I have an object which value updates and i would like to know if there is a way to re-render the component when my object value is updated.
I can't create a state object because the state won't be updated whenever the object is.
Using a ref is not a good idea(i think) since it does not cause a re-render when updated.
The said object is an instance of https://docs.kuzzle.io/sdk/js/7/core-classes/observer/introduction/
The observer class doesn't seem to play well with your use case since it's just sugar syntax to manage the updates with mutable objects. The documentation already has a section for React, and I suggest following that approach instead and using the SDK directly to retrieve the document by observing it.
You can implement this hook-observer pattern
import React, { useCallback, useEffect, useState } from "react";
import kuzzle from "./services/kuzzle";
const YourComponent = () => {
const [doc, setDoc] = useState({});
const initialize = useCallback(async () => {
await kuzzle.connect();
await kuzzle.realtime.subscribe(
"index",
"collection",
{ ids: ["document-id"] },
(notification) => {
if (notification.type !== "document" && notification.event !== "write")
return;
// getDocFromNotification will have logic to retrieve the doc from response
setDoc(getDocFromNotification(notification));
}
);
}, []);
useEffect(() => {
initialize();
return () => {
// clean up
if (kuzzle.connected) kuzzle.disconnect();
};
}, []);
return <div>{JSON.stringify(doc)}</div>;
};
useSyncExternalStore, a new React library hook, is what I believe to be the best choice.
StackBlitz TypeScript example
In your case, a simple store for "non state object" is made:
function createStore(initialState) {
const callbacks = new Set();
let state = initialState;
// subscribe
const subscribe = (cb) => {
callbacks.add(cb);
return () => callbacks.delete(cb);
};
// getSnapshot
const getSnapshot = () => state;
// setState
const setState = (fn) => {
state = fn(state);
callbacks.forEach((cb) => cb());
};
return { subscribe, getSnapshot, setState };
}
const store = createStore(initialPostData);
useSyncExternalStore handles the job when the update of "non state object" is performed:
const title = React.useSyncExternalStore(
store.subscribe,
() => store.getSnapshot().title
);
In the example updatePostDataStore function get fake json data from JSONPlaceholder:
async function updatePostDataStore(store) {
const response = await fetch(`https://jsonplaceholder.typicode.com/posts/${Math.floor(Math.random()*100)+1}`)
const postData = await response.json()
store.setState((prev)=>({...prev,...postData}));
};
My answer assumes that the object cannot for some reason be in React as state (too big, too slow, too whatever). In most cases that's probably a wrong assumption, but it can happen.
I can't create a state object because the state won't be updated whenever the object is
I assume you mean you can't put that object in a React state. We could however put something else in state whenever we want an update. It's the easiest way to trigger a render in React.
Write a function instead of accessing the object directly. That way you can intercept every call that modifies the object. If you can reliably run an observer function when the object changes, that would work too.
Whatever you do, you can't get around calling a function that does something like useState to trigger a render. And you'll have to call it in some way every time you're modifying the object.
const myObject = {};
let i = 0;
let updater = null;
function setMyObject(key, value) {
myObject[key] = value;
i++;
if (updater !== null) {
updater(i);
}
};
Change your code to access the object only with setMyObject(key, value).
You could then put that in a hook. For simplicity I'll assume there's just 1 such object ever on the page.
function useCustomUpdater() {
const [, setState] = useState(0);
useEffect(()=>{
updater = setState;
return () => {
updater = null;
}
}, [setState]);
}
function MyComponent() {
useCustomUpdater();
return <div>I re-render when that object changes</div>;
}
Similarly, as long as you have control over the code that interacts with this object, you could wrap every such call with a function that also schedules an update.
Then, as long as your code properly calls the function, your component will get re-rendered. The only additional state is a single integer.
The question currently lacks too much detail to give a good assessment whether my suggested approach makes sense. But it seems like a very simple way to achieve what you describe.
It would be interesting to get more information about what kind of object it is, how frequently it's updated, and in which scope it lives.
I have created some state at the top level component App() and created a getter method for this state so I could pass it on to any function to be able to get its current state.
App.js
const [searchState, changeScreen] = useState("");
const getSearchState = () => {
console.log("searchState is", searchState);
return searchState;
}
scripts/search.js
export const performSearch = async (searchText, changeScreen, getSearchState) => {
if(searchText) {
console.log("1", getSearchState())
let res = await doSearchQuery(searchText);
console.log("2", getSearchState())
if(res.status) {
// *** getSearchState() should have a value of "loading" here
if(getSearchState() !== "expanded") {
changeScreen("results");
}
}
else {
//
}
}
}
components/SearchComponent.js
import { performSearch } from '../scripts/search';
function SearchHistoryComponent({changeScreen, getSearchState}) {
...
