So here's my scenario: I have a client page, where any one can fill and submit a form. the form data is stored in a database. There is a separate admin pc which is on an admin page, where every new form entry is displayed. How to update the front end of the admin everytime a new form is submitted, without refreshing/re hitting the API?
I am using React with express and MongoDB.
You can use TanStack Query (also called react query) ,
it's useQuery (a data fetching method) has a build-in property called isFetching which allow automatic fetching in a specific interval you want, like :
const { data,isLoading,isFetching } = useQuery(
['random-data'],
async () => {
const { data } = await axios.get(
'https://random-data-api.com/api/v1/random_data'
);
return data;
},
{
// refetch data every sec.
refetchInterval: 1000,
}
);
you can check more here
I have a node server that performs CRUD operations on data stored in a MongoDB Atlas database. My front-end is made using react where i am using redux for state management. Before I had the backend setup, I was initializing the default state of the redux store by calling a function i made which just returns JSON data. Now I want to make a get request to the server via axios to retrieve that same JSON data which is now on the Mongo database.
I know that I should be making axios get calls in componentDidMount lifecycle hook but my store.js is not a class but i'm not sure how. I am however able to just do axios.get(URL) but it returns an object in the form of [[PromiseStatus]]:"resolved", [[PromiseValue]]:{the data i want}. I read that these are not accessible. Im wondering if it is because I am not making the axios call in the right place or in the right time in the lifecycles.
import { createStore } from "redux";
//import { syncHistoryWithStore } from "react-router-redux";
//import { browserHistory } from "react-router-dom";
import axios from "axios";
//import the root reducer.
import rootReducer from "../reducers/rootReducer";
//this is just getting JSON from a file
import { getAnnotations } from "../services/fakeEntry";
//create an object for default data
const defaultState = {
//This is how i was creating the default state before.
// metadata: getAnnotations()
//this is what id like to do.But this needs to be in a lifecycle hook?
metadata: axios
.get("http://localhost:5100/data/")
.then(response => {
return response;
})
.catch(function(error) {
console.log(error);
})
};
const store = createStore(rootReducer, defaultState);
export default store;
The code above is the redux store. I have tested the endpoint using postman and it returns the JSON data. When i read this redux state using mapStateToProps in another component i get returned a Promise object.
I see two mistakes in your approach.
Redux is built from principles of functional programming and based on pure functions (without side effects, like API calls). So default state should some default empty object like below
const defaultState = {
metadata: {} // It should be empty during store init
isDataInitialized: false // You can add additional property to denote, that data is not fetched for the first time
}
axios returns Promise (as you already discovered). So take data from Promise, you should either user .then and set data in callback, or use async\await
Here is sample using async\await
// Now it is function, not object
const getInitalData = () => async dispatch => {
try {
let metadata = await axios
.get("http://localhost:5100/data/");
// You're dispatching not only the metadata, but also setting isDataInitialized to true, to denote, that data has been loaded
dispatch ({ type: 'DATA_INITIALIZED', metadata, isDataInitialized: true });
}
catch {
console.log(error);
}
}
Essentially getInitalData is action creator, which will dispatch action DATA_LOADED to store.
And you should create store with middleware (like thunk), to be able to dispatch actions which are functions.
const store = createStore(rootReducer, applyMiddleware(
thunkMiddleware
))
defaultState should go to reducer directly, like below
rootReducer (state = defaultState, action) {
// ...
Then, in some root component of your app, you call getInitalData to load data from server to store.
Here is simple sample you can use for better understanding
I have a node backend with firebase auth that connects to an angular frontend. I have two component that is the navbar and the register form, when I register I call a backend function to register in firebase and sent back the firebase.auth().currentUser, how should my angular frontend navbar detects the arrival of such user and updates itself accordingly, without me refresh the page?
I assume this is how your components are structured:
// In app.component.html
<app-navbar></app-navbar>
<router-outlet></router-outlet> // For rest of the pages.
Here, there are 2 ways (I'll not talk about including ngModel) by which we can pass data to navbar for updating the status/data of navbar.
1. Using Input/Output decorators.
// Your navbar.component.ts
// I'm assuming you have set up model for User. If no, then change the type to **any**.
#Input() currentUser: IUser;
// Your navbar.component.html
<p *ngIf="currentUser"> {{currentUser | json}} </p> // Render this if currentUser exists. By default, it is undefined.
Now, in your App component:
//In your app.component.ts
User: any | IUser;
public authenticateUser() {
this.someServiceToAuthenticateUser.subscribe(
res => this.User = res,
error => console.error(error)
);
}
// In your app.component.html
<app-navbar [currentUser]="User"></app-navbar>
<router-outlet></router-outlet>
Using a common service.
