I am new to React and I am trying to build a hangman game.
At the moment I am using a hardcoded list of words that the program can choose from. So far everything worked great, but now I am trying to reset the game and the react component that should rerender upon one click only re-renders after two clicks on the reset button and I don't know why
these are the states that I am using :
function App() {
const [numberInList, setNumberInList] = useState(0)
const randomWordsList = ["comfort", "calm", "relax", "coffee", "cozy"];
const [generatedWord, setGeneratedWord] = useState(
randomWordsList[numberInList]
);
const [generatedWordLetters, setGeneratedWordLetters] = useState(
randomWordsList[numberInList].split("").map((letter) => {
return { letter: letter.toUpperCase(), matched: false };
})
);
function resetGame(){
setNumberInList(prev => prev + 1)
setGeneratedWord(randomWordsList[numberInList])
setGeneratedWordLetters(
generatedWord.split("").map((letter) => {
return { letter: letter.toUpperCase(), matched: false };
})
);
setFalseTries(0)
}
this is the reset function I am using
within teh function every state gets updated correctly apart from the generatedWordLetters state, which only gets updated upon clicking the reset button two times.
I can't seem to solve this problem on my own, so any help is appreciated!
Please check useEffect on React. You can use boolean flag as state, put the useEffect parameters like below
React.useEffect(() => {
// here your code works
},[flag])
flag is your boolean state when it changes on reset function, your component re render
Related
Can anyone tell me why at button click, the value outputted to the console is always one unit smaller than displayed on the screen?
The values are not in sync as expected.
Example below in React
In Child:
import React, {useState } from "react";
export const ChildComp = ({getNumProps}) => {
const [num, setNum] = useState(0);
const onPlusClick = () => {
if (num< 12) {
setNum(num + 1);// num does not increase immediately after this line, except when focus reenters here on second method call
}
getNumProps(num);
}
return(
<div>
<button onClick={onPlusClick}>
Click to increment
</button>
{num}
</div>
);
}
In parent
import { ChildComp } from "./ChildComp"
export const ParentComp = () => {
const getNum= (num) => {
console.log(num);
}
return (<ChildComp getNumProps={getNum}/>)
}
The page initially shows 0
When I click once the number increments to 1, but console displays 0
When I click once the number increments to 2, but console displays 1
I should see in the console the same as the page display
Appreciate if you can leave a commen on how the question can be improved.
This is a child to parent communication example. Also, any objections about standards used, please let me know.
Thanks.
Update: I notice the values would be in sync if
instead of getNumProps(num);
I did getNumProps(num + 1); but that doesn't change the fact that previously on this line
setNum(num + 1);, as already pointed out in the comment, num does not increase immediately after this line, except when focus reenters here on second method call. Not sure why.
The prop function getNumProps is a side effect, and should be put into a hook, instead of inside of that onPlusClick function.
Instead, do this:
useEffect(() => {
getNumProp(num);
}, [num]);
Alternatively, to avoid the error: "React Hook useEffect has a missing dependency: 'getNumProps'. See this doc on using the useCallback hook
const callback = useCallback(() => {
getNumProp(num);
}, [num]);
function onPlusClick(...) {
...
callback();
}
The change to the state of num will cause a re-render of the child component, not the parent.
In a component when an input is provided it dispatches the input to a reducer
const changeSearchTerm = (e) => {
setSearchTerm(e.target.value)
dispatch(userActions.searchByName(searchTerm));
}
Then the reducer takes that value and tries to filter the array based on that input
searchByName: (state, action) => {
state.search = action.payload;
let newArray = state.users.filter((user) =>
user.name.toLowerCase().includes(state.search.toLowerCase())
);
state.users = newArray;
},
Then this whole array is displayed in one of the other components. The search bar works to some extent:
When you start typing into the search bar it only starts to work after second input. In console I have noticed that if you type "Timmothy" it will only register "Timmoth" in the state.
Additionaly, if I delete text from the input, the state of the array doesn't update and stays the same even though the input value changes.
So what happens currently is if you start typing in the search bar, it updates the array, but always only registers second to last keystroke. Additionally, if you delete input from the search bar, it doesn't register. The value changes, but the array stays with only few items left.