// This method is fired from an onPress()
const performHistorySearch = async (text) => {
changeScreen('loading');
await performSearch(text, changeScreen, getSearchState);
}
...
}
I then pass getSearchState() as a parameter to a standalone asynchronous function in a different script to be able to look up the searchState value but it doesn't seem to be working as intended.
The value I'm getting seems to be the previous value and not the current value at the time getSearchState() is called - as can be seen from the console outputs I have setup:
searchState is expanded
searchState is loading
1 expanded
2 expanded
searchState is results
Am I doing something wrong?
This is exactly how React callback functions work.
That is, every line in your performSearch function is engaged to one searchState value, i.e, "expanded".
If you want to get "loading" from getSearchState(), you need to call getSearchState() again in useEffect by passing searchState or getSearchState in the dependency array.
To be more clear, setting a state value after awaiting a promise works fine, but if you want to pull the newly set state value inside the same function body, it won't work.
That said, you need to listen to the newly set state value in useEffect or just make your code declarative so it behaves according to state changes.
Just to help you understand this better, I've written a quick snack here to show the difference between pulling the state from a function body and a useEffect.
https://snack.expo.dev/h65-cPvIb
Thanks.
I have a problem when using the useEffect hook, it is generating an infinite loop.
I have a list that is loaded as soon as the page is assembled and should also be updated when a new record is found in "developers" state.
See the code:
const [developers, setDevelopers] = useState<DevelopersData[]>([]);
const getDevelopers = async () => {
await api.get('/developers').then(response => {
setDevelopers(response.data);
});
};
// This way, the loop does not happen
useEffect(() => {
getDevelopers();
}, []);
// This way, infinte loop
useEffect(() => {
getDevelopers();
}, [developers]);
console.log(developers)
If I remove the developer dependency on the second parameter of useEffect, the loop does not happen, however, the list is not updated when a new record is found. If I insert "developers" in the second parameter of useEffect, the list is updated automatically, however, it goes into an infinite loop.
What am I doing wrong?
complete code (with component): https://gist.github.com/fredarend/c571d2b2fd88c734997a757bac6ab766
Print:
The dependencies for useEffect use reference equality, not deep equality. (If you need deep equality comparison for some reason, take a look at use-deep-compare-effect.)
The API call always returns a new array object, so its reference/identity is not the same as it was earlier, triggering useEffect to fire the effect again, etc.
Given that nothing else ever calls setDevelopers, i.e. there's no way for developers to change unless it was from the API call triggered by the effect, there's really no actual need to have developers as a dependency to useEffect; you can just have an empty array as deps: useEffect(() => ..., []). The effect will only be called exactly once.
EDIT: Following the comment clarification,
I register a developer in the form on the left [...] I would like the list to be updated as soon as a new dev is registered.
This is one way to do things:
The idea here is that developers is only ever automatically loaded on component mount. When the user adds a new developer via the AddDeveloperForm, we opportunistically update the local developers state while we're posting the new developer to the backend. Whether or not posting fails, we reload the list from the backend to ensure we have the freshest real state.
const DevList: React.FC = () => {
const [developers, setDevelopers] = useState<DevelopersData[]>([]);
const getDevelopers = useCallback(async () => {
await api.get("/developers").then((response) => {
setDevelopers(response.data);
});
}, [setDevelopers]);
useEffect(() => {
getDevelopers();
}, [getDevelopers]);
const onAddDeveloper = useCallback(
async (newDeveloper) => {
const newDevelopers = developers.concat([newDeveloper]);
setDevelopers(newDevelopers);
try {
await postNewDeveloperToAPI(newDeveloper); // TODO: Implement me
} catch (e) {
alert("Oops, failed posting developer information...");
}
getDevelopers();
},
[developers],
);
return (
<>
<AddDeveloperForm onAddDeveloper={onAddDeveloper} />
<DeveloperList developers={developers} />
</>
);
};
The problem is that your getDevelopers function, calls your setDevelopers function, which updates your developers variable. When your developers variable is updated, it triggers the useEffect function
useEffect(() => {
getDevelopers();
}, [developers]);
because developers is one of the dependencies passed to it and the process starts over.
Every time a variable within the array, which is passed as the second argument to useEffect, gets updated, the useEffect function gets triggered
Use an empty array [] in the second parameter of the useEffect.
