I have problem with me code because in useCallback function always is shown state outdated, pre-last one.
In useEffect(()) I do console.log, and I can see the change of state, but in second function it shown only when it is click two times. It is not the way I can do something.
import produce from Immer;
const [obiektPompa, setObiektPompa] = useState([]);
const [modulPV, setModulPV] = useState([]);
function setDodatkowe(e, index) {
e.preventDefault();
const {cena, nazwa} = formData.current;
const newProduct = {nazwa: nazwa.value,
cena: parseFloat(cena.value)
}
setObiektPompa((prevState) => ([...prevState, newProduct ]))
console.log("zmiana Pomp", obiektPompa)
AddItemPrice(index)
}
useEffect(() => {
console.log("obiekt Pompa z useEffect", obiektPompa) //Console.log state
}, [obiektPompa])
const AddItemPrice = useCallback ((index ) => {
setModulyPV(
produce( modulyPV, draft => {
const objIndex = draft.findIndex((obj => obj.index === index));
const value = obiektPompa[obiektPompa.length -1].cena
console.log("index", draft[index].cena)
console.log("Vaalue pompa", value)
})
)
}, [modulyPV, setModulyPV, setDodatkowe, setObiektPompa, obiektPompa])
Needless to say that I put useRef hook the value from setDodatkowe is from submit property of button.
Problem is with obiektPompa which is useState, and as you see in useEffect show me everything, but in useCallback do not.
In AddItemPrice I tried to add dependence formData.current.onsubmit but it do not give result.
Related
In my React functional components, I am trying to use custom usePrevious to get/compare the previous value of my context object. However, it seems to be having the latest value always and not the previous value. Below is my code. Please let me know if I am doing something wrong here.
function MyHeaderComponent(props) {
const [myPref, setMyPref] = React.useContext(MyContext);
const prevPreferences = usePrevious(myPref.preferences);
useEffect(() => {
console.log("prevPreferences : " + prevPreferences); // Prints current context object, instead of the previous one
// I want to call myInfo only if prevPreferences is not the same as myPref.preferences (i.e. current)
}, [myPref]);
function usePrevious(value) {
const ref = useRef();
useEffect(() => {
ref.current = value;
});
return ref.current;
}
const myInfo = async () => {
setMyPref(myPref);
}
return (
<>
<div>
Some JSX
</div>
</>
)
}
export default withRouter(withStyles()(MyHeaderComponent));
function MyPreferences(props) {
const [myPref, setMyPref] = React.useContext(MyContext);
// somewhere in code
setMyPref(myPref);
}
That implementation of useLatest (which should not be within the component, by the way) does not copy the value into the ref box, it just assigns a reference.
I'd wager myPref.preferences gets internally modified (instead of being reassigned a new object), which is why you always see the same value.
I think the problem is you are using usePrevious hook inside another functional component. Could you try to create a file for the usePrevious hook.
usePreviousState.js
function usePrevious(value, initialValue) {
const ref = useRef();
useEffect(() => {
ref.current = value;
}, [value]);
if (ref.current === undefined && initialValue !== undefined) {
return initialValue;
}
return ref.current;
}
Trying to detect if a <section> element is focused in viewport, I'm unable console.log a single true statement. I'm implementing a [isFocused, setIsFocused] hook for this.
This is my window:
I needed so when Section 2 is positioned at the top of the window, a single console.log(true) shows up. But this happens:
This is my implementation:
import React, { useEffect, useRef, useState } from "react";
const SectionII = (props) => {
const sectionRef = useRef();
const [isFocused, setIsFocused] = useState(false);
const handleScroll = () => {
const section = sectionRef.current;
const { y } = section.getBoundingClientRect();
if(!isFocused && y <= 0) {
setIsFocused(true);
console.log(isFocused, y);
}
};
useEffect(() => {
window.addEventListener('scroll', handleScroll);
return () => window.removeEventListener('scroll', handleScroll);
}, []);
return (
<section id="mentorship" ref={sectionRef} style={{borderTop: "1px solid"}}>
<h1>Section 2</h1>
<button>Set hash</button>
</section>
);
};
export default SectionII;
Why wouldn't my state by updated to true with setIsFocused(true) inside if(!isFocused && y <= 0)?
