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 realise there are probably a million and one different causes for this error but I am struggling to find the cause of mine. I am relatively new to Redux and state handling in the Reducer and have learned from a few examples online to come up with the code sample below which is called within the Reducer:
const updateTripsWhereVenueDeleted = (state, action) => {
debugger;
const deletedVenueId = action.venue.Id;
const originalTrips = [...state];
const newTrips = originalTrips.map((trip) => {
if (trip.VenueId === deletedVenueId) {
trip.VenueId = 0;
trip.VenuePegId = 0;
}
return trip;
});
debugger;
return [...newTrips];
};
I have state which is an array of Trips:
And Action contains a 'Venue' record.
Basically, the Venue being passed was deleted and I want to update the relevant fields on all Trips that reference the deleted Venue.
When I run the above code in the Reducer things seem to go in the right direction until the browser crashes with the following error:
Unhandled Rejection (Invariant Violation): A state mutation was
detected inside a dispatch, in the path: trips.0.VenueId. Take a
look at the reducer(s) handling the action
{"type":"UPDATE_TRIPS_VENUE_DELETED","venue": {.... the object}
UPDATE_TRIPS_VENUE_DELETED is the action.type that calls my method above.
Is there an obvious mis-use of handling (spread) arrays in a state or something. I feel this should be an easy thing to do but nothing I have tried has so far worked correctly.
Spreading an object or array ([...state] here) does not break nested references. So you are mutating state by not making a copy of the nested object within your map -- trip.VenueId = 0;.
This leads to another observation, map returns a new array, so this negates the need to use originalTrips altogether. It is just as safe to do state.map(). The final spread [...newTrips] is definitely unnecessary as well.
To fix your mutation create a clone of the objects to be updated:
const updateTripsWhereVenueDeleted = (state, action) => {
const deletedVenueId = action.venue.Id;
const newTrips = state.map((trip) => {
if (trip.VenueId === deletedVenueId) {
// Copy other trip values into NEW object and return it
return { ...trip, VenueId: 0, VenuePegId: 0 };
}
// If not matched above, just return the old trip
return trip;
});
return newTrips;
};
Spread operator ... only does shallow copy. If the array is nested or multi-dimensional, it won't work.
There are plenty of way we can do this, below are some of them
1] Deep copy using JSON
const originalTrips = JSON.parse(JSON.stringify(state));;
2]
const newTrips = originalTrips.map((trip) => {
if (newTrip.VenueId === deletedVenueId) {
let newTrip = Object.assign({},trip);
newTrip.VenueId = 0;
newTrip.VenuePegId = 0;
return newTrip;
}
return trip;
});
I know we are not supposed to mutate a state object directly. Does this apply to the state object available in the call back of setState. I am looking to avoid using the spread operator too much. For example, can we do the following
setState(prevState => {
prevState.count += 1;
prevState.data.list[0].item.prop = 34;
return prevState;
});
you should always make copies from objects you modify to update state, otherwise you will face bugs in your application since you have the same reference. Each part of state you modify you should make a copy, which in really nested states could be difficult.
One thing advisable is to flat your state if you can. This way you avoid really nested states, which would lead to multiple copies and prone to error. Your example, it looks you could have 2 different states count and items:
const [count, setCount] = useState(0);
const [items, setItems] = useState(dataItems);
// some update state function logic call
setCount(count => ++count);
setItems(items => {
const nextItems = [...items]; // new arrray copy
nextItems[0] = { ...nextItems[0], prop: 34}; // new copy obj
return nextItems;
});
otherwise your state update would look like:
setState(prevState => {
const nextState = { ...prevState }
nextState.count += 1;
nextState.data = { ...nextState.data }
nextState.data.list = [ ...nextData.data.list ]
const item = nextState.data.list[0]
nextState.data.list[0].item = { ...nextState.data.list[0].item , prop: 34 };
return nextState;
});
I have a React component which receives data from a parent.
Now, this data is dynamic and I do not know beforehand what the properties are called exactly.
I need to render them in a certain fashion and that all works perfectly fine.
Now though, these dynamic objects have a property which is a number, which has to be displayed in my component.
To do so, I thought while iterating over the data, I will add the values to the sum, which is to be displayed. Whenever one of the data object changes, the sum will change, too (since I am using useState and React will detect that change.
But that exactly is the problem I don't know how to solve.
It is obvious that right now my code generates an infinite-loop:
The component is created and rendered for the first time.
During this process, setSum() is called, and therefore changing the state.
React detects that and orders a re-rendering.
So how do I fix this? I feel like I am missing something quite obvious here, but I am too invested to see it.
I have tried to boil down my code to the most easy to read code snippet which focuses on the problem only. Any suggestions to improve the readabilty are welcome!
const ComponentA = (data) => {
const [sum, setSum] = React.useState(0);
const renderData = (dataToRender) => {
//Here lies the problem already
setSum(0)
const result = [];
dataToRender.forEach((objData, index) => {
result.push(<JSX Item>Content</JSX Item>);
//and some more stuff, not relevant
// will not get this far
const newSum = sum+objData.propertyAmount;
setSum(newSum);
});
return result;
};
return(
//...someJSXElements
{data.relevantObjectArray && renderData(data.relevantObjectArray)}
<div>{sum}</div>
);
}
The reason it's re-rendering infinitely is because you are setting the state every time the component is rendered, which subsequently triggers another re-render. What you need to do is separate your display code from your state-setting code. I initially thought that useEffect would be a good solution (you can see the edit history for my original answer), however from the React docs:
useReducer is usually preferable to useState when you have complex state logic that involves multiple sub-values or when the next state depends on the previous one. (React docs)
So you could therefore try something like this:
const reducer = (sum, action) => {
switch (action.type) {
case "increment":
return sum + action.propertyAmount;
default:
throw new Error();
}
};
const initialSum = 0;
const ComponentA = (data) => {
const [sum, sumReducer] = React.useReducer(reducer, initialSum);
React.useEffect(() => {
data.relevantObjectArray.forEach((objData, index) => {
sumReducer({ type: "increment", propertyAmount: objData.propertyAmount });
});
}, [data.relevantObjectArray]);
const renderData = (dataToRender) => {
const result = [];
dataToRender.forEach((objData, index) => {
result.push(<div>Content</div>);
});
return result;
};
return (
<div>
{data.relevantObjectArray && renderData(data.relevantObjectArray)}
<div>{sum}</div>
</div>
);
};
Example on codesandbox.io.
const ComponentA = (data) => {
const [sum, setSum] = React.useState(0);
const renderData = (dataToRender) => {
//Here lies the problem already
setSum(0)
const result = [];
dataToRender.forEach((objData, index) => {
result.push(<JSX Item>Content</JSX Item>);
//and some more stuff, not relevant
// will not get this far
const newSum = sum+objData.propertyAmount;
setSum(newSum);
});
return result;
};
React.useEffect(() => {
renderData();
return () => {
console.log('UseEffect cleanup')});
}, [data);
return(
//...someJSXElements
//The line below is causing the continuos re-render because you keep calling the function (renderData)
//{data.relevantObjectArray && renderData(data.relevantObjectArray)}
<div>{sum}</div>
);
}
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]);