (results.length === 0) {
res.json({status: 404, message: 'Company not found'})
} else {
res.json({data: results})
}
});
});
This is my Front End:
// ReactJS FrontEnd
const companyLogo = userCompany ? userCompany.logo_url : null;
console.log(userCompany);
useEffect(() => {
const getUserCompany = async () => {
try {
await axios.get(process.env.REACT_APP_API_URL + 'companys/user/' + userUuid).then((response) => {
console.log("response "+ response);
let res = response.data.data[0];
console.log(res);
setUserCompany(res);
});
} catch (error) {
console.log(error);
}
};
getUserCompany();
}, [userUuid]);
There app works fine, but on the console the following error appear:
The object below the error is in fact the thing that i need (companyLogo)
I was wondering if someone know what am I doing wrong on my frontend to fix the TypeError.
Thanks for the help!

If you use optional chaining (?.) to catch possible null/undefined values, you'll most likely fix the issue.
So like this: let res = response.data.data?.[0];

The reason of ERR_HTTP_HEADERS_SENT error in Express.js middleware

I have created middleware to validate fields in body, here is how it looks like:
Front-end route:
router.post('/s-i', async (req, res) => {
try {
const { data } = await api.post('/sign-in', req.body)
res.cookie("_rt", data._rt, { httpOnly: true, secure: false })
delete data._rt
return res.json(data)
} catch (e) {
// Here is error
return res.status(e.response.status).json(e.response.data)
}
});
Route (back-end):
router.post('/sign-in', v(['email', 'password', 'twoFa', 'phone']), wrapAsync(userController.signIn));
Middleware:
exports.v = fields => {
return (req, res, next) => {
fields.forEach(field => {
if (req.body[field]) {
const result = require(`./validators/${field}`)(req.body[field])
if (!result)
return res.status(400).json({ message: 'bad-request', status: 400 })
}
})
next()
}
}
In the place where comment is placed I can see this error, actually, everything works find, and if there is wrong field in body front will receive 400 status code, but in back-end terminal I still have this error and can't get why.
The problem is I still keep getting this ERR_HTTP_HEADERS_SENT error. I know the reason of this problem - for example - if you are trying do res.send({}) twice, but I don't really see the reason of problem in this case.

The return res.status(400)... statement returns only from the inner function fields.forEach(field => {...}), but you must return from the middleware function, otherwise the next() will invoke subsequent middlewares after the .json output, leading to the observed error.
You can achieve this by replacing fields.forEach(field => {...}) with
for (var field of fields) {
if (req.body[field]) {
const result = require(`./validators/${field}`)(req.body[field])
if (!result)
return res.status(400).json({ message: 'bad-request', status: 400 })
}
}

How do I listen for new uploads from a specific channel in the YouTube API?

I am making a Discord bot, and I want it to be able to use the YouTube API to fetch new uploads from a specific channel.
I have searched elsewhere, but they all say how to upload videos, not how to track uploads.
Is this possible, and how can I do it?
Edit: Tried PubSubHubbub but it was very confusing and I couldn't get it to work

Here an example built on top of Node.js (v12) and Fastify and published with ngrok:
I wrote some comments explaining what it is happening:
const fastify = require('fastify')({ logger: true })
const xmlParser = require('fast-xml-parser')
const { URLSearchParams } = require('url')
const fetch = require('node-fetch')
// add an xml parser
fastify.addContentTypeParser('application/atom+xml', { parseAs: 'string' }, function (req, xmlString, done) {
try {
const body = xmlParser.parse(xmlString, {
attributeNamePrefix: '',
ignoreAttributes: false
})
done(null, body)
} catch (error) {
done(error)
}
})
// this endpoint needs for authentication
fastify.get('/', (request, reply) => {
reply.send(request.query['hub.challenge'])
})
// this endpoint will get the updates
fastify.post('/', (request, reply) => {
console.log(JSON.stringify(request.body, null, 2))
reply.code(204)
reply.send('ok')
})
fastify.listen(8080)
.then(() => {
// after the server has started, subscribe to the hub
// Parameter list: https://pubsubhubbub.github.io/PubSubHubbub/pubsubhubbub-core-0.4.html#rfc.section.5.1
const params = new URLSearchParams()
params.append('hub.callback', 'https://1f3dd0c63e78.ngrok.io') // you must have a public endpoint. get it with "ngrok http 8080"
params.append('hub.mode', 'subscribe')
params.append('hub.topic', 'https://www.youtube.com/xml/feeds/videos.xml?channel_id=UCfWbGF64qBSVM2Wq9fwrfrg')
params.append('hub.lease_seconds', '')
params.append('hub.secret', '')
params.append('hub.verify', 'sync')
params.append('hub.verify_token', '')
return fetch('https://pubsubhubbub.appspot.com/subscribe', {
headers: { 'content-type': 'application/x-www-form-urlencoded' },
body: params,
method: 'POST'
})
})
.then((res) => {
console.log(`The status must be 204. Received ${res.status}`)
// shows the error if something went wrong
if (res.status !== 204) {
return res.text().then(txt => console.log(txt))
}
})
I used my channel id to do some testing, consider that the notification is not in real-time, the POSTs are triggered after several minutes usually.

