A countdown timer and stopwatch hook for React
npm install react-timer-and-stopwatchsh
npm install react-timer-and-stopwatch
`
Setup
There are three ways to set up the timer hook: countdown with a duration of time, countdown with a Unix timestamp in milliseconds, or as a stopwatch.
$3
To set up a timer with a duration, use the timerWithDuration object property on useTimer's options.create object parameter. Inside of timerWithDuration are two properties, time (required) and the optional directionOfTimeForward bool property. The time property takes either a number of milliseconds or alternatively a time object. The optional directionOfTimeForward bool property controls whether the direction of the timer will flow forward (start at 00:00:00) or backward (start at end, finish at 00:00:00). Time flows backward by default on Duration timers.
#### Example
`jsx
import { useTimer } from "react-timer-and-stopwatch";
const SomeReactComponent = () => {
const timer = useTimer({
create: {
timerWithDuration: {
time: { // Set a duration of 1 minute and 30 seconds
minutes: 1,
seconds: 30
}
}
}
});
return (
Time Left: {timer.timerText}
);
}
`
This span element will show the following each tick:
`
Time Left: 00:01:30
Time Left: 00:01:29
Time Left: 00:01:28
etc.
`
*
$3
To set up a timer with a Unix timestamp, use the timerWithUnixTimestamp object property on useTimer's options.create object parameter.
#### Example
`jsx
import { useTimer } from "react-timer-and-stopwatch";
const SomeReactComponent = () => {
const unixTimestamp = Date.now() + 10000; // 10 seconds in the future
const timer = useTimer({
create: {
timerWithUnixTimestamp: {
unixTimestampMilliseconds: unixTimestamp
}
}
});
return (
Time Left: {timer.timerText}
);
}
`
This span element will show the following each tick:
`
Time Left: 00:00:10
Time Left: 00:00:09
Time Left: 00:00:08
etc.
`
If you'd like the Unix timer to go past its finish and show the time elapsed since its finish in negative numbers, you can set the optional property continueAfterFinish to true on options.create.timerWithUnixTimestamp. By default it's set to false.
It's also easy to integrate a Unix timer with popular JavaScript time libraries such as Moment.js and Luxon because in the end all you need is the Unix time in milliseconds.
#### Moment.js example
`jsx
import { useTimer } from "react-timer-and-stopwatch";
import moment from 'moment';
const SomeReactComponent = () => {
const unixTimestamp = moment('2025-08-14T11:04:10.570Z').valueOf(); // Using an ISO 8601 timestamp
const timer = useTimer({
create: {
timerWithUnixTimestamp: {
unixTimestampMilliseconds: unixTimestamp
}
}
});
return (
Time Left: {timer.timerText}
);
}
`
*
$3
To set up a stopwatch, set the property stopwatch to an object on useTimer's options.create object parameter. There are two properties on the options object, intervalRate and includeMilliseconds, which can be useful here. If you'd like your stopwatch to count by milliseconds and show milliseconds in the output, change the optional properties intervalRate to something smaller than 1000 and includeMilliseconds to true in options. If not included, by default the stopwatch will count by seconds and not show milliseconds in timerText. It will also autostart by default, which can be disabled by setting the optional options property autostart to false.
#### Example
`jsx
import { useTimer } from "react-timer-and-stopwatch";
const SomeReactComponent = () => {
const timer = useTimer({
create: {
stopwatch: {}
},
includeMilliseconds: true,
intervalRate: 47
});
return (
Time Left: {timer.timerText}
);
}
`
If you'd like to start the stopwatch past 0, you can set the optional startAtMilliseconds property on create.stopwatch to the number of milliseconds you wish.
*
Timer Status Booleans
There are three booleans on the the timer object returned by useTimer which reflect whether the timer is finished (timerIsFinished), paused (timerIsPaused), or past its finish (pastFinish). The only time pastFinish can be true is with a Unix timer.
*
Control Functions
There are functions returned by useTimer which can pause, resume, and reset the timer/stopwatch. These are togglePause, pauseTimer, resumeTimer, and resetTimer.
