I`m having some problems trying to listen to state changes in this application. Basically I was expecting a useEffect hook to be fired after some state changed, but nothing at all is happening.
This is what I got
index.jsx
// this is a simplification.
// I actually have a react-router-dom's Router wrapping everything
// and App is a Switch with multiple Route components
ReactDOM.render(
<Provider>
<App>
</Provider>
, document.getElementById('root'));
useSession.jsx
export const useSession = () => {
const [session, setSession] = useState(null)
const login = useCallback(() => {
// do something
setSession(newSession)
})
return {
session,
setSession,
login
}
}
Provider.jsx
const { session } = useSession();
useEffect(() => {
console.log('Print this')
}, [session])
// more code ...
App.jsx
export function Login() {
const { login } = useSession();
return <button type="button" onClick={() => { login() }}>Login</button>
}
Well I have this Parent component Provider watching the session state, but when it is updated the useEffect of the provider is never called.
The useEffect is fired only if the setSession is called in the same hook/method. For example, if I import the setSession in the Provider and use it there, the useEffect will be fired; Or if I add a useEffect in the useSession method, it is gonna be fired when login updates the state.
The callback of useEffect is called but only once, when the component is mounted, but not when the state is changed.
How can I achieve this behavior? Having the Provider's useEffect fired whenever session is updated?
Thanks in advance!
I think this is just a bit of misunderstanding of how custom hooks work.Every instance of the component has its own state. Let me just show a simple example illustrating this.
function App () {
return (
<div>
<ComponentA/>
<ComponentB/>
<ComponentC/>
<ComponentD/>
</div>
)
}
function useCounter() {
const [counter, setCounter] = React.useState(0);
function increment() {
setCounter(counter+1)
}
return {
increment, counter, setCounter
}
}
function ComponentA() {
const { counter, increment }= useCounter()
return (
<div>
<button onClick={()=>increment()}>Button A</button>
ComponentA Counter: {counter}
</div>
)
}
function ComponentB() {
const { counter, increment }= useCounter()
return (
<div>
<button onClick={()=>increment()}>Button B</button>
ComponentB Counter: {counter}
</div>
)
}
function ComponentC() {
const { counter }= useCounter();
return (
<div>
ComponentC Counter: {counter}
</div>
)
}
function ComponentD() {
const [toggle, setToggle] = React.UseState(false);
const { counter }= useCounter();
React.useEffect(() => {
setInterval(()=>{
setToggle(prev => !prev);
}, 1000)
})
return (
<div>
ComponentD Counter: {counter}
</div>
)
}
From the above code if you can see that incrementing count by clicking Button Awill not affect the count instance of ComponentB.This is because every instance of the component has its own state. You can also see that clicking either buttons won't trigger ComponentC to rerender since they don't share the same instance. Even if i trigger rerender every one second like in Component D thus invoking useCounter the counter in ComponentD remains 0.
Solution
However there are multiple ways of making components share/listen to same state changes
You can shift all your state i.e [session state] to the Provider component and make it visible to other components by passing it via props.
You can move state to a global container Redux or simply use Context Api + UseReducer Hook here is an example
But since you are dealing with auth and session management, I suggest you persist the session state in local storage or session storage, and retrieve it whenever you need it. Hope that helped
Related
React throw an error when we try to update the state on an unmounted component.So When I test react component for that I am getting errors on the first render only.
I made a component that enable child component based on click. And child component have button which updates state after some settimeout which throw react warning
Warning: Can't perform a React state update on an unmounted component. This is a no-op, but it indicates a memory leak in your application. To fix, cancel all subscriptions and asynchronous tasks in a useEffect cleanup function.
Which is perfectly valid. But to overcome this I am passing enable props from the parent component based on that there is a condition just before setTimeout in the child component. So why does it throw an error the first time only?
To reproduce
Click on the child component button which is false and click on parent component button enable which unmount the child component.
**My question is why react throw an error on the first time only ? And why it is working fine on second time **
Parent component
import { useState } from "react";
import "./styles.css";
import { Test } from "./Test";
export default function App() {
const [state, setstate] = useState(true);
const changeState = () => {
setstate(!state);
};
return (
<div className="App">
<button onClick={changeState}>enable </button>
{state && <Test enable={state} />}
</div>
);
}
Child Component
import React, { useState } from "react";
export const Test = (props) => {
const [state, setstate] = useState(false);
const fetchData = () => {
setstate(!state);
if (props.enable) {
setTimeout(() => {
setstate(false);
}, 1000);
}
};
return (
<>
<button onClick={fetchData}> {`${state}`}</button>
</>
);
};
Codesandbox link to test
Nice track, Just you are missing a minor point, when you write a state thats needed some time to execute and the same time we can visit the flow again and again base on any action, then we need to clear old subscription before go to new one...