This causes the code inside to run only on mount of the parent component.
useEffect(() => {
getDevelopers();
}, []);
I don't understand why my useEffect() React function can't access my Component's state variable. I'm trying to create a log when a user abandons creating a listing in our app and navigates to another page. I'm using the useEffect() return method of replicating the componentWillUnmount() lifecycle method. Can you help?
Code Sample
let[progress, setProgress] = React.useState(0)
... user starts building their listing, causing progress to increment ...
console.log(`progress outside useEffect: ${progress}`)
useEffect(() => {
return () => logAbandonListing()
}, [])
const logAbandonListing = () => {
console.log(`progress inside: ${progress}`)
if (progress > 0) {
addToLog(userId)
}
}
Expected Behavior
The code would reach addToLog(), causing this behavior to be logged.
Observed Behavior
This is what happens when a user types something into their listing, causing progress to increment, and then leaves the page.
The useEffect() method works perfectly, and fires the logAbandonListing() function
The first console.log() (above useEffect) logs something greater than 0 for the progress state
The second console.log() logs 0 for the progress state, disabling the code to return true for the if statement and reach the addToLog() function.
Environment
Local dev environment of an app built with Next.js running in Firefox 76.0.1
nextjs v 8.1.0
react v 16.8.6
I'd really appreciate some help understanding what's going on here. Thanks.
I think it is a typical stale closure problem. And it is hard to understand at first.
With the empty dependency array the useEffect will be run only once. And it will access the state from that one run. So it will have a reference from the logAbandonListing function from this moment. This function will access the state from this moment also. You can resolve the problem more than one way.
One of them is to add the state variable to your dependency.
useEffect(() => {
return () => logAbandonListing()
}, [progress])
Another solution is that you set the state value to a ref. And the reference of the ref is not changing, so you will always see the freshest value.
let[progress, setProgress] = React.useState(0);
const progressRef = React.createRef();
progressRef.current = progress;
...
const logAbandonListing = () => {
console.log(`progress inside: ${progressRef.current}`)
if (progressRef.current > 0) {
addToLog(userId)
}
}
If userId is changing too, then you should add it to the dependency or a reference.
To do something in the state's current value in the useEffect's return function where the useEffects dependencies are am empty array [], you could use useReducer. This way you can avoid the stale closure issue and update the state from the useReducer's dispatch function.
Example would be:
import React, { useEffect, useReducer } from "react";
function reducer(state, action) {
switch (action.type) {
case "set":
return action.payload;
case "unMount":
console.log("This note has been closed: " + state); // This note has been closed: 201
break;
default:
throw new Error();
}
}
function NoteEditor({ initialNoteId }) {
const [noteId, dispatch] = useReducer(reducer, initialNoteId);
useEffect(function logBeforeUnMount() {
return () => dispatch({ type: "unMount" });
}, []);
return <div>{noteId}</div>;
}
export default NoteEditor;
More info on this answer
When you return a function from useEffect, it behaves like componentWillUnmount so I think it only runs while cleaning up. You'd need to actually call logAbandonListing like:
useEffect(() => {
logAbandonListing();
}, []);
So it runs everytime a component re-renders. You can read more about useEffect on https://reactjs.org/docs/hooks-effect.html
It's written excellently.
I tried using this sandbox to explain my answer.
Basically you are returning a function from your useEffect Callback. But that returned function is never really invoked so it does no actually execute and thus log the abandon action. If you look at the Code in the sandbox I have added a wrapper Parens and () afterwards to actually cause the method to be invoked leading to console.log executing.
I've been playing around with the new hook system in React 16.7-alpha and get stuck in an infinite loop in useEffect when the state I'm handling is an object or array.
First, I use useState and initiate it with an empty object like this:
const [obj, setObj] = useState({});
Then, in useEffect, I use setObj to set it to an empty object again. As a second argument I'm passing [obj], hoping that it wont update if the content of the object hasn't changed. But it keeps updating. I guess because no matter the content, these are always different objects making React thinking it keep changing?
useEffect(() => {
setIngredients({});
}, [ingredients]);
The same is true with arrays, but as a primitive it wont get stuck in a loop, as expected.
Using these new hooks, how should I handle objects and array when checking weather the content has changed or not?
Passing an empty array as the second argument to useEffect makes it only run on mount and unmount, thus stopping any infinite loops.
useEffect(() => {
setIngredients({});
}, []);
This was clarified to me in the blog post on React hooks at https://www.robinwieruch.de/react-hooks/
Had the same problem. I don't know why they not mention this in docs. Just want to add a little to Tobias Haugen answer.