Thanks so much for the insight. I'm really stuck.
When you're using any state management in react, you need to ensure that the change is set before attempting to access the new state value. For your example, you immediately console.log(isFocused, y) following your setState function (changes will only appear on the next DOM render). Rather, you should use a callback with the set state function, setIsFocused(true, () => console.log(isFocused, y)).
I am trying to sort an array and reflect its sort result immediately by useState hook.
I already new that react is detecting its state change by Object.is(), so trying to spread array before using useState like below;
const [reviews, setReviews] = useState([...book.reviews]);
useEffect(() => {
const sortedReviews = [...reviews]
.sort((review1: IReview, review2: IReview) =>
sortBy(review1, review2, sortRule));
setReviews([...sortedReviews])
}, [sortRule])
After sorting I checked the value of variable sortedReviews and it was sorted as expected, but react did not re-render the page so this sorting was not reflected to UI.
I already searched solutions and it seemed many could solve the issue by spreading an array to before calling useState like this stack overflow is explaining: Why is useState not triggering re-render?.
However, on my end it is not working.. Any help will be very appreciated. Thank you!
[Added]
And my rendering part is like below;
<>
{
sortedReviews
.map((review: IReview) => (
<ReviewBlock id={review.id}
review={review}
targetBook={book}
setTargetBook={setBook}/>
))
}
</>
Sometimes I facing this issue too, in my case I just "force" render calling callback.
First solution:
const [reviews, setReviews] = useState([...book.reviews]);
useEffect(() => {
const sortedReviews = [...reviews]
.sort((review1: IReview, review2: IReview) =>
sortBy(review1, review2, sortRule));
setReviews(()=> [...sortedReviews]) // <-- Here
}, [sortRule])
second solution:
You can use useRef to get data in real time, see below:
const [reviews, setReviews] = useState([...book.reviews]);
const reviewsRef = useRef();
useEffect(() => {
const sortedReviews = [...reviews]
.sort((review1: IReview, review2: IReview) =>
sortBy(review1, review2, sortRule));
setReviewRef([...sortedReviews])
}, [sortRule])
function setReviewRef(data){
setReview(data);
reviewsRef.current = data;
}
So, instead use the state reviews use reviewsRef.current as u array
I hope you can solve this!
When components don't re-render it is almost always due to mutations of state. Here you are calling a mutating operation .sort on reviews. You would need to spread the array before you mutate it.
useEffect(() => {
const sortedReviews = [...reviews].sort((review1: IReview, review2: IReview) =>
sortBy(review1, review2, sortRule)
);
setReviews(sortedReviews);
}, [sortRule]);
But there are other issues here. reviews is not a dependency of the useEffect so we would want to use a setReviews callback like setReviews(current => [...current].sort(....
In general sorted data makes more sense as a useMemo than a useState. The sortRule is a state and the sortedReviews are derived from it.
The way that you are calling sortBy as a comparer function feels a bit off. Maybe it's just a confusing name?
Also you should not need to include the type IReview in your callback if book is typed correctly as {reviews: IReview[]}.
If you include your sortBy function and sortRule variable then I can be of more help. But here's what I came up with.
import React, { useState, useMemo } from "react";
type IReview = {
rating: number;
}
type Book = {
reviews: IReview[]
}
type SortRule = string; // just a placeholder - what is this really?
declare function sortBy(a: IReview, b: IReview, rule: SortRule): number;
const MyComponent = ({book}: {book: Book}) => {
const [sortRule, setSortRule] = useState("");
const reviews = book.reviews;
const sortedReviews = useMemo( () => {
return [...reviews].sort((review1, review2) =>
sortBy(review1, review2, sortRule)
);
}, [sortRule, reviews]);
...