How can you use axios interceptors?

I have seen axios documentation, but all it says is
// 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);
});
Also many tutorials only show this code but I am confused what it is used for, can someone please give me simple example to follow.

To talk in simple terms, it is more of a checkpoint for every HTTP action. Every API call that has been made, is passed through this interceptor.
So, why two interceptors?
An API call is made up of two halves, a request, and a response. Since it behaves like a checkpoint, the request and the response have separate interceptors.
Some request interceptor use cases -
Assume you want to check before making a request if your credentials are valid. So, instead of actually making an API call, you can check at the interceptor level that your credentials are valid.
Assume you need to attach a token to every request made, instead of duplicating the token addition logic at every Axios call, you can make an interceptor that attaches a token on every request that is made.
Some response interceptor use cases -
Assume you got a response, and judging by the API responses you want to deduce that the user is logged in. So, in the response interceptor, you can initialize a class that handles the user logged in state and update it accordingly on the response object you received.
Assume you have requested some API with valid API credentials, but you do not have the valid role to access the data. So, you can trigger an alert from the response interceptor saying that the user is not allowed. This way you'll be saved from the unauthorized API error handling that you would have to perform on every Axios request that you made.
Here are some code examples
The request interceptor
One can print the configuration object of axios (if need be) by doing (in this case, by checking the environment variable):
const DEBUG = process.env.NODE_ENV === "development";
axios.interceptors.request.use((config) => {
/** In dev, intercepts request and logs it into console for dev */
if (DEBUG) { console.info("✉️ ", config); }
return config;
}, (error) => {
if (DEBUG) { console.error("✉️ ", error); }
return Promise.reject(error);
});
If one wants to check what headers are being passed/add any more generic headers, it is available in the config.headers object. For example:
axios.interceptors.request.use((config) => {
config.headers.genericKey = "someGenericValue";
return config;
}, (error) => {
return Promise.reject(error);
});
In case it's a GET request, the query parameters being sent can be found in config.params object.
The response interceptor
You can even optionally parse the API response at the interceptor level and pass the parsed response down instead of the original response. It might save you the time of writing the parsing logic again and again in case the API is used in the same way in multiple places. One way to do that is by passing an extra parameter in the api-request and use the same parameter in the response interceptor to perform your action. For example:
//Assume we pass an extra parameter "parse: true"
axios.get("/city-list", { parse: true });
Once, in the response interceptor, we can use it like:
axios.interceptors.response.use((response) => {
if (response.config.parse) {
//perform the manipulation here and change the response object
}
return response;
}, (error) => {
return Promise.reject(error.message);
});
So, in this case, whenever there is a parse object in response.config, the manipulation is done, for the rest of the cases, it'll work as-is.
You can even view the arriving HTTP codes and then make the decision. For example:
axios.interceptors.response.use((response) => {
if(response.status === 401) {
alert("You are not authorized");
}
return response;
}, (error) => {
if (error.response && error.response.data) {
return Promise.reject(error.response.data);
}
return Promise.reject(error.message);
});

You can use this code for example, if you want to catch the time that takes from the moment that the request was sent until the moment you received the response:
const axios = require("axios");
(async () => {
axios.interceptors.request.use(
function (req) {
req.time = { startTime: new Date() };
return req;
},
(err) => {
return Promise.reject(err);
}
);
axios.interceptors.response.use(
function (res) {
res.config.time.endTime = new Date();
res.duration =
res.config.time.endTime - res.config.time.startTime;
return res;
},
(err) => {
return Promise.reject(err);
}
);
axios
.get("http://localhost:3000")
.then((res) => {
console.log(res.duration)
})
.catch((err) => {
console.log(err);
});
})();

It is like a middle-ware, basically it is added on any request (be it GET, POST, PUT, DELETE) or on any response (the response you get from the server).
It is often used for cases where authorisation is involved.
Have a look at this: Axios interceptors and asynchronous login
Here is another article about this, with a different example: https://medium.com/#danielalvidrez/handling-error-responses-with-grace-b6fd3c5886f0
So the gist of one of the examples is that you could use interceptor to detect if your authorisation token is expired ( if you get 403 for example ) and to redirect the page.

