Here is my code:
function StockCard(props) {
const [FetchInterval, setFetchInterval] = useState(300000);
const [StockData, setStockData] = useState({});
const [TrendDirection, setTrendDirection] = useState(0);
const [Trend, setTrend] = useState(0);
const FetchData = async () =>{
const resp = await Axios.get(`http://localhost:8080/stock/getquote/${props.API}`)
setStockData(resp.data);
}
const calculateTrendDirection = () => {
if(StockData.lastPrice.currentPrice > StockData.lastPrice.previousClosePrice){
setTrendDirection(1);
} else if (StockData.lastPrice.currentPrice < StockData.lastPrice.previousClosePrice){
setTrendDirection(-1);
} else {
setTrendDirection(0);
}
}
const calculateTrend = () => {
var result = 100 * Math.abs( ( StockData.lastPrice.previousClosePrice - StockData.lastPrice.currentPrice ) / ( (StockData.lastPrice.previousClosePrice + StockData.lastPrice.currentPrice)/2 ) );
setTrend(result.toFixed(2));
}
useEffect(() => {
FetchData();
const interval = setInterval(async () => {
await FetchData();
}, FetchInterval)
return() => clearInterval(interval);
},[FetchInterval]);
useEffect(()=>{
if(StockData.lastPrice){
console.log("Trends calculated", StockData.name);
calculateTrend();
calculateTrendDirection();
}
},[StockData])
return(
<div>
<CryptoCard
currencyName={StockData.lastPrice? StockData.name : "Name"}
currencyPrice={StockData.lastPrice? `$ ${StockData.lastPrice.currentPrice}` : 0}
icon={<img src="https://upload.wikimedia.org/wikipedia/commons/thumb/4/46/Bitcoin.svg/2000px-Bitcoin.svg.png"/>}
currencyShortName={StockData.lastPrice? StockData.symbol : "Symbol"}
trend={StockData.lastPrice? `${Trend} %` : 0}
trendDirection={StockData.lastPrice? TrendDirection : 0}
chartData={[9200, 5720, 8100, 6734, 7054, 7832, 6421, 7383, 8697, 8850]}
/>
</div>
)
}
export default StockCard;
The basic idea is. I have a backend from which I fetch data let's say every minute(this is why i need setInterval) and I have cards which are showing off the data i fetched. I have an expression so it says generic things like "Name" until the data has arrived, then it should re-render with the real data.
But this doesn't happen. It fetches all the data, I can log it out but it doesn't get updated.
And error number 2 is it says that in the useEffects i should include the functions into dependencies.
So for example in the second useEffect where I call the function calculateTrend() and calculateTrendDirection, it says I should include not only the StockData but the two functions too.
I tried #Ozgur Sar 's fix and it worked, so it turned out the problem was "timing" with my api calls
Related
Why "Cards" still doesn't receive the passed value from selectedCountryInfo
I just tried passing await to the variable, still doesn't work. "Cards" still don't receive value.
<----solution: when there are have 2 setStates, should use 2 variables, not use 1 variable.(I guess if there are 3 setStates use 3 variables and so on)
I've been thinking about it for over 12 hours and can't think of a solution.
Because the default value of useState cannot put async/await.
(fetchedCountries is array,selectedCountryInfo is object)
const App = () => {
const [fetchedCountries, setFetchedCountries] = useState([]);
const [selectedCountryInfo, SetSelectedCountryInfo] = useState();
useEffect(() => {
const myCountries = async () => {
const countries = await worldWideCountries();
setFetchedCountries(countries);
SetSelectedCountryInfo(fetchedCountries[0]);
};
myCountries();
}, []);
return (
<div>
<Cards selectedCountryInfo={selectedCountryInfo} />
</div>
);
Solution:(from the 3 lines)
const countries = await worldWideCountries();
setFetchedCountries(countries);
const ww = countries[0];
SetSelectedCountryInfo(ww);
You probably want to use conditional rendering
const App = () => {
const [fetchedCountries, setFetchedCountries] = useState([]);
const [selectedCountryInfo, SetSelectedCountryInfo] = useState();
useEffect(() => {
const myCountries = async () => {
setFetchedCountries(await worldWideCountries());
SetSelectedCountryInfo(fetchedCountries[0]);
};
myCountries();
}, []);
return (
<div>
{ selectedCountryInfo && <Cards selectedCountryInfo={selectedCountryInfo} /> }
</div>
);
}
This should be fairly simple, but I keep getting a weird behaviour from the result.