For example, in your code here, you update state flow, but the state flow is register a new subscription every time we visit a component with valid props and click on button, so that, prev execution may still work when you trigger new event, so simply, what we need to do unmounted old subscription and we can do that by this for your case:
import React, { useState, useEffect } from "react";
export const Test = (props) => {
const [state, setstate] = useState(false);
useEffect(() => {
if (props.enable) {
const timer = setTimeout(() => {
setstate(false);
}, 1000);
return () => clearTimeout(timer);
}
}, [state, props.enable]);
const fetchData = () => {
setstate((prev) => !prev);
};
return (
<>
<button onClick={fetchData}> {`${state}`}</button>
</>
);
};
Look at code above, simply we add code need to cleanup in effect which its look to my state and prop, now when I click on button, the effect will trigger, if we do that again, the clearTime will work for prev subscription and then add new one and so on...
Notes:
In your case we can remove function and use setState direct on your button.
Prefer to use useCallBack in your function like const fetchData = useCAllback...
You can use setstate((prev) => !prev); its will be work as snapshot, and its usefull when you depends on old value..but may it not needed in some cases too, but just to know about this feature.
Update 1:
What is Subscription:
You can say the subscription represents a disposable resource, such as the execution of an Observable. A Subscription has one important method, unsubscribe, that takes no argument and just disposes the resource held by the subscription, in another word, you can say yes, any async task or any job will be invoke to react life-cycle state and its needed to observe changes, then you talk about subscribe, like API or time out or time interval and so on, any of these action thats need to clear prev subscribe (stop observer - unsubscribe) to prevent any memory leek and clear memory to keep state flow safe and prevent unneeded reredner.
enter image description here
Please look at the time printed on the console.
setInterval() looks like being called twice in on interval.
I attached my code below. I'd really appreciate it if you could give me a clue to the solution.
import React, {useState} from 'react';
import AppRouter from './Router';
import {authService} from '../fbase';
function App() {
console.log('App()');
const [isLoggedIn, setIsLoggedIn] = useState(authService.currentUser);
console.log(authService.currentUser);
setInterval(() => {
console.log(Date().toLocaleString());
console.log('In App.js > App()');
console.log(authService.currentUser);
}, 5000);
return <AppRouter isLoggedIn={isLoggedIn}></AppRouter>;
}
export default App;
Every time a state/prop changes your component will re-render. This means that everything that is not wrapped in a hook of some kind will also re-run. I'm not sure why this happens to you, maybe authService.currentUser returns two different values, an initial (probably empty) one when mounting the component and the correct one after it does some calculations (maybe you request the user from the back-end and it takes a while to get back the response -- some more code would be helpful here).
When the actual (correct) value will be returned from the authService to your function component it will re-render thus running setInterval again.
In order to make sure this never happens it's best to wrap our functionalities in a hook. If you want to run the setInterval just ONCE (when mounting the component) we can wrap it in an useEffect with an empty dependency array:
useEffect(() => {
setInterval(() => {
...
}, 5000)
), []}
This means the hook will only run when your component first mounts.
If you need to run it based on some prop change (like when isLoggedIn changes from false to true or viceversa) you can add that to the dependency array and your interval will run every time isLoggedIn state changes:
useEffect(() => {
setInterval(() => {
...
}, 5000)
}, [ isLoggedIn ])
If you only need to run that when isLoggedIn changes from false to true you can also add an if condition in your useEffect like this:
useEffect(() => {
if (isLoggedIn) {
setInterval(() => {
...
}, 5000)
}
}, [ isLoggedIn ])
More than that, as Jose Antonio Castro Castro mentioned, in all of the above cases you need to use a cleanup function in order to stop the interval from running indefinitely when your component unmounts (because it has no way of knowing to stop by itself). This is achieved by returning a function from your effect:
useEffect(() => {
const interval = setInterval(() => {
...
}, 5000)
return () => clearInterval(interval);
), []}
Don't forget that every time your component feels like re-rendering, all of your constants and functions that are called directly at the root of your component will be re-declared / re-run again.
The useEffect, useCallback, useMemo hooks help us with exactly that, but in different ways. Choose and use them wisely!