You can create the common service which stores the authenticated user in it. From your App component, you can set the user on the success of authenticating the response and from other components, you can fetch the authenticated user.
export class UserService {
private currentUser: IUser | any;
setCurrentUser(userToSet: any) {
this.currentUser = userToSet;
}
getCurrentUser() {
return this.currentUser;
}
Now, in your App component, if the request for authenticating the use is a success, then set the currentUser of UserService:
//In your app.component.ts
User: any | IUser;
public authenticateUser() {
this.someServiceToAuthenticateUser.subscribe(
res => this.UserService.setCurrentUser(res),
error => console.error(error)
);
}
Now, in your navbar component, get the current user from UserService.
// In navbar.component.ts
currentUser: any;
constructor(private userServicce: UserService) {
getuserFromservice();
}
public getuserFromservice() {
setInterval(() => {
curretnUser = this.userService.getCurrentUser()
}, 3000);
Important: In this approach, notice in navbar component, I have set the current user in setInterval. This is because your getuserFromservice() will run only once (when it is created/rendered for the first time) and at this time, userService will have no currentUser. So navbar will never get the currenUser.
If you want to replace the setInterval approach (I highly encourage to replace it), then use Subjects/BehaviourSubject/ReplaySubject. I did not include them here because Rxjs is a huge topic in itself and including it would be too much to understand here.
Input & Output operator is good but It can't provide flexibility of sharing data like observable
Here You need to use Subject Observable to share data among the app. It's very easy and useful thing. You can send signal to all the lisner when user is registered.
What you need to do
1) Create one service file to share data
- service have subject observable. Using that you can subscribe the channel for user data
2) In the your header component listener that service and set the listener coming data to header user data
3) From your register, Profile update,or anywhere else user data was update, just past that data to subject observable it will automatically update user in entire app. follow below example to achieve this
You can find the working demo in below link
https://jasonwatmore.com/post/2019/02/07/angular-7-communicating-between-components-with-observable-subject
Let's say I have a user's account information stored in localStorage (client side). I need my Next.JS app to render the webpage's navbar based on what's stored in localStorage (login or logout button). How can I first obtain the value from the client and then render the page? Or perhaps that isn't even what Next.JS is meant to do?
You can do something like this:
Use a variable in the state to prevent the page from being rendered
Use componentDidMount to load data from localStorage
When data is loaded, setState to allow component to be rendered.
It's a react issue, not a next.js issue.
You could use Conditional rendering for step 1.
Also read up on state here, and lastly componentDidMount.
Update:
Nowadays, I would opt for a React hooks implementation instead, but the idea still stands. useEffect can largely accomplish this with some nuances in some situations.
I also realize that there are some possible caveats with NextJS and SSR logic specifically, so this response may not be sufficient. In such cases, I would also look into some other responses below.
As mentioned at https://stackoverflow.com/a/54819843/895245 I haven't been able to truly get localStorage before the first render, only show a fallback page until that happens.
The fundamental issue is that Next.js maps one URL to one pre-render. And React hydration requires the initial server HTML to match the JavaScript structure:
React expects that the rendered content is identical between the server and the client. It can patch up differences in text content, but you should treat mismatches as bugs and fix them. In development mode, React warns about mismatches during hydration. There are no guarantees that attribute differences will be patched up in case of mismatches. This is important for performance reasons because in most apps, mismatches are rare, and so validating all markup would be prohibitively expensive.
That quote is not very clear if text-only changes work or not but the minimal test below shows that it raises a warning in that case, so you don't want to use it.
Therefore the only sure-fire way it to use useEffect to update the page afterwards.
However, when I've tested, the correct render with localStorage shows up so quickly that the intermediate one it is not noticeable at all, I'm not sure it even happens. The only problem is if you make different API calls on each case, see section "Differentiate between "not logged in" and "haven't decided yet" to avoid doing extra API calls" below for an example of that.
What I would like to do is to give a slightly more concrete idea about what was mentioned in that answer.
SWR example
Here is a complete runnable example where the navbar shows login status: https://github.com/cirosantilli/node-express-sequelize-nextjs-realworld-example-app That repository is a fork of this one, both of which are Next.js implementations of the awesome realworld project.
The fallback in that case is just the signed out view of the blog pages, which already contain the key information users are likely to want to see, and can be cached e.g. with ISR.
