I have the following setup:
const templates = [
'dot',
'line',
'circle',
'square',
];
const [currentTemplate, setCurrentTemplate] = useState(0);
const changeTemplate = (forward = true) => {
let index = currentTemplate;
index = forward ? index + 1 : index - 1;
if (index > templates.length - 1) {
index = 0;
} else if (index < 0) {
index = templates.length - 1;
}
setCurrentTemplate(index);
};
useEffect(() => {
console.log(`Current Template is: ${templates[currentTemplate]}`);
}, [currentTemplate]);
useKeypress('ArrowLeft', () => {
changeTemplate(false);
});
useKeypress('ArrowRight', () => {
changeTemplate(true);
});
This is the useKeypress-Hook is used:
import { useEffect } from 'react';
/**
* useKeyPress
* #param {string} key - the name of the key to respond to, compared against event.key
* #param {function} action - the action to perform on key press
*/
export default function useKeypress(key: string, action: () => void) {
useEffect(() => {
function onKeyup(e: KeyboardEvent) {
if (e.key === key) action();
}
window.addEventListener('keyup', onKeyup);
return () => window.removeEventListener('keyup', onKeyup);
}, []);
}
Whenever I press the left or right arrow key, the function gets triggered. But the currentTemplate variable is not changing. It always stays at 0. The useEffect is only triggered when I swich the key from left to right or the other way. Clicking the same key twice, does not trigger useEffect again, but it should! When changing from right to left, the output is Current Template is: square and when changing from left to right, it is Current Template is: line. But this never changes. The value of currentTemplate always stays 0.
What am I missing?
The issue is with your useEffect inside the useKeypress hook.
export default function useKeypress(key: string, action: () => void) {
useEffect(() => {
function onKeyup(e: KeyboardEvent) {
if (e.key === key) action();
}
window.addEventListener('keyup', onKeyup);
return () => window.removeEventListener('keyup', onKeyup);
}, []); // 👈 problem
}
The hook is a single useEffect with no dependencies. Meaning, it will only fire once. This is a problem for the action you are passing into this hook. Whenever the changeTemplate-action changes in your component (i.e. on a rerender), the reference to this is not renewed inside of the useKeypress-hook.
To solve this, you need to add the action to the dependency array of the useEffect:
export default function useKeypress(key: string, action: () => void) {
useEffect(() => {
function onKeyup(e: KeyboardEvent) {
if (e.key === key) action();
}
window.addEventListener('keyup', onKeyup);
return () => window.removeEventListener('keyup', onKeyup);
}, [action]); // 👈 whenever `action` changes, the effect will be updated
}
This is to ensure that the effect is updated whenever the given action is changed. After this change, things should be working as expected.
Optimalizing:
The useEffect will at this point be regenerated for each render, as the changeTemplate function will be instanciated for each render. To avoid this, you can wrap the changeTemplate with a useCallback, so that the function is memoized:
const changeTemplate = useCallback(
(forward = true) => {
let index = currentTemplate;
index = forward ? index + 1 : index - 1;
if (index > templates.length - 1) {
index = 0;
} else if (index < 0) {
index = templates.length - 1;
}
setCurrentTemplate(index);
},
// Regenerate the callback whenever `currentTemplate` or `setCurrentTemplate` changes
[currentTemplate, setCurrentTemplate]
);
Related
I have a group of functions that are responsible for adding and removing sections from my form in my app. I use a counter (subjectAddressCounter) in my state that keeps track of the iteration of the section being added. This works as expected when the user clicks the buttons to add and remove the sections, however when I call the addSection() function on init in a form mapping function generateAdditiveFormKeys() the counter jumps from 0 to 2 and so it only calls the callback function in the useEffect responsible for adding the section one time, which means my form doesn't build correctly.
So to be clear. I expect that for each time the function is called the counter will iterate by one, but what's happening on init is that my function is called twice, but in the useEffect the counter goes from 0 to 2 instead of 0, 1, 2. This causes my callback function to only be called once and then the sections are out of sync.
What am I doing wrong?
Please see the relevant code below. Also, is there a way to simplify this pattern so I don't need to use three functions just to add or remove a section?
const FormGroup = prop => {
const [subjectAddressCounter, setSubjectAddressCounter] = useState(0);
const addValues = () => {
const newSection = subjectAddressCopy.map(copy => {
const clone = {
...copy,
prop: copy.prop = `${copy.prop}_copy_${subjectAddressCounter}`,
multiTypes: copy.multiTypes ? copy.multiTypes.map(multi => {
const cloneMultiTypes = {
...multi,
prop: multi.prop = `${multi.prop}_copy_${subjectAddressCounter}`,
};
return cloneMultiTypes;
}) : null,
};
return clone;
});
...