To run in every component/parent rerender you need to use:
useEffect(() => {
// don't know where it can be used :/
})
To run anything only one time after component mount(will be rendered once) you need to use:
useEffect(() => {
// do anything only one time if you pass empty array []
// keep in mind, that component will be rendered one time (with default values) before we get here
}, [] )
To run anything one time on component mount and on data/data2 change:
const [data, setData] = useState(false)
const [data2, setData2] = useState('default value for first render')
useEffect(() => {
// if you pass some variable, than component will rerender after component mount one time and second time if this(in my case data or data2) is changed
// if your data is object and you want to trigger this when property of object changed, clone object like this let clone = JSON.parse(JSON.stringify(data)), change it clone.prop = 2 and setData(clone).
// if you do like this 'data.prop=2' without cloning useEffect will not be triggered, because link to data object in momory doesn't changed, even if object changed (as i understand this)
}, [data, data2] )
How i use it most of the time:
export default function Book({id}) {
const [book, bookSet] = useState(false)
const loadBookFromServer = useCallback(async () => {
let response = await fetch('api/book/' + id)
response = await response.json()
bookSet(response)
}, [id]) // every time id changed, new book will be loaded
useEffect(() => {
loadBookFromServer()
}, [loadBookFromServer]) // useEffect will run once and when id changes
if (!book) return false //first render, when useEffect did't triggered yet we will return false
return <div>{JSON.stringify(book)}</div>
}
I ran into the same problem too once and I fixed it by making sure I pass primitive values in the second argument [].
If you pass an object, React will store only the reference to the object and run the effect when the reference changes, which is usually every singe time (I don't now how though).
The solution is to pass the values in the object. You can try,
const obj = { keyA: 'a', keyB: 'b' }
useEffect(() => {
// do something
}, [Object.values(obj)]);
or
const obj = { keyA: 'a', keyB: 'b' }
useEffect(() => {
// do something
}, [obj.keyA, obj.keyB]);
If you are building a custom hook, you can sometimes cause an infinite loop with default as follows
function useMyBadHook(values = {}) {
useEffect(()=> {
/* This runs every render, if values is undefined */
},
[values]
)
}
The fix is to use the same object instead of creating a new one on every function call:
const defaultValues = {};
function useMyBadHook(values = defaultValues) {
useEffect(()=> {
/* This runs on first call and when values change */
},
[values]
)
}
If you are encountering this in your component code the loop may get fixed if you use defaultProps instead of ES6 default values
function MyComponent({values}) {
useEffect(()=> {
/* do stuff*/
},[values]
)
return null; /* stuff */
}
MyComponent.defaultProps = {
values = {}
}
Your infinite loop is due to circularity
useEffect(() => {
setIngredients({});
}, [ingredients]);
setIngredients({}); will change the value of ingredients(will return a new reference each time), which will run setIngredients({}). To solve this you can use either approach:
Pass a different second argument to useEffect
const timeToChangeIngrediants = .....
useEffect(() => {
setIngredients({});
}, [timeToChangeIngrediants ]);
setIngrediants will run when timeToChangeIngrediants has changed.
I'm not sure what use case justifies change ingrediants once it has been changed. But if it is the case, you pass Object.values(ingrediants) as a second argument to useEffect.
useEffect(() => {
setIngredients({});
}, Object.values(ingrediants));
As said in the documentation (https://reactjs.org/docs/hooks-effect.html), the useEffect hook is meant to be used when you want some code to be executed after every render. From the docs:
Does useEffect run after every render? Yes!
If you want to customize this, you can follow the instructions that appear later in the same page (https://reactjs.org/docs/hooks-effect.html#tip-optimizing-performance-by-skipping-effects). Basically, the useEffect method accepts a second argument, that React will examine to determine if the effect has to be triggered again or not.
useEffect(() => {
document.title = `You clicked ${count} times`;
}, [count]); // Only re-run the effect if count changes
You can pass any object as the second argument. If this object remains unchanged, your effect will only be triggered after the first mount. If the object changes, the effect will be triggered again.
I'm not sure if this will work for you but you could try adding .length like this:
useEffect(() => {
// fetch from server and set as obj
}, [obj.length]);
In my case (I was fetching an array!) it fetched data on mount, then again only on change and it didn't go into a loop.
If you include empty array at the end of useEffect:
useEffect(()=>{
setText(text);
},[])
It would run once.
If you include also parameter on array:
useEffect(()=>{
setText(text);
},[text])
It would run whenever text parameter change.