I will give you more practical use-case which I used in my real world projects. I usually use, request interceptor for token related staff (accessToken, refreshToken), e.g., whether token is not expired, if so, then update it with refreshToken and hold all other calls until it resolves. But what I like most is axios response interceptors where you can put your apps global error handling logic like below:
httpClient.interceptors.response.use(
(response: AxiosResponse) => {
// Any status code that lie within the range of 2xx cause this function to trigger
return response.data;
},
(err: AxiosError) => {
// Any status codes that falls outside the range of 2xx cause this function to trigger
const status = err.response?.status || 500;
// we can handle global errors here
switch (status) {
// authentication (token related issues)
case 401: {
return Promise.reject(new APIError(err.message, 409));
}
// forbidden (permission related issues)
case 403: {
return Promise.reject(new APIError(err.message, 409));
}
// bad request
case 400: {
return Promise.reject(new APIError(err.message, 400));
}
// not found
case 404: {
return Promise.reject(new APIError(err.message, 404));
}
// conflict
case 409: {
return Promise.reject(new APIError(err.message, 409));
}
// unprocessable
case 422: {
return Promise.reject(new APIError(err.message, 422));
}
// generic api error (server related) unexpected
default: {
return Promise.reject(new APIError(err.message, 500));
}
}
}
);

How about this. You create a new Axios instance and attach an interceptor to it. Then you can use that interceptor anywhere in your app
export const axiosAuth = axios.create()
//we intercept every requests
axiosAuth.interceptors.request.use(async function(config){
//anything you want to attach to the requests such as token
return config;
}, error => {
return Promise.reject(error)
})
//we intercept every response
axiosAuth.interceptors.request.use(async function(config){
return config;
}, error => {
//check for authentication or anything like that
return Promise.reject(error)
})
Then you use axiosAuth the same way you use axios

This is the way I used to do in my project. The code snippet refers how to use access and refresh token in the axios interceptors and will help to implements refresh token functionalities.
const API_URL =
process.env.NODE_ENV === 'development'
? 'http://localhost:8080/admin/api'
: '/admin-app/admin/api';
const Service = axios.create({
baseURL: API_URL,
headers: {
Accept: 'application/json',
},
});
Service.interceptors.request.use(
config => {
const accessToken = localStorage.getItem('accessToken');
if (accessToken) {
config.headers.common = { Authorization: `Bearer ${accessToken}` };
}
return config;
},
error => {
Promise.reject(error.response || error.message);
}
);
Service.interceptors.response.use(
response => {
return response;
},
error => {
let originalRequest = error.config;
let refreshToken = localStorage.getItem('refreshToken');
const username = EmailDecoder(); // decode email from jwt token subject
if (
refreshToken &&
error.response.status === 403 &&
!originalRequest._retry &&
username
) {
originalRequest._retry = true;
return axios
.post(`${API_URL}/authentication/refresh`, {
refreshToken: refreshToken,
username,
})
.then(res => {
if (res.status === 200) {
localStorage.setItem(
'accessToken',
res.data.accessToken
);
localStorage.setItem(
'refreshToken',
res.data.refreshToken
);
originalRequest.headers[
'Authorization'
] = `Bearer ${res.data.accessToken}`;
return axios(originalRequest);
}
})
.catch(() => {
localStorage.clear();
location.reload();
});
}
return Promise.reject(error.response || error.message);
}
);
export default Service;

I have implemented in the following way
httpConfig.js
import axios from 'axios'
import { baseURL } from '../utils/config'
import { SetupInterceptors } from './SetupInterceptors'
const http = axios.create({
baseURL: baseURL
})
SetupInterceptors(http)
export default http
SetupInterceptors.js
import { baseURL } from '../utils/config'
export const SetupInterceptors = http => {
http.interceptors.request.use(
config => {
config.headers['token'] = `${localStorage.getItem('token')}`
config.headers['content-type'] = 'application/json'
return config
},
error => {
return Promise.reject(error)
}
)
http.interceptors.response.use(function(response) {
return response
}, function (error) {
const status = error?.response?.status || 0
const resBaseURL = error?.response?.config?.baseURL
if (resBaseURL === baseURL && status === 401) {
if (localStorage.getItem('token')) {
localStorage.clear()
window.location.assign('/')
return Promise.reject(error)
} else {
return Promise.reject(error)
}
}
return Promise.reject(error)
})
}
export default SetupInterceptors
Reference : link