};
const removeValues = () => {
...
}
const prevSubjectAddressCounterRef = useRef<number>(subjectAddressCounter);
useEffect(() => {
prevSubjectAddressCounterRef.current = subjectAddressCounter;
if (prevSubjectAddressCounterRef.current < subjectAddressCounter) {
// call function to addValues
// this is only being called once on init even though subjectAddressCounter starts at 0 and goes to 2
addValues();
}
if (prevSubjectAddressCounterRef.current > subjectAddressCounter) {
// call function to removeValues
removeValues();
}
}, [subjectAddressCounter]);
const addSection = section => {
if (section.section === SectionTitle.subjectAddress) {
// this gets called twice on init
setSubjectAddressCounter(prevCount => prevCount + 1);
}
};
const removeSection = section => {
if (section.section === SectionTitle.subjectAddress) {
setSubjectAddressCounter(prevCount => prevCount - 1);
}
};
const generateAdditiveFormKeys = reportResponse => {
const {
entity_addresses_encrypted: entityAddressesEncrypted, // length equals 3
} = reportResponse;
let additiveAddresses = {};
if (entityAddressesEncrypted?.length > 1) {
entityAddressesEncrypted.forEach((entityAddress, i) => {
if (i === 0) return;
if (subjectAddressCounter < entityAddressesEncrypted.length - 1) {
addSection({ section: SectionTitle.subjectAddress });
}
const keysToAdd = {
[`question_11_address_copy_${i - 1}`]: entityAddress.address,
[`question_12_city_copy_${i - 1}`]: entityAddress.city,
[`question_13_state_copy_${i - 1}`]: entityAddress.state,
[`question_14_zip_copy_${i - 1}`]: entityAddress.zip,
[`question_15_country_copy_${i - 1}`]: entityAddress.country,
};
additiveAddresses = { ...additiveAddresses, ...keysToAdd };
});
}
...
}
return (
...
button onClick={() => addSection(form)}
button onClick={() => removeSection(form)}
)
}
I'm trying to setup an onKeyPress event listener and I'm confused as to why the initial value is undefined and then the value I want. The data is added on mount (see x in console). Why am I unable to immediately capture it and instead get an initial undefined, especially since it clearly already exists in state?
useEffect(() => {
console.log('x', multipleChoice); <-- logs the array of objects
const handleKeyPress = ({ key }) => {
const index = Number(key) - 1;
if (key === '1') {
console.log(multipleChoice[index]); <-- logs undefined, then logs object
}
};
window.addEventListener('keydown', (e) => handleKeyPress(e));
return () => {
window.removeEventListener('keydown', (e) => handleKeyPress(e));
};
}, [allCards, currentCard, multipleChoice]);
LocalState
const [currentCard, setCard] = useState(0);
const [multipleChoice, setMultipleChoice] = useState([]);
// allCards is passed as a prop on page load from the parent
When the user guesses an answer correctly the currentCard is incremented by 1
UseEffect that sets multipleChoice
useEffect(() => {
const generateMultipleChoice = (words: Word[]) => {
const possibleAnswers = words.reduce(
(accum: Word[]) => {
while (accum.length < 4) {
// randomly select words from pool
const index = getRandomInt(0, allCards.length - 1);
const randomWord = allCards[index];
// verify current hand doesn't already have that word
if (!accum.includes(randomWord)) {
accum.push(randomWord);
}
}
return accum;
},
// default with the current card already in the hand
[allCards[currentCard]]
);
// return the hand with the matching card and (3) other cards from pool
return possibleAnswers;
};
const shuffledCards = shuffle(generateMultipleChoice(allCards));
setMultipleChoice(shuffledCards);
}, [allCards, currentCard]);
screenshot of console
This is it:
// initial state
const [multipleChoice, setMultipleChoice] = useState([]);
// therefore, initially, if index is any Number
console.log(multipleChoice[index]) // undefined
The object is returned, only until the calculation is finished...
useEffect(() => {
// ...
// this has to run before `multipleChoice` is updated to return that object
const shuffledCards = shuffle(generateMultipleChoice(allCards));
setMultipleChoice(shuffledCards);
}, [allCards, currentCard]);
In my current I am was trying to check if the latest index (number 5) jumps to 1. Since I have built a function counter that automatically jumps to 1 when it reach the latest index, but I also want to have a check when it jumps from latest index to the first index...React Hook not necessarily needed for this issue....
const App = ({ scoreCounter }) => {
const boolean = useRef(null);
const [ checkCounter, setCheckCounter ] = useState(false);
useEffect(() => {
const storedCounter = currentCounter;
boolean.current = storedCounter;
return () => storedCounter;
}, []);
useEffect(() => {
if(currentCounter == 5) {
}
console.log(boolean.current, currentCounter);
}, [boolean.current, currentCounter])
}
const mapStateToProps = state => {
return {
currentCounter: state.game.counter
}
}
If you're using class components you can compare your prevState to your current state in the componentDidUpdate function. In hooks you can implement something similar with the example shown here: usePrevious.