As in the comments, you need to call setInterval when you mount the component, but you need to stop the timer when it is unmounted.
const App = (props) => {
const [count, setCount] = React.useState(0)
React.useEffect(function appRunTimer() {
// Creates a new timer when mount the component.
const timer = setInterval(() => {
console.log(Date().toLocaleString())
console.log('In App.js > App()')
}, 5000)
// Stops the old timer when umount the component.
return function stopTimer() {
clearInterval(timer)
}
}, [])
console.log('DRAW')
return (
<button onClick={() => {setCount(count + 1)}}>
Click to update component's state: You click me {count} time(s)
</button>
);
};
ReactDOM.render(<App />, document.getElementById("root"));
<script crossorigin src="https://unpkg.com/react#17/umd/react.production.min.js"></script>
<script crossorigin src="https://unpkg.com/react-dom#17/umd/react-dom.production.min.js"></script>
<div id="root"></div>
This may seem like a weird question, but I do not really see many use cases for useEffect in React (I am currently working on a several thousand-lines React codebase, and never used it once), and I think that there may be something I do not fully grasp.
If you are writing a functional component, what difference does it make to put your "effect" code in a useEffect hook vs. simply executing it in the body of the functional component (which is also executed on every render) ?
A typical use case would be fetching data when mounting a component : I see two approaches to this, one with useEffect and one without :
// without useEffect
const MyComponent = () => {
[data, setData] = useState();
if (!data) fetchDataFromAPI().then(res => setData(res));
return(
{data ? <div>{data}</div> : <div>Loading...</div>}
)
}
// with useEffect
const MyComponent = () => {
[data, setData] = useState();
useEffect(() => {
fetchDataFromAPI().then(res => setData(res))
}, []);
return(
{data ? <div>{data}</div> : <div>Loading...</div>}
)
}
Is there an advantage (performance-wise or other) to useEffect in such usecases ?
I. Cleanup
What if your component gets destroyed before the fetch is completed? You get an error.
useEffect gives you an easy way to cleanup in handler's return value.
II. Reactions to prop change.
What if you have a userId passed in a props that you use to fetch data. Without useEffect you'll have to duplicate userId in the state to be able to tell if it changed so that you can fetch the new data.
The thing is, useEffect is not executed on every render.
To see this more clearly, let's suppose that your component MyComponent is being rendered by a parent component (let's call it ParentComponent) and it receives a prop from that parent component that can change from a user action.
ParentComponent
const ParentComponent = () => {
const [ counter, setCounter ] = useState(0);
const onButtonClicked = () => setCounter(counter + 1);
return (
<>
<button onClick={onButtonClicked}>Click me!</button>
<MyComponent counter={counter} />
</>
);
}
And your MyComponent (slightly modified to read and use counter prop):
const MyComponent = ({ counter }) => {
[data, setData] = useState();
useEffect(() => {
fetchDataFromAPI().then(res => setData(res))
}, []);
return(
<div>
<div>{counter}</div>
{data ? <div>{data}</div> : <div>Loading...</div>}
</div>
)
}
Now, when the component MyComponent is mounted for the first time, the fetch operation will be performed. If later the user clicks on the button and the counter is increased, the useEffect will not be executed (but the MyComponent function will be called in order to update due to counter having changed)!
If you don't use useEffect, when the user clicks on the button, the fetch operation will be executed again, since the counter prop has changed and the render method of MyComponent is executed.
useEffect is handling the side effect of the problem. useEffect is the combination of componentDidMount and componentDidUpdate. every initial render and whenever props updated it will be executed.
For an exmaple:
useEffect(() => {
fetchDataFromAPI().then(res => setData(res))
}, []);
Another example:
let's assume you have multiple state variables, the component will re-render for every state values change. But We may need to run useEffect in a specific scenario, rather than executing it for each state change.
function SimpleUseEffect() {
let [userCount, setUserCount] = useState(0);
let [simpleCount, setSimpleCount] = useState(0);
useEffect(() => {
alert("Component User Count Updated...");
}, [userCount]);
useEffect(() => {
alert("Component Simple Count Updated");
}, [simpleCount]);
return (
<div>
<b>User Count: {userCount}</b>
<b>Simple Count: {simpleCount}</b>
<input type="button" onClick={() => setUserCount(userCount + 1}} value="Add Employee" />
<input type="button" onClick={() => setSimpleCount(simpleCount + 1}} value="Update Simple Count" />
</div>
)
}
In the above code whenever your props request changed, fetchDataFromAPI executes and updated the response data. If you don't use useEffect, You need to automatically handle all type of side effects.
