I have created a functional component called Timer. I want to run a Timer for 3 seconds followed by a Timer for 6 seconds. However, the second timer stops as soon as it starts.
I think the problem is that the second Timer is using the state value from the first Timer. I'm not sure why it does that. I assume that the second Timer is a new instance so it shouldn't have any link with the first Timer.
Here's my code:
import React, { useEffect, useState } from 'react';
function App() {
const [timer1Up, setTimer1Up] = useState(false);
const [timer2Up, setTimer2Up] = useState(false);
if(!timer1Up) {
return <Timer duration={3} setTimeUp={setTimer1Up}/>
}
if(timer1Up && !timer2Up) {
return <Timer duration={6} setTimeUp={setTimer2Up}/>
}
if(timer1Up && timer2Up) {
return <>Out of all your time buddy!!</>
}
return <>I have no purpose</>;
}
interface TimerProps {
duration: number;
setTimeUp: any;
}
const Timer = (props: TimerProps) => {
const [timeLeft, setTimeLeft] = useState(props.duration);
useEffect(() => {
setTimeout(() => {
setTimeLeft(timeLeft - 1);
}, 1000);
if(timeLeft === 0) {
props.setTimeUp(true);
}
});
return <>{timeLeft} s</>
}
export default App;
if(!timer1Up) {
return <Timer duration={3} setTimeUp={setTimer1Up}/>
}
if(timer1Up && !timer2Up) {
return <Timer duration={6} setTimeUp={setTimer2Up}/>
}
The main way react uses to tell whether it needs to mount a new component or reuse an existing one is by the component's type. The first time this renders, you return a <Timer>, so react mounts a new Timer component, which then starts doing a countdown. Once the first countdown is done you render again and you also return a <Timer>. So as far as react can tell, the only thing that changed was the props on that timer. React keeps the same component mounted, with the same state.
So there are two options 1) force it to remount, or 2) let Timer reset if its props change
To force it to remount, you will need to use keys to make it clear to react that these are different elements. That way it will unmount the old timer and mount a new one, and that new one can have its own state that it counts down
if(!timer1Up) {
return <Timer key="first" duration={3} setTimeUp={setTimer1Up}/>
}
if(timer1Up && !timer2Up) {
return <Timer key="second" duration={6} setTimeUp={setTimer2Up}/>
}
To make it work with changing props, you'll need to add logic to reset the countdown. You'll have to decide what conditions should reset the countdown, but one option is that any time the duration changes, you start over:
const Timer = (props: TimerProps) => {
const [timeLeft, setTimeLeft] = useState(props.duration);
useEffect(() => {
setTimeLeft(props.duration);
const intervalId = setInterval(() => {
setTimeLeft(prev => {
const next = prev -1;
if (next === 0) {
clearInterval(intervalId);
// Need to slightly delay calling props.setTimeUp, because setting
// state in a different component while in the middle of setting
// state here can cause an error
setTimeout(() => props.setTimeUp(true));
}
return next;
});
}, 1000);
return () => { clearInterval(intervalId); }
}, [props.duration]); // <---- dependency array to reset when the duration changes
return <>{timeLeft} s</>
}
For more information on how react decides to mount/unmount components, see this page on reconciliation.
Related
The following code demonstrates a react functional component that has a single state variable named time. It has a button click to start which fires a function named updateTimer. This meant to move the timer from 0 to 1 to 2 to 3 and so on.
function timer() {
const [time, updateTime] = useState(0);
function updateTimer() {
setInterval(() => {
updateTime(time + 1)
},1000)
}
}
return (
<>
<span>{time} seconds</span>
<button onClick={updateTimer}>Click To Start</button>
</>
)
But what happens is that the timer stops after 1. Apparently, the value of time does not get updated. Could someone please explain this?
To update the state depending on the previous state use:
updateTime((prevTime) => prevTime + 1)
Because updateTime updates the value of time in the next render of the component, the time known to the setInterval callback is not updated and remained the initial value 0, and resets to 1 at every interval.
In a useEffect run the setter updateTime based on previous value to correct the counting, also cleanup and recreate the interval as needed when the counting starts or stops.
For a basic example, the following useEffect starts an interval when updating is set true by the button. The return runs when
updating changes or when the component unmounted for cleaning up the interval, before a new one can be recreated.
useEffect(() => {
if (!updating) return;
const count = setInterval(() => {
updateTime((prev) => prev + 1);
}, 1000);
return () => {
clearInterval(count);
};
}, [updating]);
updating is added to the dependencies array so that useEffect listens to the changes of this state, and creates a new interval if it is true.