Using the usePrevious function in the link you can do this:
const prevCount = usePrevious(checkCounter);
// Hook
function usePrevious(value) {
// The ref object is a generic container whose current property is mutable ...
// ... and can hold any value, similar to an instance property on a class
const ref = useRef();
// Store current value in ref
useEffect(() => {
ref.current = value;
}, [value]); // Only re-run if value changes
// Return previous value (happens before update in useEffect above)
return ref.current;
}
useEffect(() => {
if (prevCount === 5 && checkCounter === 1) {
// your code here
}
}, [prevCount, checkCounter])
using the following code to rotate an array of object through a component DOM. The issue is the state never updates and I can't workout why..?
import React, { useState, useEffect } from 'react'
const PremiumUpgrade = (props) => {
const [benefitsActive, setBenefitsActive] = useState(0)
// Benefits Details
const benefits = [
{
title: 'Did they read your message?',
content: 'Get more Control. Find out which users have read your messages!',
color: '#ECBC0D'
},
{
title: 'See who’s checking you out',
content: 'Find your admirers. See who is viewing your profile and when they are viewing you',
color: '#47AF4A'
}
]
// Rotate Benefit Details
useEffect(() => {
setInterval(() => {
console.log(benefits.length)
console.log(benefitsActive)
if (benefitsActive >= benefits.length) {
console.log('................................. reset')
setBenefitsActive(0)
} else {
console.log('................................. increment')
setBenefitsActive(benefitsActive + 1)
}
}, 3000)
}, [])
the output I get looks like the following image. I can see the useState 'setBenefitsActive' is being called but 'benefitsActive' is never updated.
You pass no dependencies to useEffect meaning it will only ever run once, as a result the parameter for setInterval will only ever receive the initial value of benefitsActive (which in this case is 0).
You can modify the existing state by using a function rather than just setting the value i.e.
setBenefitsActive(v => v + 1);
Some code for your benefit!
In your useEffect as #James suggested, add a dependency to the variable that's being updated. Also don't forget to clean up your interval to avoid memory leaks!
// Rotate Benefit Details
useEffect(() => {
let rotationInterval = setInterval(() => {
console.log(benefits.length)
console.log(benefitsActive)
if (benefitsActive >= benefits.length) {
console.log('................................. reset')
setBenefitsActive(0)
} else {
console.log('................................. increment')
setBenefitsActive(benefitsActive + 1)
}
}, 3000)
//Clean up can be done like this
return () => {
clearInterval(rotationInterval);
}
}, [benefitsActive]) // Add dependencies here
Working Sandbox : https://codesandbox.io/s/react-hooks-interval-demo-p1f2n
EDIT
As pointed out by James this can be better achieved by setTimeout with a much cleaner implementation.
// Rotate Benefit Details
useEffect(() => {
let rotationInterval = setTimeout(() => {
console.log(benefits.length)
console.log(benefitsActive)
if (benefitsActive >= benefits.length) {
console.log('................................. reset')
setBenefitsActive(0)
} else {
console.log('................................. increment')
setBenefitsActive(benefitsActive + 1)
}
}, 3000)
}, [benefitsActive]) // Add dependencies here
Here, a sort of interval is created automatically due to the useEffect being called after each setTimeout, creating a closed loop.
If you still want to use interval though the cleanup is mandatory to avoid memory leaks.
When you pass a function to setInterval, you create a closure, which remembers initial value of benefitsActive. One way to get around this is to use a ref:
const benefitsActive = useRef(0);
// Rotate Benefit Details
useEffect(() => {
const id = setInterval(() => {
console.log(benefits.length);
console.log(benefitsActive.current);
if (benefitsActive.current >= benefits.length) {
console.log("................................. reset");
benefitsActive.current = 0;
} else {
console.log("................................. increment");
benefitsActive.current += 1;
}
}, 3000);
return () => clearInterval(id);
}, []);
Demo: https://codesandbox.io/s/delicate-surf-qghl6
I've had the same problem and found a perfect solution on
https://overreacted.io/making-setinterval-declarative-with-react-hooks/
using an own hook
import { useRef, useEffect } from "react";
export function useInterval(callback, delay) {
const savedCallback = useRef();
useEffect(() => {
savedCallback.current = callback;
}, [callback]);
useEffect(() => {
function tick() {
savedCallback.current();
}
if (delay !== null) {
const id = setInterval(tick, delay);
return () => clearInterval(id);
}
}, [delay]);
}
using it like
useInterval(() => {
// Your custom logic here
setCount(count + 1);
}, 1000);
To restrict useEffect from running on the first render we can do:
const isFirstRun = useRef(true);
useEffect (() => {
if (isFirstRun.current) {
isFirstRun.current = false;
return;
}
console.log("Effect was run");
});
According to example here: https://stackoverflow.com/a/53351556/3102993
But what if my component has multiple useEffects, each of which handle a different useState change? I've tried using the isFirstRun.current logic in the other useEffect but since one returns, the other one still runs on the initial render.