Making asynchronous API calls for data
Setting a subscription to an observable
Manually updating the DOM element
Updating global variables from inside a function
for more details see this blog https://medium.com/better-programming/https-medium-com-mayank-gupta-6-88-react-useeffect-hooks-in-action-2da971cfe83f
How do I change the useState without re-rendering it but just its components? Why I need is because I have some logic that changes the useState in Comp1. If I would re-render Comp1 I would have to recalculate its value. But if the change happens I still would like to re-render its components.
Edit: bigger code snippet.
function Comp1() {
const [user, setUser] = useState({});
firebase.auth().onAuthStateChanged(function (_user) {
if (_user) {
// User is signed in.
setUser(_user);
} else {
setUser({ exists: false });
}
});
return (
<div>
<UserProvider.Provider value={{user, setUser}}>
<Comp2 />
<Comp3 />
</UserProvider.Provider>
</div>
);
}
function Comp2(props) {
const { user, setUser } = useContext(UserProvider);
return (
<div>
{user.exists}
</div>
)
}
function Comp3(props) {
const { user, setUser } = useContext(UserProvider);
return (
<div>
{user.exists}
</div>
)
}
//User Provider
import React from 'react';
const UserProvider = React.createContext();
export default UserProvider;
I took a shot at answering your question. Basically, you want to be able to calculate a value once and have it updated only when the content changes. You can do this with useEffect. The first parameter for useEffect is a function you want to happen on mount/update. It should return a function to run when your function is unmounted (if any). The second argument are the things that determine if useEffect gets ran. I put it to run when user changes value. Hopefully this is enough to get you started down the path of something. You can read more about useEffect in the docs.
function Comp2(props) {
const { user, setUser } = useContext(UserProvider);
const { state, setState } = useState({ value: '' });
useEffect(() => {
console.log(user);
// perform expensive operation
setValue({ value: 'My expensive operation is now stored' });
return () => {
// Do you have anything that you would put in componentWillUnmount()?
// Put that here
};
}, [user]);
console.log(state.value);
return (
<div>
{user.exists}
</div>
)
}
My suggestion is to ditch the useContext hooks as they seem to cause re-renders on components they're attached to.
I was experimenting with the new Hook feature in React. Considering I have the following two components (using React Hooks) -
const HookComponent = () => {
const [username, setUsername] = useState('Abrar');
const [count, setState] = useState();
const handleChange = (e) => {
setUsername(e.target.value);
}
return (
<div>
<input name="userName" value={username} onChange={handleChange}/>
<p>{username}</p>
<p>From HookComponent: {count}</p>
</div>
)
}
const HookComponent2 = () => {
const [count, setCount] = useState(999);
return (
<div>
<p>You clicked {count} times</p>
<button onClick={() => setCount(count + 1)}>
Click me
</button>
</div>
);
}
Hooks claim to solve the problem of sharing stateful logic between components but I found that the states between HookComponent and HookComponent2 are not sharable. For example the change of count in HookComponent2 does not render a change in the HookComponent.
Is it possible to share states between components using the useState() hook?
If you are referring to component state, then hooks will not help you share it between components. Component state is local to the component. If your state lives in context, then useContext hook would be helpful.
Fundamentally, I think you misunderstood the line "sharing stateful logic between components". Stateful logic is different from state. Stateful logic is stuff that you do that modifies state. For e.g., a component subscribing to a store in componentDidMount() and unsubscribing in componentWillUnmount(). This subscribing/unsubscribing behavior can be implemented in a hook and components which need this behavior can just use the hook.
If you want to share state between components, there are various ways to do so, each with its own merits:
1. Lift State Up
Lift state up to a common ancestor component of the two components.
function Ancestor() {
const [count, setCount] = useState(999);
return <>
<DescendantA count={count} onCountChange={setCount} />
<DescendantB count={count} onCountChange={setCount} />
</>;
}
This state sharing approach is not fundamentally different from the traditional way of using state, hooks just give us a different way to declare component state.
2. Context
If the descendants are too deep down in the component hierarchy and you don't want to pass the state down too many layers, you could use the Context API.
There's a useContext hook which you can leverage on within the child components.
3. External State Management Solution
State management libraries like Redux or Mobx. Your state will then live in a store outside of React and components can connect/subscribe to the store to receive updates.