Axios Interceptors retry original request and access original promise

I have an interceptor in place to catch 401 errors if the access token expires. If it expires it tries the refresh token to get a new access token. If any other calls are made during this time they are queued until the access token is validated.
This is all working very well. However when processing the queue using Axios(originalRequest) the originally attached promises are not being called. See below for an example.
Working interceptor code:
Axios.interceptors.response.use(
response => response,
(error) => {
const status = error.response ? error.response.status : null
const originalRequest = error.config
if (status === 401) {
if (!store.state.auth.isRefreshing) {
store.dispatch('auth/refresh')
}
const retryOrigReq = store.dispatch('auth/subscribe', token => {
originalRequest.headers['Authorization'] = 'Bearer ' + token
Axios(originalRequest)
})
return retryOrigReq
} else {
return Promise.reject(error)
}
}
)
Refresh Method (Used the refresh token to get a new access token)
refresh ({ commit }) {
commit(types.REFRESHING, true)
Vue.$http.post('/login/refresh', {
refresh_token: store.getters['auth/refreshToken']
}).then(response => {
if (response.status === 401) {
store.dispatch('auth/reset')
store.dispatch('app/error', 'You have been logged out.')
} else {
commit(types.AUTH, {
access_token: response.data.access_token,
refresh_token: response.data.refresh_token
})
store.dispatch('auth/refreshed', response.data.access_token)
}
}).catch(() => {
store.dispatch('auth/reset')
store.dispatch('app/error', 'You have been logged out.')
})
},
Subscribe method in auth/actions module:
subscribe ({ commit }, request) {
commit(types.SUBSCRIBEREFRESH, request)
return request
},
As well as the Mutation:
[SUBSCRIBEREFRESH] (state, request) {
state.refreshSubscribers.push(request)
},
Here is a sample action:
Vue.$http.get('/users/' + rootState.auth.user.id + '/tasks').then(response => {
if (response && response.data) {
commit(types.NOTIFICATIONS, response.data || [])
}
})
If this request was added to the queue I because the refresh token had to access a new token I would like to attach the original then():
const retryOrigReq = store.dispatch('auth/subscribe', token => {
originalRequest.headers['Authorization'] = 'Bearer ' + token
// I would like to attache the original .then() as it contained critical functions to be called after the request was completed. Usually mutating a store etc...
Axios(originalRequest).then(//if then present attache here)
})
Once the access token has been refreshed the queue of requests is processed:
refreshed ({ commit }, token) {
commit(types.REFRESHING, false)
store.state.auth.refreshSubscribers.map(cb => cb(token))
commit(types.CLEARSUBSCRIBERS)
},