The setter updateTime does not change and it sets time based on the previous value internally, so updateTime and time do not need to be included in the dependencies array.
Example in full snippet:
const { useState, useEffect, Fragment } = React;
function Timer() {
const [time, updateTime] = useState(0);
const [updating, setUpdating] = useState(false);
useEffect(() => {
if (!updating) return;
const count = setInterval(() => {
updateTime((prev) => prev + 1);
}, 1000);
return () => {
clearInterval(count);
};
}, [updating]);
return (
<Fragment>
<p>{time} seconds</p>
<button onClick={() => setUpdating((prev) => !prev)}>{`Click To ${
updating ? "Stop" : "Start"
}`}</button>
</Fragment>
);
}
const App = () => {
return (
<div className="App">
<Timer />
</div>
);
};
ReactDOM.render(<App />, document.querySelector("#root"));
.App {
font-size: x-large;
}
button {
padding: 9px;
}
<div id="root"></div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/18.1.0/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/18.1.0/umd/react-dom.production.min.js"></script>
I am trying to capture the no of clicks by the user.
Which i wish to send to an api every 15 min,
I am useing setinterval inside useEffect to achive this, but the problem is even though the state is changing outside but not inside setinterval. setinterval is only giving the initial default value.
here is the code -
const Agent = (props: RouteComponentProps) => {
const [clicks, setClicks] = useState(0);
const handleOnIdle = () => {
console.log("user is idle");
console.log("last active", new Date(getLastActiveTime()));
console.log("total idle time: ", getTotalIdleTime() / 1000);
};
const handleOnActive = () => {
console.log("user is active");
console.log("time remaining", getRemainingTime());
};
const handleOnAction = () => {
console.log("user did something", clicks);
setClicks(clicks + 1);
};
const {
getRemainingTime,
getLastActiveTime,
getTotalIdleTime,
} = useIdleTimer({
timeout: 10000,
onIdle: handleOnIdle,
onActive: handleOnActive,
onAction: handleOnAction,
debounce: 500,
});
useEffect(() => {
let timer = setInterval(
() => alert(`user clicked ${clicks} times`),
1000 * 30
);
return () => {
clearInterval(timer);
setClicks(0);
};
}, []);
return (
<AgentLayout>
<div className="dashboard-wrapper py-3">
<Switch>
<Redirect
exact
from={`${props.match.url}/`}
to={`${props.match.url}/home`}
/>
<Route path={`${props.match.url}/home`} component={Home} />
<Route
path={`${props.match.url}/lead-details`}
component={leadDetails}
/>
<Route
path={`${props.match.url}/fill-details`}
component={FillDetails}
/>
<Route
path={`${props.match.url}/my-desktime`}
component={MyDesktime}
/>
<Redirect to="/error" />
</Switch>
</div>
</AgentLayout>
the alert is giving user clicked 0 times
The problem is that only the first version of clicks is used by the timer function, because it closes over the version as of the first time your component function is called. When you pass an empty dependency array to useEffect, the useEffect callback is only called once, the first time the component function is called (when mounting the component).
You can fix that by having the timer function use the setClicks method instead:
useEffect(() => {
let timer = setInterval(
() => {
setClicks(currentClicks => { // ***
alert(`user clicked ${currentClicks} times`); // ***
return currentClicks; // ***
}); // ***
},
1000 * 30
);
return () => {
clearInterval(timer);
// setClicks(0); // <=== Don't do this, the component is unmounting
};
}, []);
Now, the timer calls the setClicks using the callback form, which means it receives the current value of clicks. Because it returns that same value, it doesn't update the state of the component.
It's also possible to solve this by adding clicks as a dependency to the useEffect, but it's a bit complicated. The naive way would be just to do this:
// The naive way
useEffect(() => {
let timer = setInterval(
() => {
alert(`user clicked ${clicks} times`);
},
1000 * 30
);
return () => {
clearInterval(timer);
// setClicks(0); // <=== Don't do this, the user's click count would get reset every time
};
}, [clicks]);
// ^^^^^^−−−−−−−−−−−−− ***
That will mostly work, but it will restart the timer every time clicks changes, even if that means that instead of waiting 30 seconds, it waits 45 (because clicks changed after 15 seconds, which cancelled the previous interval and started it again). That probably wouldn't matter for a really short interval, but for a 30 second one it seems less than ideal. Doing it this way without messing up the timing of the interval requires that you remember when the next timer callback should have happened and adjusting the duration of the initial delay to match, which gets fairly complicated.