Some context:
const Comp = () => {
const [ amount, setAmount ] = useState(props.Item ? Item.Val : 0);
const [ type, setType ] = useState(props.Item ? Item.Type : "Type1");
useEffect(() => {
props.OnAmountChange(amount);
}, [amount]);
useEffect(() => {
props.OnTypeChange(type);
}, [type]);
return {
<>
// Radio button group for selecting Type
// Input field for setting Amount
</>
}
}
The reason I've used separate useEffects for each is because if I do the following, it doesn't update the amount.
useEffect(() => {
if (amount) {
props.OnAmountChange(amount);
} else if (type) {
props.OnTypeChange(type)
}
}, [amount, type]);
As far as I understand, you need to control the execution of useEffect logic on the first mount and consecutive rerenders. You want to skip the first useEffect. Effects run after the render of the components.
So if you are using this solution:
const isFirstRun = useRef(true);
useEffect (() => {
if (isFirstRun.current) {
isFirstRun.current = false;
return;
}
console.log("Effect was run");
});
useEffect (() => {
// second useEffect
if(!isFirstRun) {
console.log("Effect was run");
}
});
So in this case, once isFirstRun ref is set to false, for all the consecutive effects the value of isFirstRun becomes false and hence all will run.
What you can do is, use something like a useMount custom Hook which can tell you whether it is the first render or a consecutive rerender. Here is the example code:
const {useState} = React
function useMounted() {
const [isMounted, setIsMounted] = useState(false)
React.useEffect(() => {
setIsMounted(true)
}, [])
return isMounted
}
function App() {
const [valueFirst, setValueFirst] = useState(0)
const [valueSecond, setValueSecond] = useState(0)
const isMounted = useMounted()
//1st effect which should run whenever valueFirst change except
//first time
React.useEffect(() => {
if (isMounted) {
console.log("valueFirst ran")
}
}, [valueFirst])
//2nd effect which should run whenever valueFirst change except
//first time
React.useEffect(() => {
if (isMounted) {
console.log("valueSecond ran")
}
}, [valueSecond])
return ( <
div >
<
span > {
valueFirst
} < /span> <
button onClick = {
() => {
setValueFirst((c) => c + 1)
}
} >
Trigger valueFirstEffect < /button> <
span > {
valueSecond
} < /span> <
button onClick = {
() => {
setValueSecond((c) => c + 1)
}
} >
Trigger valueSecondEffect < /button>
<
/div>
)
}
ReactDOM.render( < App / > , document.getElementById("root"))
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.8.3/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.8.3/umd/react-dom.production.min.js"></script>
<div id="root"></div>
I hope it helps !!
You can use a single useEffect to do both effects in, you just implemented the logic incorrectly.
Your original attempt:
useEffect(() => {
if (amount) {
props.OnAmountChange(amount);
} else if (type) {
props.OnTypeChange(type)
}
}, [amount, type]);
The issue here is the if/elseif, treat these as independent effects instead:
useEffect(() => {
if (amount !== 0) props.onAmountChange(amount);
if (type !== "Type1") props.onTypeChange(type);
}, [amount, type])
In this method if the value is different than the original value, it will call the on change. This has a bug however in that if the user ever switches the value back to the default it won't work. So I would suggest implementing the entire bit of code like this instead:
const Comp = () => {
const [ amount, setAmount ] = useState(null);
const [ type, setType ] = useState(null);
useEffect(() => {
if (amount !== null) {
props.onAmountChange(amount);
} else {
props.onAmountChange(0);
}
}, [amount]);
useEffect(() => {
if (type !== null) {
props.onTypeChange(type);
} else {
props.onTypeChange("Type1");
}
}, [type]);
return (
<>
// Radio button group for selecting Type
// Input field for setting Amount
</>
)
}
By using null as the initial state, you can delay calling the props methods until the user sets a value in the Radio that changes the states.
If you are using multiple useEffects that check for isFirstRun, make sure only the last one (on bottom) is setting isFirstRun to false. React goes through useEffects in order!
creds to #Dror Bar comment from react-hooks: skip first run in useEffect