That demo uses SWR to make the code slightly simpler. The key parts are:
navbar code
login code
The key parts of the code there are:
navbar:
import useSWR from "swr";
const Navbar = () => {
const { data: currentUser } = useSWR("user", key => {
const value = localStorage.getItem(key);
return !!value ? JSON.parse(value) : undefined;
});
login:
import { mutate } from "swr";
const LoginForm = () => {
const handleSubmit = async (e) => {
// Get `user` data structure from API.
mutate("user", data?.user);
We see that when the user logins, we call mutate on the "user" global identifier.
This redraws all components that contain that hook, which includes the navbar, as it setup the hook with the useSWR call.
This way, login first redraws the navbar, and then redirects you to home, so that the home page will have the redrawn navbar immediately. Without mutate, only the page body would redraw, not the navbar.
With this setup:
if you put a console.log(currentUser) just below useSWR, you see that it gets called twice.
So what happens is that it first returns immediately with a cached value (undefined) and the first render starts.
It then starts an async call to the cache, and when that returns, the hook triggers a re-render of the component, and the print happens again with the current user value.
This only happens on initial hydration during refresh/first hit. During internal page changes, there is just a single render.
All of this happens so fast that I can't see the page draw without hte local storage at all, not even with the Chromium debugger timeline frame inspection.
if we add a 2 second delay to the localStorage getter however:
const { data: currentUser } = useSWR("user", async (key) => {
await new Promise(resolve => setTimeout(resolve, 2000))
const value = localStorage.getItem(key);
return !!value ? JSON.parse(value) : undefined;
});
we do observe an intermediate page state with the user logged out, so it could in theory happen.
How it would look like without SWR
Of course, we wouldn't need to use SWR to achieve this.
The SWR documentation gives us the rationale of how thing would look like without SWR https://swr.vercel.app/getting-started to motivate their library.
You would either need to move the state up to a common parent of the login form + navbar, or you could use Context.
function Page () {
const [user, setUser] = useState(null)
// fetch data
useEffect(() => {
const value = localStorage.getItem(key);
const user = !!value ? JSON.parse(value) : undefined;
setUser(user)
}, [])
// global loading state
if (!user) return <Spinner/>
return <div>
<Navbar user={user} />
<Content user={user} />
</div>
}
// child components
function Navbar ({ user }) {
return <div>
...
<Avatar user={user} />
</div>
}
function Content ({ user }) {
return <h1>Welcome back, {user.name}</h1>
}
function Avatar ({ user }) {
return <img src={user.avatar} alt={user.name} />
}
As mentioned at What is difference between lifecycle method and useEffect hook? useEffect is the hook analogue to componentDidMount.
Checking typeof localStorage === 'undefined' leads to a warning
React doesn't like that and warns with something like:
Expected server HTML to contain a matching"
as it notices the difference between hydrated and non-hydrated pages: React 16: Warning: Expected server HTML to contain a matching <div> in <body>
Tested on Next.js 10.2.2.
Minimal reproducible example
Just to play with and see exactly what happens:
pages/index.js
import Link from 'next/link'
import React from 'react'
export default function IndexPage() {
console.error('IndexPage');
let [n, setN] = React.useState(0)
if (typeof localStorage === 'undefined') {
n = '0'
} else {
n = parseInt(localStorage.getItem('n') || '0', 10)
}
return <>
<Link href="/notindex">notindex</Link>
<div
onClick={() => {
localStorage.setItem('n', n + 1)
setN(n + 1)
}}
>increment</div>
<div
onClick={() => {
localStorage.removeItem('n')
setN(0)
}}
>reset</div>
<div>{n}</div>
</>
}
pages/notindex.js
import Link from 'next/link'
export default function NotIndexPage() {
return <Link href="/">index</Link>
}
package.json
{
"name": "test",
"version": "1.0.0",
"scripts": {
"dev": "next",
"build": "next build",
"start": "next start"
},
"dependencies": {
"next": "12.0.7",
"react": "17.0.2",
"react-dom": "17.0.2"
}
}
Run:
npm install
npm run dev
Now, if you:
open /
increment
refresh the page
react gives a warning because it notices that the 0 text was changed to 1:
Warning: Text content did not match. Server: "0" Client: "1"
If we click the internal links however to notindex and back, we don't see the warning. This is because hydration is only done on the initial page refresh, further changes are done in Js only.