I didn't notice earlier, but any time you're updating state based on existing state, I recommend using the callback form. So your
const handleOnAction = () => {
setClicks(clicks => clicks + 1); // Note the function callback
};
Issues
You've a stale enclosure of the clicks state, closed over from the initial render cycle when the mounting effect ran and started the interval.
Your click updater should use a functional update to update the clicks count from the previous state. This covers if the user is somehow able to click faster then the react component lifecycle and enqueue more than one clicks update in a render cycle.
T.J.'s answer is good, but I consider the useState updater function to be a pure function and the alert(`user clicked ${currentClicks} times`); in the middle of it is a side-effect and (IMHO) should be avoided.
Solution
Update handleOnAction to use a functional state update.
const handleOnAction = () => {
console.log("user did something", clicks);
setClicks(clicks => clicks + 1);
};
I suggest using a React ref and additional useEffect to update it, to hold a cached copy of the clicks state for the interval callback to reference.
const clicksRef = useRef();
useEffect(() => {
clicksRef.current = clicks; // update clicks ref when clicks updates
}, [clicks]);
useEffect(() => {
const timer = setInterval(
() => alert(`user clicked ${clicksRef.current} times`), // use clicks ref instead
1000 * 30
);
return () => {
clearInterval(timer);
// TJ already covered removing this extra state update
};
}, []);
I'm working on the simple timer app in the React. Below is the code of what I have.
import React from "react"
const timer = (props) => {
let time = 25;
let processStatus = props.timerProcessStatus; // it comes as true
if(processStatus === true) {
setTimeout(() => {
console.log(proccessStatus);
countDown();
}, 500)
}
function countDown(){
time=time-1;
console.log(time);
}
return (
<div>
<p id={props.statusId}>{props.timerStatus}</p>
<p id={props.timerStatusId}>{time}:00</p>
</div>
)
}
export default timer;
And here is the snapshot of what I get in the browser
As it shows, the time variable changed to 24 (although I would expect it to decrease to 23 second time), it doesn't re-renders in the paragraph, where the content is {time}:00
Incrementing a local variable won't cause a re-render of your component.
You need to put time in the state of your component. Updating the state will cause a re-render of the component which will then update the value of time in the DOM.
import React, {useState} from "react"
const timer = (props) => {
const [time, setTime] = useState(25); // local state
...
function countDown(){
setTime(prevTime => prevTime + 1); // update the state
}
...
}
Every time countDown function will be called, it will update the state, causing a re-render of the component.
I suggest you to read React - State and Lifecycle to understand why you need time as a state of the component.
use the following code for the timer .
import React,{UseEffect,UseState} from 'react';
const timer=(props)=>{
const [time, setTime] = useState(25);
UseEffect(()=>{
let processStatus = props.timerProcessStatus;
// it comes as true
if(processStatus === true) { setTimeout(() => { console.log(proccessStatus); countDown(); }, 500) }
}, [])
function countDown(){
setTime(time--);
}
// other code
setInterval is the method to be used to run code/function in specific interval..
any async task should be run in useEffect
function App(){
const [time,setTime]=React.useState(25)
let processStatus = true; // it comes as true
function countDown() {
// time = time - 1;
setTime(prevTime=>prevTime-1)
// console.log(time);
}
let timer;
React.useEffect(() => {
if (processStatus === true) {
timer = setInterval(() => {
countDown();
}, 500);
}
return ()=>{
clearInterval(timer)
}
}, []);
return (
<div className="App">
<h1>Hello CodeSandbox-{time}</h1>
<h2>Start editing to see some magic happen!</h2>
</div>
);
}
ReactDOM.render(<App/>,document.getElementById("root"))
<script src= "https://unpkg.com/react#16/umd/react.production.min.js"></script>
<script src= "https://unpkg.com/react-dom#16/umd/react-dom.production.min.js"></script>
<script src="https://unpkg.com/babel-standalone#6.15.0/babel.min.js"></script>
<div id="root"></div>
My guess is that it tries to create the time variable each time
so I would suggest to put the time variable in its parent component then just use
function countDown(){
let newTime = time;
props.setTime(newTime - 1);
console.log(newTime - 1);
}
Im having a lot of trouble with this and i have tried various things. I want to call a function every second after i have clicked a start button and then have it paused after i click a stop button. I keep getting weird behaviour that i cant explain.
