'Implementing a countdown timer in React with Hooks
Im trying to render a count down timer on screen with react hooks, but I'm not sure the best way to render it.
I know i'm supposed to use the useEffect to compare current state to previous state, but I don't think I'm doing it correctly.
I would appreciate the help!
I've tried a couple of different ways, none of them work, like setting state whenever whenever it updates, but it just ends up flickering like crazy.
const Timer = ({ seconds }) => {
const [timeLeft, setTimeLeft] = useState('');
const now = Date.now();
const then = now + seconds * 1000;
const countDown = setInterval(() => {
const secondsLeft = Math.round((then - Date.now()) / 1000);
if(secondsLeft <= 0) {
clearInterval(countDown);
console.log('done!');
return;
}
displayTimeLeft(secondsLeft);
}, 1000);
const displayTimeLeft = seconds => {
let minutesLeft = Math.floor(seconds/60) ;
let secondsLeft = seconds % 60;
minutesLeft = minutesLeft.toString().length === 1 ? "0" + minutesLeft : minutesLeft;
secondsLeft = secondsLeft.toString().length === 1 ? "0" + secondsLeft : secondsLeft;
return `${minutesLeft}:${secondsLeft}`;
}
useEffect(() => {
setInterval(() => {
setTimeLeft(displayTimeLeft(seconds));
}, 1000);
}, [seconds])
return (
<div><h1>{timeLeft}</h1></div>
)
}
export default Timer;```
Solution 1:[1]
const Timer = ({ seconds }) => {
// initialize timeLeft with the seconds prop
const [timeLeft, setTimeLeft] = useState(seconds);
useEffect(() => {
// exit early when we reach 0
if (!timeLeft) return;
// save intervalId to clear the interval when the
// component re-renders
const intervalId = setInterval(() => {
setTimeLeft(timeLeft - 1);
}, 1000);
// clear interval on re-render to avoid memory leaks
return () => clearInterval(intervalId);
// add timeLeft as a dependency to re-rerun the effect
// when we update it
}, [timeLeft]);
return (
<div>
<h1>{timeLeft}</h1>
</div>
);
};
Solution 2:[2]
You should use setInterval
. I just wanted to add a slight improvement over @Asaf solution. You do not have to reset the interval every time you change the value. It's gonna remove the interval and add a new one every time (Might as well use a setTimeout
in that case). So you can remove the dependencies of your useEffect
(i.e. []
):
function Countdown({ seconds }) {
const [timeLeft, setTimeLeft] = useState(seconds);
useEffect(() => {
const intervalId = setInterval(() => {
setTimeLeft((t) => t - 1);
}, 1000);
return () => clearInterval(intervalId);
}, []);
return <div>{timeLeft}s</div>;
}
Working example:
Note in the setter, we need to use this syntax (t) => t - 1
so that we get the latest value each time (see: https://reactjs.org/docs/hooks-reference.html#functional-updates).
Edit (22/10/2021)
If you want to use a setInterval
and stop the counter at 0, here is what you can do:
function Countdown({ seconds }) {
const [timeLeft, setTimeLeft] = useState(seconds);
const intervalRef = useRef(); // Add a ref to store the interval id
useEffect(() => {
intervalRef.current = setInterval(() => {
setTimeLeft((t) => t - 1);
}, 1000);
return () => clearInterval(intervalRef.current);
}, []);
// Add a listener to `timeLeft`
useEffect(() => {
if (timeLeft <= 0) {
clearInterval(intervalRef.current);
}
}, [timeLeft]);
return <div>{timeLeft}s</div>;
}
Solution 3:[3]
Here's another alternative with setTimeout
const useCountDown = (start) => {
const [counter, setCounter] = useState(start);
useEffect(() => {
if (counter === 0) {
return;
}
setTimeout(() => {
setCounter(counter - 1);
}, 1000);
}, [counter]);
return counter;
};
Example
Solution 4:[4]
Here's my version of a hook, with a "stop" countdown. Also, I added a "fps" (frames p/sec), to show the countdown with decimal places!
import { useEffect, useRef, useState } from 'react'
interface ITimer {
timer: number
startTimer: (time: number) => void
stopTimer: () => void
}
interface IProps {
start?: number
fps?: number
}
const useCountDown = ({ start, fps }: IProps): ITimer => {
const [timer, setTimer] = useState(start || 0)
const intervalRef = useRef<NodeJS.Timer>()
const stopTimer = () => {
if (intervalRef.current) clearInterval(intervalRef.current)
}
const startTimer = (time: number) => {
setTimer(time)
}
useEffect(() => {
if (timer <= 0) return stopTimer()
intervalRef.current = setInterval(() => {
setTimer((t) => t - 1 / (fps || 1))
}, 1000 / (fps || 1))
return () => {
if (intervalRef.current) clearInterval(intervalRef.current)
}
}, [timer])
return { timer, startTimer, stopTimer }
}
export default useCountDown
Sources
This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.
Source: Stack Overflow
Solution | Source |
---|---|
Solution 1 | Asaf Aviv |
Solution 2 | |
Solution 3 | Jose |
Solution 4 | Bruno Lobo |