Update Feb 13, 2019
As many people have been showing an interest in this topic, I've created the axios-auth-refresh package which should help you to achieve behaviour specified here.
The key here is to return the correct Promise object, so you can use .then() for chaining. We can use Vuex's state for that. If the refresh call happens, we can not only set the refreshing state to true, we can also set the refreshing call to the one that's pending. This way using .then() will always be bound onto the right Promise object, and be executed when the Promise is done. Doing it so will ensure you don't need an extra queue for keeping the calls which are waiting for the token's refresh.
function refreshToken(store) {
if (store.state.auth.isRefreshing) {
return store.state.auth.refreshingCall;
}
store.commit('auth/setRefreshingState', true);
const refreshingCall = Axios.get('get token').then(({ data: { token } }) => {
store.commit('auth/setToken', token)
store.commit('auth/setRefreshingState', false);
store.commit('auth/setRefreshingCall', undefined);
return Promise.resolve(true);
});
store.commit('auth/setRefreshingCall', refreshingCall);
return refreshingCall;
}
This would always return either already created request as a Promise or create the new one and save it for the other calls. Now your interceptor would look similar to the following one.
Axios.interceptors.response.use(response => response, error => {
const status = error.response ? error.response.status : null
if (status === 401) {
return refreshToken(store).then(_ => {
error.config.headers['Authorization'] = 'Bearer ' + store.state.auth.token;
error.config.baseURL = undefined;
return Axios.request(error.config);
});
}
return Promise.reject(error);
});
This will allow you to execute all the pending requests once again. But all at once, without any querying.
If you want the pending requests to be executed in the order they were actually called, you need to pass the callback as a second parameter to the refreshToken() function, like so.
function refreshToken(store, cb) {
if (store.state.auth.isRefreshing) {
const chained = store.state.auth.refreshingCall.then(cb);
store.commit('auth/setRefreshingCall', chained);
return chained;
}
store.commit('auth/setRefreshingState', true);
const refreshingCall = Axios.get('get token').then(({ data: { token } }) => {
store.commit('auth/setToken', token)
store.commit('auth/setRefreshingState', false);
store.commit('auth/setRefreshingCall', undefined);
return Promise.resolve(token);
}).then(cb);
store.commit('auth/setRefreshingCall', refreshingCall);
return refreshingCall;
}
And the interceptor:
Axios.interceptors.response.use(response => response, error => {
const status = error.response ? error.response.status : null
if (status === 401) {
return refreshToken(store, _ => {
error.config.headers['Authorization'] = 'Bearer ' + store.state.auth.token;
error.config.baseURL = undefined;
return Axios.request(error.config);
});
}
return Promise.reject(error);
});
I haven't tested the second example, but it should work or at least give you an idea.
Working demo of first example - because of the mock requests and demo version of service used for them, it will not work after some time, still, the code is there.
Source: Interceptors - how to prevent intercepted messages to resolve as an error

Why not try something like this ?
Here I use AXIOS interceptors in both directions. For the outgoing direction I set the Authorization header. For the incoming direction - if there is an error, I return a promise (and AXIOS will try to resolve it). The promise checks what the error was - if it was 401 and we see it for the first time (i.e. we are not inside the retry) then I try to refresh the token. Otherwise I throw the original error.
In my case refreshToken() uses AWS Cognito but you can use whatever suits you most. Here I have 2 callbacks for refreshToken():
when the token is successfully refreshed, I retry the AXIOS request using an updated config - including the new fresh token and setting a retry flag so that we do not enter an endless cycle if the API repeatedly responds with 401 errors. We need to pass the resolve and reject arguments to AXIOS or otherwise our fresh new promise will be never resolved/rejected.
if the token could not be refreshed for any reason - we reject the promise. We can not simply throw an error because there might be try/catch block around the callback inside AWS Cognito
Vue.prototype.$axios = axios.create(
{
headers:
{
'Content-Type': 'application/json',
},
baseURL: process.env.API_URL
}
);
Vue.prototype.$axios.interceptors.request.use(
config =>
{
events.$emit('show_spin');
let token = getTokenID();
if(token && token.length) config.headers['Authorization'] = token;
return config;
},
error =>
{
events.$emit('hide_spin');
if (error.status === 401) VueRouter.push('/login'); // probably not needed
else throw error;
}
);
Vue.prototype.$axios.interceptors.response.use(
response =>
{
events.$emit('hide_spin');
return response;
},
error =>
{
events.$emit('hide_spin');
return new Promise(function(resolve,reject)
{
if (error.config && error.response && error.response.status === 401 && !error.config.__isRetry)
{
myVue.refreshToken(function()
{
error.config.__isRetry = true;
error.config.headers['Authorization'] = getTokenID();
myVue.$axios(error.config).then(resolve,reject);
},function(flag) // true = invalid session, false = something else
{
if(process.env.NODE_ENV === 'development') console.log('Could not refresh token');
if(getUserID()) myVue.showFailed('Could not refresh the Authorization Token');
reject(flag);
});
}
else throw error;
});
}
);

This could be done with a single interceptor:
let _refreshToken = '';
let _authorizing: Promise<void> | null = null;
const HEADER_NAME = 'Authorization';
axios.interceptors.response.use(undefined, async (error: AxiosError) => {
if(error.response?.status !== 401) {
return Promise.reject(error);
}
// create pending authorization
_authorizing ??= (_refreshToken ? refresh : authorize)()
.finally(() => _authorizing = null)
.catch(error => Promise.reject(error));
const originalRequestConfig = error.config;
delete originalRequestConfig.headers[HEADER_NAME]; // use from defaults
// delay original requests until authorization has been completed
return _authorizing.then(() => axios.request(originalRequestConfig));
});
The rest is an application specific code:
Login to api
Save/load auth data to/from storage
Refresh token
Check out the complete example.