How can i do this in react without classes?
somethings i have treid:
const simulation = () => {
if (!running) {
console.log('hit');
return
} else {
// console.log(grid);
console.log('hey');
setTimeout(simulation, 1000)
}
}
and
enter setInterval(() => {
let newGrid = [...grid]
for (let i = 0; i < numRow; i++) {
for (let k = 0; k < numCol; k++) {
let n = 0;
}
}
console.log(grid);
}, 5000)
I have tried a lot more, In some cases it would update the state should i have added to it but not updated it after i reset the state.
How can i call a function to run every one second with updated values of state * Note the function that i want to run will update the state
You may do the following:
keep track of the current counter value along with the counter on/off state in your component state;
employ useEffect() hook to be called upon turning counter on/off or incrementing that;
within useEffect() body you may call the function, incrementing count by one (if ticking is truthy, hence timer is on) with delayed execution (using setTimeout());
once count variable is changed in the state, useEffect() gets called once again in a loop;
in order to clean up the timer upon component dismantle, you should return a callback, clearing the timer from useEffect()
const { useState, useEffect } = React,
{ render } = ReactDOM,
rootNode = document.getElementById('root')
const App = () => {
const [ticking, setTicking] = useState(true),
[count, setCount] = useState(0)
useEffect(() => {
const timer = setTimeout(() => ticking && setCount(count+1), 1e3)
return () => clearTimeout(timer)
}, [count, ticking])
return (
<div>
<div>{count}</div>
<button onClick={() => setTicking(false)}>pause</button>
<button onClick={() => setTicking(true)}>resume</button>
</div>
)
}
render (
<App />,
rootNode
)
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.12.0/umd/react.production.min.js"></script><script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.11.0/umd/react-dom.production.min.js"></script><div id="root"></div>
Late reply but maybe interesting for some people.
Look at npm package cron. In this case every 15min As easy as:
const [job] = useState(new cron.CronJob("0 */15 * * * *",async ()=>{
await updateRiderCoords();
}));
useEffect(() => {
job.start();
}, []);
I have an array with 3 elements. I want to loop through it such that after 3 seconds the next element of array is rendered in place of the previous one and if last element is rendered then it should restart again. It's like after 3 seconds I want to display the next element in place of previous one as like looping through the array but showing one element at a time. I have tried the following code for it.
import React, { useEffect, useState } from 'react';
import './text.css';
const Text = () => {
var work = ["fighting", "learning", "qwerty"];
const [seconds, setSeconds] = useState(0);
useEffect(() => {
const interval = setInterval(() => {
if(seconds===2) setSeconds(seconds => seconds = 0);
else setSeconds(seconds => seconds + 1);
console.log(seconds);
}, 3000);
}, []);
return (
<div>
<h1>{work[seconds]}</h1>
</div>
);
}
export default Text;
It is successfully rendering elements one after another but can't render anything after the last element. Also on console the value of seconds is always showing 0.
The issue is that the initial state value is enclosed in the scope of the callback and never updates the state value in the outer scope, but defining the callback outside allows the state to update. Also, increment an index value instead and take the modulus of the array length to always get a valid index.
import React, { useEffect, useState } from "react";
const work = ["fighting", "learning", "qwerty"];
export default function App() {
const [index, setIndex] = useState(0);
useEffect(() => {
const tick = () => setIndex(i => i + 1);
const id = setInterval(tick, 3000);
return () => clearInterval(id);
}, []);
return (
<div>
<h1>{work[index % work.length]}</h1>
</div>
);
}
You were not getting the updated second value inside the setInterval.
Also, clearInterval in useEffect.
Working demo
Refactored code
useEffect(() => {
const interval = setInterval(() => {
setSeconds(second => (second === 2 ? 0 : second + 1));
}, 3000);
return () => clearInterval(interval)
}, []);
Update:
The console.log inside setInterval's callback will always be 0 because the seconds inside the setInterval's callback is the value taken when the callback was registered with setInterval.
To see up-to-date values of second, use another useEffect with seconds as dependency.
useEffect(() => {
console.log("seconds", seconds);
}, [seconds]);