I have tried to not use the additional variable to store the state and do it like this
state.users.filter((user) =>
user.name.toLowerCase().includes(state.search.toLowerCase())
But then absolutely nothing happens. Would appreciate if someone could tell me what I'm missing here
EDIT
This is the component that receives that input
<input onChange={changeSearchTerm} type="text" value={searchTerm}></input>
And the searchTerm value is saved in useState - const [searchTerm, setSearchTerm] = useState("");
From what I can tell, it only works after the second input because of this block:
const changeSearchTerm = (e) => {
setSearchTerm(e.target.value)
dispatch(userActions.searchByName(searchTerm));
}
State setters like setSearchTerm are actually asynchronous. This means that after you call setSearchTerm, on the next line the value of searchTerm is still the old value.
You can instead do one of the following:
const changeSearchTerm = (e) => {
setSearchTerm(e.target.value)
dispatch(userActions.searchByName(e.target.value));
}
const changeSearchTerm = (e) => {
setSearchTerm(e.target.value, () => {
// This callback runs only after state has changed
dispatch(userActions.searchByName(searchTerm));
});
}
Edit: Sorry I missed that you used useState/functional. You can use useEffect:
const changeSearchTerm = (e) => {
setSearchTerm(e.target.value);
}
useEffect(() => {
if (searchTerm.length > 0) {
dispatch(userActions.searchByName(searchTerm));
}
}, [searchTerm]);
This way your dispatch will correctly run whenever searchTerm's value changes for sure.
https://reactjs.org/docs/react-component.html#setstate
I've tried almost every solution similar to my problem, yet none is working. I have a simple state and changing the value of this state in a function as like below, handleOnClick is calling in a button's onClick event. I'm also using Router(if it's change something);
import { useState} from "react"
import { BrowserRouter as Router, Route, Link, useHistory} from "react-router-dom";
const Buton = () => {
let x = "";
const [lowerState, setLower] = useState("")
const history = useHistory();
const handleOnClick = () => {
x = document.getElementById("my_input").value.toLowerCase();
setLower(x)
console.log(x) //this prints the current value
console.log(lowerState) //this DOES NOT prints the current value, but
// when I put another text into the input and click
// to button, it prints the first value I put here
history.push('/test', {params : lowerState})
};
.
.
.
return (...)
}
export default Buton
Now x is a value that returns from an input HTML element. When I set this value as a state and console log, it doesn't print the value first, when I put something in input again, then it prints the first value. So it's like it's coming 1 step behind.
I've used useEffect() , I did put a second parameter to setLower as console.log(lowerState) and other things on the internet that people suggested, but none is working. Every time, the state is coming 1 step behind. How can I make this state changes immediately?
If you want to use the value of an input in a user event function, the best way (and least buggy) is to bind your input value to local state and then just reference that state in your callback function.
Please try to avoid imperatively pulling values from the DOM using getElementById etc. Here's what I mean:
const [value, setValue] = useState('');
// This will keep everything updated until you need to use it
handleChange(event) {
setValue(event.target.value);
}
// Then just grab whatever is in local state
handleClick() {
history.push('/test', {params : value});
}
return (
<input value={value} onChange={handleChange} />
// Your button is here too
)
This is because when you call setLower(x) it is not an async call. So it doesn't wait. That's why you get the 1 step before value in your state right after setting the value.
Official doc - https://reactjs.org/docs/state-and-lifecycle.html#state-updates-may-be-asynchronous
When you call setLower(x), it doesn't immediately update the lowerState. The new value will be available the next time it renders. Because of that the console.log(x) "works" (since it uses the new value that you gain as a parameter) but console.log(lowerState) uses the old value that hasn't updated to the state yet at that point.
If you want history.push('/test', {params : lowerState}) to work, then you need to use the x there instead of lowerState. Or call it within a useEffect with the lowerState and having lowerState as a dependency parameter to the hook.
This is expected behaviour since React is updating state in a batch
Which mean that the state only gets an update after an eventHandler/function is finished
If you want to do some condition, wrap your logic inside a useEffect
useEffect(() => {
if (lowerState === "your-condition-value") {
history.push("/test", { params: lowerState });
}
}, [lowerState]);
Or in your case, just use the variable directly:
const handleOnClick = () => {
x = document.getElementById("my_input").value.toLowerCase();
history.push("/test", { params: x });
};
You should not worry about that since your app still working as expected
So i would like to suggest that use useRef if need for reference only object which may not causing rerendering. also using let x= "" is not correct, you should write code immutable way
const Buton = () => {
const lowerCaseRef = useRef("")
const history = useHistory();
const handleOnClick = () => {
lowerCaseRef.current =
document.querySelector("#my_input").value.toLowerCase();
console.log(lowerCaseRef.current) //this DOES NOT prints the current value, but
// when I put another text into the input and click
// to button, it prints the first value I put here
history.push('/test', {params : lowerCaseRef.current})
};
return (...)