Basically, I have an array of images:
const images = [img1, img2, img3, img4, img5, img6];
I also have an image index:
const [imageIndex, setImageIndex] = useState(0);
Then I do a little incrementation of the index:
const switchImage = () => {
if (imageIndex === images.length - 1) {
setImageIndex(0);
} else {
setImageIndex(imageIndex + 1);
}
return imageIndex;
}
Then I call this function from a useEffect:
useEffect(() => {
setInterval(() => {
switchImage();
}, 1000);
}, []);
And finally I add the html:
<img src={images[imageIndex]} />
The result is usually it gets stuck on the second image and stops incrementing, so I thought the issue might be with the useEffect and the way the component is rendering.
You need to use the second method signature of the useState setter function which gives you the previous state value to avoid the stale closure captured value.
const root = ReactDOM.createRoot(document.getElementById('root'));
const images = ['1','2','3','4','5','6'];
const Thing =()=>{
const [imageIndex, setImageIndex] = React.useState(0);
React.useEffect(() => {
setInterval(() => {
setImageIndex(prev => (
prev === images.length - 1 ? 0 : prev + 1
));
}, 1000);
},[])
console.log(imageIndex)
return (
<div>
<h1>{images[imageIndex]}</h1>
</div>
);
}
root.render(<Thing />);
See here https://codepen.io/drGreen/pen/JjpmQrV
Also worth seeing this link which is virtually identical.
In your case the useEffect which you have created it is only being triggered once; when the component is loading - that is because you did not define when this logic should be triggered by adding dependencies to the useEffect.
Now, since the component renders once, 'switchImage'()' is only being triggered once, hence, it iterates once, display the img and stops.
Here is some good documentation on useEffect if you would like to read more about it Using the Effect Hook - React
💡Here is a slightly altered solution where we are using the debounce technique for the timer. SOLUTION💡
const root = ReactDOM.createRoot(document.getElementById('root'));
const images = ['💡','😊','😁','😍','🎯','👌'];
const DemoComponent = () =>{
const [imageIndex, setImageIndex] = React.useState(0);
//debounce set default 0.3s
const debounce = (func, timeout = 300) =>{
let timer;
return (...args) => {
clearTimeout(timer);
timer = setTimeout(() => { func.apply(this, args); }, timeout);
};
}
// switch img fn.
const switchImage = () => {
setImageIndex(imageIndex === images.length - 1 ? 0 : imageIndex + 1)
return imageIndex;
}
//debounce switchImage and set timer to 1s
const switchImageDebounce = debounce(() => switchImage(),1000);
//useEffect
React.useEffect(() => {
switchImageDebounce()
}, [imageIndex]);
return (
<div>
<h1>{images[imageIndex]}</h1>
</div>
);
}
root.render();
I have a webpage where I fetch the data with async axios and then make calculations with them.
Here is the code snippet:
const FetchData = async () =>{
console.log("FETCH CALLED");
await Axios.get(`http://localhost:8080/stock/getquote/${props.API}`)
.then(resp => {
setStockData(resp.data);
calculateTrend();
calculateTrendDirection();
})
}
Here, I get the error at calculateTrend() function. My question is, that this .then() should run when the response has arrived, but it seems that it runs before. Because both calculateTrend and calculateTrendDirection works with this fetched data
Edit: The error I am getting is Cannot read property 'previousClosePrice' of undefined. I am sure this exist in the object so mispelling is not a problem
Edit2: I edited my Component according to your solutions and one happens to work, the only thing is that the fetching gets to an infinite loop and fetches multiple times a second. My suspect is the dependencies in useEffect, but I am not sure what to set there.
Here is my full component:
function StockCard(props) {
const [FetchInterval, setFetchInterval] = useState(300000);
const [StockData, setStockData] = useState({});
const [TrendDirection, setTrendDirection] = useState(0);
const [Trend, setTrend] = useState(0);
const FetchData = async () =>{
console.log("FETCH CALLED");
const resp = await Axios.get(`http://localhost:8080/stock/getquote/${props.API}`)
setStockData(resp.data);
}
const calculateTrendDirection = () => {
console.log(StockData.lastPrice);
if(StockData.lastPrice.currentPrice > StockData.lastPrice.previousClosePrice){
setTrendDirection(1);
} else if (StockData.lastPrice.currentPrice < StockData.lastPrice.previousClosePrice){
setTrendDirection(-1);
} else {
setTrendDirection(0);
}
}
const calculateTrend = () => {
console.log(StockData.lastPrice);
var result = 100 * Math.abs( ( StockData.lastPrice.previousClosePrice - StockData.lastPrice.currentPrice ) / ( (StockData.lastPrice.previousClosePrice + StockData.lastPrice.currentPrice)/2 ) );
setTrend(result.toFixed(2));
}
useEffect(() => {
FetchData();
if(StockData.lastPrice){
console.log("LÉTEZIK A LAST PRICE")
calculateTrend();
calculateTrendDirection();
}
const interval = setInterval(() => {
FetchData();
}, FetchInterval)
return() => clearInterval(interval);
},[StockData, FetchData, FetchInterval, calculateTrend, calculateTrendDirection]);
return(
<div>
<CryptoCard
currencyName={StockData.lastPrice? StockData.name : "Name"}
currencyPrice={StockData.lastPrice? `$ ${StockData.lastPrice.currentPrice}` : 0}
icon={<img src="https://upload.wikimedia.org/wikipedia/commons/thumb/4/46/Bitcoin.svg/2000px-Bitcoin.svg.png"/>}
currencyShortName={StockData.lastPrice? StockData.symbol : "Symbol"}
trend={StockData.lastPrice? `${Trend} %` : 0}
trendDirection={StockData.lastPrice? TrendDirection : 0}
chartData={[9200, 5720, 8100, 6734, 7054, 7832, 6421, 7383, 8697, 8850]}
/>
</div>
)
The then block is called only after the promise is fulfilled, so the data is available at that point.