I often run into an infinite re-render when having a complex object as state and updating it from useRef:
const [ingredients, setIngredients] = useState({});
useEffect(() => {
setIngredients({
...ingredients,
newIngedient: { ... }
});
}, [ingredients]);
In this case eslint(react-hooks/exhaustive-deps) forces me (correctly) to add ingredients to the dependency array. However, this results in an infinite re-render. Unlike what some say in this thread, this is correct, and you can't get away with putting ingredients.someKey or ingredients.length into the dependency array.
The solution is that setters provide the old value that you can refer to. You should use this, rather than referring to ingredients directly:
const [ingredients, setIngredients] = useState({});
useEffect(() => {
setIngredients(oldIngedients => {
return {
...oldIngedients,
newIngedient: { ... }
}
});
}, []);
If you use this optimization, make sure the array includes all values from the component scope (such as props and state) that change over time and that are used by the effect.
I believe they are trying to express the possibility that one could be using stale data, and to be aware of this. It doesn't matter the type of values we send in the array for the second argument as long as we know that if any of those values change it will execute the effect. If we are using ingredients as part of the computation within the effect, we should include it in the array.
const [ingredients, setIngredients] = useState({});
// This will be an infinite loop, because by shallow comparison ingredients !== {}
useEffect(() => {
setIngredients({});
}, [ingredients]);
// If we need to update ingredients then we need to manually confirm
// that it is actually different by deep comparison.
useEffect(() => {
if (is(<similar_object>, ingredients) {
return;
}
setIngredients(<similar_object>);
}, [ingredients]);
The main problem is that useEffect compares the incoming value with the current value shallowly. This means that these two values compared using '===' comparison which only checks for object references and although array and object values are the same it treats them to be two different objects. I recommend you to check out my article about useEffect as a lifecycle methods.
The best way is to compare previous value with current value by using usePrevious() and _.isEqual() from Lodash.
Import isEqual and useRef. Compare your previous value with current value inside the useEffect(). If they are same do nothing else update. usePrevious(value) is a custom hook which create a ref with useRef().
Below is snippet of my code. I was facing problem of infinite loop with updating data using firebase hook
import React, { useState, useEffect, useRef } from 'react'
import 'firebase/database'
import { Redirect } from 'react-router-dom'
import { isEqual } from 'lodash'
import {
useUserStatistics
} from '../../hooks/firebase-hooks'
export function TMDPage({ match, history, location }) {
const usePrevious = value => {
const ref = useRef()
useEffect(() => {
ref.current = value
})
return ref.current
}
const userId = match.params ? match.params.id : ''
const teamId = location.state ? location.state.teamId : ''
const [userStatistics] = useUserStatistics(userId, teamId)
const previousUserStatistics = usePrevious(userStatistics)
useEffect(() => {
if (
!isEqual(userStatistics, previousUserStatistics)
) {
doSomething()
}
})
In case you DO need to compare the object and when it is updated here is a deepCompare hook for comparison. The accepted answer surely does not address that. Having an [] array is suitable if you need the effect to run only once when mounted.
Also, other voted answers only address a check for primitive types by doing obj.value or something similar to first get to the level where it is not nested. This may not be the best case for deeply nested objects.
So here is one that will work in all cases.
import { DependencyList } from "react";
const useDeepCompare = (
value: DependencyList | undefined
): DependencyList | undefined => {
const ref = useRef<DependencyList | undefined>();
if (!isEqual(ref.current, value)) {
ref.current = value;
}
return ref.current;
};
You can use the same in useEffect hook
React.useEffect(() => {
setState(state);
}, useDeepCompare([state]));
You could also destructure the object in the dependency array, meaning the state would only update when certain parts of the object updated.
For the sake of this example, let's say the ingredients contained carrots, we could pass that to the dependency, and only if carrots changed, would the state update.
You could then take this further and only update the number of carrots at certain points, thus controlling when the state would update and avoiding an infinite loop.
useEffect(() => {
setIngredients({});
}, [ingredients.carrots]);
An example of when something like this could be used is when a user logs into a website. When they log in, we could destructure the user object to extract their cookie and permission role, and update the state of the app accordingly.
my Case was special on encountering an infinite loop, the senario was like this:
I had an Object, lets say objX that comes from props and i was destructuring it in props like:
const { something: { somePropery } } = ObjX
and i used the somePropery as a dependency to my useEffect like:
useEffect(() => {
// ...
}, [somePropery])
and it caused me an infinite loop, i tried to handle this by passing the whole something as a dependency and it worked properly.
Another worked solution that I used for arrays state is:
useEffect(() => {
setIngredients(ingredients.length ? ingredients : null);
}, [ingredients]);