content/snippets/react/s/count-down.md
---
title: Countdown timer
type: snippet
language: react
tags: [components,state]
cover: sea-view-2
dateModified: 2021-10-13
---
Renders a countdown timer that prints a message when it reaches zero.
- Use the `useState()` hook to create a state variable to hold the time value. Initialize it from the props and destructure it into its components.
- Use the `useState()` hook to create the `paused` and `over` state variables, used to prevent the timer from ticking if it's paused or the time has run out.
- Create a method `tick`, that updates the time values based on the current value (i.e. decreasing the time by one second).
- Create a method `reset`, that resets all state variables to their initial states.
- Use the the `useEffect()` hook to call the `tick` method every second via the use of `setInterval()` and use `clearInterval()` to clean up when the component is unmounted.
- Use `String.prototype.padStart()` to pad each part of the time array to two characters to create the visual representation of the timer.
```jsx
const CountDown = ({ hours = 0, minutes = 0, seconds = 0 }) => {
const [paused, setPaused] = React.useState(false);
const [over, setOver] = React.useState(false);
const [[h, m, s], setTime] = React.useState([hours, minutes, seconds]);
const tick = () => {
if (paused || over) return;
if (h === 0 && m === 0 && s === 0) setOver(true);
else if (m === 0 && s === 0) {
setTime([h - 1, 59, 59]);
} else if (s == 0) {
setTime([h, m - 1, 59]);
} else {
setTime([h, m, s - 1]);
}
};
const reset = () => {
setTime([parseInt(hours), parseInt(minutes), parseInt(seconds)]);
setPaused(false);
setOver(false);
};
React.useEffect(() => {
const timerID = setInterval(() => tick(), 1000);
return () => clearInterval(timerID);
});
return (
<div>
<p>{`${h.toString().padStart(2, '0')}:${m
.toString()
.padStart(2, '0')}:${s.toString().padStart(2, '0')}`}</p>
<div>{over ? "Time's up!" : ''}</div>
<button onClick={() => setPaused(!paused)}>
{paused ? 'Resume' : 'Pause'}
</button>
<button onClick={() => reset()}>Restart</button>
</div>
);
};
ReactDOM.createRoot(document.getElementById('root')).render(
<CountDown hours={1} minutes={45} />
);
```