From what I can see, the problem is setStockData tries to set the stockData state variable with the response, but calculateTrend and calculateTrendDirection are called before the state is set because updating state values is batched.
There are several solutions to the problem.
Solution 1:
You can call the two functions after the state is set:
setStockData(resp.data, () => {
calculateTrend();
calculateTrendDirection();
});
Solution 2:
You can use useEffect to call the functions again after the state is updated:
useEffect(() => {
if (stockData) { // or whatever validation needed
calculateTrend();
calculateTrendDirection();
}
}, [stockData]);
Solution 3:
You can pass the parameters to the method:
calculateTrend(resp.data);
calculateTrendDirection(resp.data);
The best option? I think #2, because it also makes sure that the trend and trend direction are re-calculated whenever stock data is updated (from whatever other causes).
I guess in calculateTrend you are using the data which setStockData sets to the state, if that is the case
setState is not happening right after you call the setState, if you want something to execute after correctly update the State then should look at something like this
setStockData(resp.data, () => {
calculateTrend();// this will call once the state gets changed
});
or you could use useEffect
useEffect(() => {
calculateTrend(); // this will call every time when stockData gets changed
}, [stockData])
If you are using stockData inside calculateTrend function and setStockData is an async function, move calculateTrend function to useEffect using stockData as dependency, so every time stockData is updated, calculateTrend and calculateTrendDirection will be called:
useEffect(() => {
const interval = setInterval(() => {
FetchData();
}, FetchInterval);
return() => clearInterval(interval);
}, [FetchInterval]);
useEffect(() => {
if(StockData.lastPrice){
console.log("LÉTEZIK A LAST PRICE")
calculateTrend();
calculateTrendDirection();
}
}, [StockData]);
const FetchData = async () =>{
console.log("FETCH CALLED");
const res = await Axios.get(`http://localhost:8080/stock/getquote/${props.API}`);
setStockData(resp.data);
}
I am struggling due to waring from eslint.
Below is sample code and once I run the below code, I get the waringing from eslint.
React Hook useEffect has a missing dependency: 'maxId'. Either include it or remove the dependency array.
How can I remove the warining?
I want to make the process to call the loadMapData function only when pageNo and StartDate are changed.
Sample Code;
import React, { useState, useEffect, useCallback } from "react";
const VehicleHistory = (props) => {
//console.log("VehicleHistory");
const pageSize = 10;
const [mapData, setMapData] = useState();
const [pageNo, setpageNo] = useState(1);
const [startDate, setstartDate] = useState(100);
const [maxId, setmaxId] = useState(0);
useEffect(() => {
console.log("useEffect.pageNo chainging====");
const loadMapData = async () => {
console.log('call loadMapData====');
try {
//Api call to get list data
//No meaning. Just for testing
const _pageNo = pageNo;
const _pageSize = pageSize
const _maxId = maxId;
setMapData('test'+_pageNo + _pageSize+_maxId);
setmaxId(_pageNo + _pageSize);
} catch (err) {
console.log("err", err);
}
}
loadMapData();
}, [pageNo]);
useEffect(() => {
console.log("useEffect.startDate chainging====");
setMapData(null);
setpageNo(1);
}, [startDate]);
return (
<div>
<button onClick={e => setpageNo(p => p + 1)}>Change page</button>
<button onClick={e => setstartDate(s => s + 1)}>Change date</button>
<br />pageNo : {pageNo}
<br />startdate : {startDate}
<br />mapdata : {mapData}
</div>
);
};
export default VehicleHistory;
Issue is here in this code. Basically inside useEffect you are expecting maxId. you need to understand how useEffect work. useEffect required array of dependency which ensure it will run whenever these value changes. So in your case maxId is changing. And useEffect is not sure what to that's why eslint giving error.