What we have to do instead is something like this:
import Link from 'next/link'
import React from 'react'
export default function IndexPage() {
console.error('IndexPage');
let [n, setN] = React.useState(0)
React.useEffect(() => {
console.error('useEffect');
setN(parseInt(localStorage.getItem('n') || '0', 10))
}, [])
return <>
<Link href="/notindex">notindex</Link>
<div
onClick={() => {
setN(n + 1)
localStorage.setItem('n', n + 1)
}}
>increment</div>
<div
onClick={() => {
localStorage.removeItem('n')
setN(0)
}}
>reset</div>
<div>{n}</div>
</>
}
Differentiate between "not logged in" and "haven't decided yet" to avoid doing extra API calls
OK, I had another issue: I was making unnecessary API calls, because first the page thought the user was logged out, and then it thought it was logged in, and each of those needed to do different API calls.
Unlike starting to render the wrong page, this would actually have server load consequences, so it was not acceptable.
The solution I used was to differentiate between:
undefined: haven't decided
null: not logged-in
and not make any requests on undefined.
Here's a non-minimized demo:
https://github.com/cirosantilli/node-express-sequelize-nextjs-realworld-example-app/blob/2bbce5199d3a7efa19a3a58426bea25a1cd37579/front/ArticleList.tsx#L33
https://github.com/cirosantilli/node-express-sequelize-nextjs-realworld-example-app/blob/2bbce5199d3a7efa19a3a58426bea25a1cd37579/front/useLoggedInUser.ts
I'll try to minimize it later on.
Another solution: just do SSR
In general, SSR is way simpler than ISR, because you don't have to worry about this get page/ask for data/get data/update page dance from Hell.
ISR is an optimization, and you should only use if there's a proven performance benefit.
Remember that SSR in Next.js is also very data efficient, as Next.js returns only the .json from getServerSideProps on page switches, basically exactly like an API would.
You can then just do authentication from getServerSideProps with cookies, and return the correct page straightaway.
This is how I did it.
const setSession = (accessToken) => {
if (typeof window !== 'undefined')
localStorage.setItem('accessToken', accessToken);
};
const getAccessToken = () => {
if (typeof window !== 'undefined')
return localStorage.getItem('accessToken');
};
Here is where I call them to handle login and to get the access token:
const loginWithEmailAndPassword = async (email, password) => {
const { data } = await axios.post(`${apiUrl}/login`, { email, password });
const { user, accessToken } = data;
if (user) {
setSession(accessToken);
return user;
}
};
const accessToken = getAccessToken();
local storage is not available on the server, there are two options to resolve this
1: create HOC or custom hook to check if the local storage has the data (this is normal react way)
2: you can use cookies to store data on client and server side , which can be then be used getServerSideProps to extract the data and and you can then use this data to display the information accordingly on the initial render.
you can use useEffect hook and useState, so that when component loads, useEffect will fire last, extract data from localStorage and assign it to a STATE from useState.
then you can access your data from useState, states. if that makes sense.
Bottom line, useEffect allows to easily extract data from localStorage, so then you can do what you like with it.
const [userData, setUserData] = useState({});
console.log(userData);
useEffect(()=> {
setUserData(localStorage.getItem('userSession'));
}, [])
The first render which happen on server side can not have access to localStorage and throw the error. To prevent this, add an extra layer of defense with
if (typeof window !== 'undefined') {
// run logic that read/write localStorage
}
Then it should skip the logic when on server and run it when loaded on client side
I'm using Jest and React-testing-library to test a React component. I've rendered a component with a Context API Provider so the component has access to the Context. Unfortunately, I don't know how could I access it from outside the rendered component. In this case there is an isUserLogged property in the Context depending on which the component changes. But I don't know how could I change the value of this property. How could I approach this case? If mocking of the Context API required how could I do it?
In the attached code I try to access a Context using a useContext hook. The error says I can't use hooks outside of React components. And, obviously, I'm trying to access the Context outside the Context Provider so it wouldn't work anyway.
import { Provider, Context } from '../../context';
test('Star is not clickable for a non-registered user', () => {
const { getByTestId } = render(<Provider><Star /></Provider>);
const isUserLogged = useContext(Context).isUserLogged; // Error.
});
You simply have to render your Provider passing a value prop. That's how you would do it in your app.
const isUserLogged = true
render(<Provider value={{ isUserLogged }}><Star /></Provider>)
This is how I access to context in order to initialise state to be ready for a function being tested:
let authContext
const TestWrapper = ({ children }) => {
authContext = useContext(AuthContext)
return children
}
const renderer = renderHook(() => useAuth(), {
wrapper: ({ children }) => (
<AuthProvider>
<TestWrapper>{children}</TestWrapper>
</AuthProvider>
),
})
act(() => {
authContext.setUser(user)
})
// hook that uses the same context now have 'user' initialised