It is possible without any external state management library. Just use a simple observable implementation:
function makeObservable(target) {
let listeners = []; // initial listeners can be passed an an argument aswell
let value = target;
function get() {
return value;
}
function set(newValue) {
if (value === newValue) return;
value = newValue;
listeners.forEach((l) => l(value));
}
function subscribe(listenerFunc) {
listeners.push(listenerFunc);
return () => unsubscribe(listenerFunc); // will be used inside React.useEffect
}
function unsubscribe(listenerFunc) {
listeners = listeners.filter((l) => l !== listenerFunc);
}
return {
get,
set,
subscribe,
};
}
And then create a store and hook it to react by using subscribe in useEffect:
const userStore = makeObservable({ name: "user", count: 0 });
const useUser = () => {
const [user, setUser] = React.useState(userStore.get());
React.useEffect(() => {
return userStore.subscribe(setUser);
}, []);
const actions = React.useMemo(() => {
return {
setName: (name) => userStore.set({ ...user, name }),
incrementCount: () => userStore.set({ ...user, count: user.count + 1 }),
decrementCount: () => userStore.set({ ...user, count: user.count - 1 }),
}
}, [user])
return {
state: user,
actions
}
}
And that should work. No need for React.Context or lifting state up
This is possible using the useBetween hook.
See in codesandbox
import React, { useState } from 'react';
import { useBetween } from 'use-between';
const useShareableState = () => {
const [username, setUsername] = useState('Abrar');
const [count, setCount] = useState(0);
return {
username,
setUsername,
count,
setCount
}
}
const HookComponent = () => {
const { username, setUsername, count } = useBetween(useShareableState);
const handleChange = (e) => {
setUsername(e.target.value);
}
return (
<div>
<input name="userName" value={username} onChange={handleChange}/>
<p>{username}</p>
<p>From HookComponent: {count}</p>
</div>
)
}
const HookComponent2 = () => {
const { count, setCount } = useBetween(useShareableState);
return (
<div>
<p>You clicked {count} times</p>
<button onClick={() => setCount(count + 1)}>
Click me
</button>
</div>
);
}
We move React hooks stateful logic from HookComponent to useShareableState.
We call useShareableState using useBetween in each component.
useBetween is a way to call any hook. But so that the state will not be stored in the React component.
For the same hook, the result of the call will be the same. So we can call one hook in different components and work together on one state. When updating the shared state, each component using it will be updated too.
Disclaimer: I'm the author of the use-between package.
the doc states:
We import the useState Hook from React. It lets us keep local state in a function component.
it is not mentioned that the state could be shared across components, useState hook just give you a quicker way to declare a state field and its correspondent setter in one single instruction.
I've created hooksy that allows you to do exactly this - https://github.com/pie6k/hooksy
import { createStore } from 'hooksy';
interface UserData {
username: string;
}
const defaultUser: UserData = { username: 'Foo' };
export const [useUserStore] = createStore(defaultUser); // we've created store with initial value.
// useUserStore has the same signature like react useState hook, but the state will be shared across all components using it
And later in any component
import React from 'react';
import { useUserStore } from './userStore';
export function UserInfo() {
const [user, setUser] = useUserStore(); // use it the same way like useState, but have state shared across any component using it (eg. if any of them will call setUser - all other components using it will get re-rendered with new state)
function login() {
setUser({ username: 'Foo' })
}
return (
<div>
{!user && <strong>You're logged out<button onPress={login}>Login</button></strong>}
{user && <strong>Logged as <strong>{user.username}</strong></strong>}
</div>
);
}
With hooks its not directly possible.
I recommend you to take a look at react-easy-state.
https://github.com/solkimicreb/react-easy-state
I use it in big Apps and it works like a charm.
I'm going to hell for this:
// src/hooks/useMessagePipe.ts
import { useReducer } from 'react'
let message = undefined
export default function useMessagePipe() {
const triggerRender = useReducer((bool) => !bool, true)[1]
function update(term: string) {
message = term.length > 0 ? term : undefined
triggerRender()
}
return {message: message, sendMessage: update}
}
Full explanation over at: https://stackoverflow.com/a/72917627/1246547
Yes, this is the dirtiest and most concise way i could come up with for solving that specific use case. And yes, for a clean way, you probably want to learn how to useContext, or alternatively take a look at react-easy-state or useBetween for low-footprint solutions, and flux or redux for the real thing.
You will still need to lift your state up to an ancestor component of HookComponent1 and HookComponent2. That's how you share state before and the latest hook api doesnt change anything about it.