useEffect(() => {
console.log("useEffect.pageNo chainging====");
const loadMapData = async () => {
console.log('call loadMapData====');
try {
//Api call to get list data
//No meaning. Just for testing
const _pageNo = pageNo;
const _pageSize = pageSize
const _maxId = maxId; <- Issue is here
setMapData('test'+_pageNo + _pageSize+_maxId);
setmaxId(_pageNo + _pageSize);
} catch (err) {
console.log("err", err);
}
}
loadMapData();
}, [pageNo]);
Solution:
useEffect(() => {
...code
},[pageNo,maxId]) <- add maxId in dependency array
I've got the following code:
export default function App() {
const [lastMessageId, setLastMessageId] = useState(0);
const [messages, setMessages] = useState([]);
const addMessage = (body, type) => {
const newMessage = {
id: lastMessageId + 1,
type: type,
body: body,
};
setLastMessageId(newMessage.id)
setMessages([...messages, newMessage]);
console.log("point 1", messages);
return newMessage.id;
}
// remove a message with id
const removeMessage = (id) => {
const filter = messages.filter(m => m.id !== id);
console.log("point 2", filter);
setMessages(filter);
}
// add a new message and then remove it after some seconds
const addMessageWithTimer = (body, type="is-primary", seconds=5) => {
const id = addMessage(body, type);
setTimeout(() => removeMessage(id), seconds*1000);
};
return (
...
);
}
I would like to know why after I setMessages at point 1, when I do console log it doesn't appear to be updated. This turns into a weird behaviour when I call addMessageWithTimer because when it calls removeMessage then it doesn't remove correctly the messages that I expect.
Could you please explain me how to do it?
Just like setState in class-components, the update functions of useState don't immediately update state, they schedule state to be updated.
When you call setMessages it causes react to schedule a new render of App which will execute the App function again, and useState will return the new value of messages.
And if you think about it from a pure JS perspective, messages can't change: it's just a local variable, (a const one, even). Calling a non-local function can't cause a local variable's value to change, JS just doesn't work that way.
#Retsam is correct in his explanation.
I think you would get an issue if you don't use setTimeout in addMessageWithTimer. Isn't it? But for now, it is correct.
If you don't want to give a timer of 5 seconds and still want to keep it running correctly, then give a timer of 0 seconds. It would still work okay.
what weird behavior your seeing?
when I tried your code, I'm able to remove the added message after 5 sec.
import React, { useState } from "react";
import "./styles.css";
export default function App() {
let bodyText = "";
const [lastMessageId, setLastMessageId] = useState(0);
const [messages, setMessages] = useState([]);
const addMessage = (body, type) => {
if (body === "") return;
const newMessage = {
id: lastMessageId + 1,
type: type,
body: body
};
setLastMessageId(newMessage.id);
setMessages([...messages, newMessage]);
bodyText = "";
return newMessage.id;
};
// remove a message with id
const removeMessage = (id) => {
const filter = messages.filter((m) => m.id !== id);
console.log("point 2", filter);
setMessages(filter);
};
// add a new message and then remove it after some seconds
const addMessageWithTimer = (body, type = "is-primary", seconds = 5) => {
const id = addMessage(body, type);
setTimeout(() => removeMessage(id), seconds * 1000);
};
console.log("point 1", messages);
return (
<div className="App">
<h1>Hello CodeSandbox</h1>
<h2>Start editing to see some magic happen!</h2>
<input onChange={(e) => (bodyText = e.target.value)} />
<button onClick={(e) => addMessage(bodyText, "is-primary")}>
Add messsage
</button>
<button onClick={(e) => addMessageWithTimer(bodyText, "is-primary", 5)}>
Add temp messsage
</button>
{messages.map((message, id) => {
return (
<div key={id}>
<p>
{message.id} {message.body}
</p>
</div>
);
})}
</div>
);
}
#Retsam was very useful with his answer as I was able to understand the problem and find a proper solution.
here is the solution that I've found:
export default function App() {
const [lastMessageId, setLastMessageId] = useState(0);
const [messages, setMessages] = useState([]);
const addMessage = (body, type="is-primary") => {
const newMessage = {
id: lastMessageId + 1,
type: type,
body: body
};
setLastMessageId(newMessage.id)
setMessages([...messages, newMessage]);
return newMessage.id;
}
// delete messages after 5 seconds
useEffect(() => {
if (!messages.length) return;
const timer = setTimeout(() => {
const remainingMessages = [...messages];
remainingMessages.shift();
setMessages(remainingMessages);
}, 5*1000);
return () => clearTimeout(timer);
}, [messages]);
return (
...
);
}