}
Typescript Playground Link
I'm noticing something really strange while working with hooks, I've got the following:
import React, { useState, useEffect } from "react";
const [dependency1, setDependency1] = useState({});
const [dependency2, setDependency2] = useState([]);
useEffect(() => {
console.log("dependency 1 got an update");
}, [dependency1]);
useEffect(() => {
console.log("dependency 2 got an update");
}, [dependency2]);
setInterval(() => {
setDependency1(prevDep1 => {
const _key = "test_" + Math.random().toString();
if (prevDep1[_key] === undefined) prevDep1[_key] = [];
else prevDep1[key].push("foo");
return prevDep1;
})
setDependency2(prevDep2 => [...prevDep2, Math.random()]);
}, 1000);
for some reason only the useEffect with dependency2 (the array where items get added) triggers, the one with dependency1 (the object where keys get added) doesn't trigger..
Why is this happening, and how can I make it work?
setInterval(() => {
setDependency1(prevDep1 => {
const _key = "test_" + Math.random().toString();
return {...prevDep1, [_key]: [...(prevDep1[_key] || []), 'foo'] }
})
setDependency2(prevDep2 => [...prevDep2, Math.random()]);
}, 1000);
State should be updated in an immutable way.
React will only check for reference equality when deciding a dependency changed, so if the old and new values pass a === check, it considers it unchanged.
In your first dependency you simply added a key to the existing object, thus not changing the actual object. The second dependency actually gets replaced altogether when spreading the old values into a new array.
You're returning an assignment statement here:
setDependency1(prevDep1 => prevDep1["test_" + Math.random().toString()] = ["foo"]);
You should return an object. Maybe something like:
setDependency1(prevDep1 => ({ ...prevDep1, ["test_" + Math.random().toString()]: ["foo"] }));
Considering the following declaration:
const [stateObject, setObjectState] = useState({
firstKey: '',
secondKey: '',
});
Are the following snippets both corrects ?
A)
setObjectState((prevState) => ({
...prevState,
secondKey: 'value',
}));
B)
setObjectState({
...stateObject,
secondKey: 'value',
}));
I am sure that A) is correct, but is it necessary ? B) seems ok, but as setObjectState is an asynchronous function, stateObject might not have the most recent value.
One useful thing about case of A that I have found is that you can use this method to update state from child components while only passing down a single prop for setObjectState. For example, say you have parent component with state you would like to update from the child component.
Parent Component:
import React, {useState} from 'react';
import ChildComponent from './ChildComponent';
export const ParentComponent = () => {
const [parentState, setParentState] = useState({
otherValue: null,
pressed: false,
});
return (
<ChildComponent setParentState={setParentState} />
)
}
Child Component:
import React from 'react';
export const ChildComponent = (props) => {
const callback = () => {
props.setParentState((prevState) => ({
...prevState
pressed: true,
}))
}
return (
<button onClick={callback}>test button<button>
)
}
When the button is pressed, you should expect to see that the state has been updated while also keeping its initial values. As for the difference between the two, there isn't much as they both accomplish the same thing.
A will always give you the updated value. B could be correct but might not. Let me give an example:
const Example = props => {
const [counter, setCounter] = useState(0);
useEffect(() => {
// 0 + 1
// In this first case the passed value would be the same as using the callback.
// This is because in this cycle nothing has updated counter before this point.
setCounter(counter + 1);
// 1 + 1
// Thanks to the callback we can get the current value
// which after the previous iexample is 1.
setCounter(latest_value => latest_value + 1);
// 0 + 1
// In this case the value will be undesired as it is using the initial
// counter value which was 0.
setCounter(counter + 1);
}, []);
return null;
};
When the new value depends on the updated one use the callback, otherwise you can simply pass the new value.
const Example = props => {
const [hero, setHero] = useState('Spiderman');
useEffect(() => {
// Fine to set the value directly as
// the new value does not depend on the previous one.
setHero('Batman');
// Using the callback here is not necessary.
setHero(previous_hero => 'Superman');
}, []);
return null;
};
Also in the example you are giving it would probably be better to use two different states:
const [firstKey, setFirstKey] = useState("");
const [secondKey, setSecondKey] = useState("");