}
I am using useEffect in react to listen to redux(easy-peasy) state change, but I want to listen to 1st value change only.
Because when my page loads the state has a default value and then API call is made and hence data changes but the API is a polling API, hence it keeps getting the data again and again in a short interval of time. But one of my requirement is to listen only to the 1st API data.
This is what I tried:
1st Approach with empty dependency
useEffect(() => {
// my code
},[])
In this case, I get the default value of my state and not the 1st API response.
2nd Approach with state property in the dependency
useEffect(() => {
// my code
},[myState])
In this case, I keep getting the updated response from the API
both of these approaches didn't work for me. So please suggest a better solution.
You can do so using a ref variable and comparing the state with initial state (which could be null, undefined, empty object depending on your implementation):
const hasRun = useRef(false)
useEffect(() => {
if (!hasRun.current && myState !== initialState) {
hasRun.current = true
// run my code
}
},[myState])
A ref variable won't participate in re-rendering.
What I usually do with this is to have a "previous" state.
You can use this hook for to do that one:
const usePrevious(value) {
const ref = useRef();
useEffect(() => {
ref.current = value;
}, [value]); // only re-run if value changes
// return previous value (happens before update in useEffect)
return ref.current;
}
You can then do:
// I usually create a distinct initial state
const [var, setVar] = useState(null);
const prevVar = usePrevious(var);
useEffect(() => {
if (var !== prevVar && var !== null) {
// logic here
}
}, [prevVar, var]);
Yers you can simplify this by not using the usePrevious hook, but the hook is quite handy and can be used to check the previous value and the current one.
This takes place in a functional component:
import {useEffect} from 'react';
let [clickedOnPiece, setClickedOnPiece] = useState(false);
let [testRender, setTestRender] = useState(false);
useEffect(() => {
testRenderFunction();
}, [])
function testRenderFunction() {
let el = <div onClick={onClickHandler}>Click me</div>;
setTestRender(el);
}
function onClickHandler() {
if (clickedOnPiece) {
console.log("already clicked")
return
}
console.log(clickedOnPiece); //returns false the 1st & 2nd time.
setClickedOnPiece("clicked");
}
return (
<>
{testRender}
</>
)
When I click on div for the first time, I wait until setClickedOnPiece("clicked") successfully updates clickedOnPiece to "clicked". (I check this with React Developer Tools).
When I click div the 2nd time, it doesn't log the new change in state. It still logs clickedOnPiece as false. Why is this?
Okey this problem is because useState is asyncronus. u can read more about this useState set method not reflecting change immediately.
I think the solution is add useEffect like this.
useEffect( () => {
console.log(clickOnPiece);
}
, [clickOnPiece])
If you want to toggle the state, you could do something like this:
let [clickedOnPiece, setClickedOnPiece] = useState(false);
const onClickHandler = () => {
// set the value of clickedOnPiece to the opposite of what it was
// i.e. if it was 'true', set it to 'false'.
setClickedOnPiece(!clickedOnPiece);
console.log(clickedOnPiece);
}
// call the onClickHandler on click
<div onClick={()=>onClickHandler()}>Click me</div>
Looks like you are toggling
let [clickedOnPiece, setClickedOnPiece] = useState(false);
const onClickHandler = () => {
console.log(clickedOnPiece);
setClickedOnPiece(!clickedOnPiece);
}
console.log(clickedOnPiece);
<div onClick={onClickHandler}>Click me</div>
After setting state, don't console immediately because state is an asynchronous.
onClickHandler references the old, previous variable, clickedOnPiece. I believe this is because onClickHandler is not defined in the return statement part of the functional component which would have allowed it a new onClickHandler body to be created each time. Instead, we have the old onClickHandler continually referencing the old clickedOnPiece.
This problem is known as 'stale closures' - a concept I found discussed well at the bottom of this article