#### Example
`jsx
const SomeReactComponent = () => {
const timer = useTimer({
create: {
timerWithDuration: {
time: { // Set to a duration of 30 seconds
seconds: 30
}
}
}
});
const {togglePause, pauseTimer, resumeTimer, resetTimer, timerIsPaused, timerText} = timer;
return (
<>
Time Left: {timerText}
);
}
`
resetTimer can reset the timer/stopwatch with the original options if no parameter is included, or you can include an options object in the first optional parameter (adjustedOptions) to either adjust the old options or replace the old options entirely. If you want to replace them, set the second optional parameter (replaceOptions) to true and be sure to include a new create object on your new options object.
#### Example
`jsx
const SomeReactComponent = () => {
const timer = useTimer({
create: {
timerWithDuration: {
time: { // Set to a duration of 30 seconds
seconds: 30
}
}
}
});
const {resetTimer timerText} = timer;
const resetAndAdjustOptions = () => { // These new options will essentially be patched onto the old options
resetTimer({
autoplay: false,
includeMilliseconds: true,
intervalRate: 37
});
}
const resetAndReplaceOptions = () => { // This will replace the old options entirely, effectively creating a new timer/stopwatch on reset
resetTimer({
create: {
stopwatch: {} // The timer was a Duration countdown timer, but after reset it will be a Stopwatch
},
includeMilliseconds: true,
intervalRate: 37
},
true);
}
const resetTimerWithOldOptions = () => {
resetTimer();
}
return (
<>
Time Left: {timerText}
);
}
`
There are also functions to add and subtract time from the current timer/stopwatch. These are addTime and subtractTime. Both take either a number of milliseconds or alternatively a time object.
#### Example
`jsx
const SomeReactComponent = () => {
const timer = useTimer({
create: {
timerWithDuration: {
time: { // Set to a duration of 1 day
days: 1
}
}
}
});
return (
<>
Time Left: {timer.timerText}
);
}
`
Note: none of these control functions affect Unix timestamp timers.
*
Customization
$3
There are two optional properties on useTimer's options object that affect the timer/stopwatch's timerText string output.
| Property | Type | Purpose | Default |
| ---- | ---- | ---- | ---- |
| textOutputWithWords | boolean | Whether the timerText string is only numbers, e.g. "00:01:45", or numbers with words, e.g. "1 minute, 45 seconds" | false, only numbers |
| includeMilliseconds | boolean | Whether milliseconds are included on the timerText string | false |
$3
There are several optional callbacks you can provide to the timer to fire at various points in time: an onTick callback that fires every interval, an onFinish callback that fires when the timer completes, and there are also arrays of callbacks you can provide for onProgress callbacks that fire at provided times into a timer and onTimeLeft callbacks that fire when there's a provided time left on the timer. onTimeLeft and onFinish callbacks will never fire on Stopwatches.
#### Example
`jsx
const SomeReactComponent = () => {
const timer = useTimer({
create: {
timerWithDuration: {
time: { // Set a duration of 1 minute and 30 seconds
minutes: 1,
seconds: 30
}
}
},
callbacks: {
onTick: () => console.log('This runs every interval.'),
onFinish: () => alert('The timer is done.'),
onProgress: [
{
time: { seconds: 10 },
callback: () => console.log('This is firing 10 seconds into the timer.')
},
{
time: { seconds: 20 },
callback: () => console.log('This is firing 20 seconds into the timer.')
}
],
onTimeLeft: [
{
time: { seconds: 5 },
callback: () => console.log('This is firing when there is 5 seconds left on the timer.')
},
{
time: { seconds: 3 },
callback: () => console.log('This is firing when there is 3 seconds left on the timer.')
},
]
}
});
return (
Time Left: {timer.timerText}
);
}
`
*
Misc Options
The rest of the optional customization properties you can include with the useTimer options object parameter:
| Property | Type | Purpose | Default |
| ------- | ------- | ------- | ------- |
| autoplay | boolean | Whether the timer starts right away. Has no effect on UnixTimestamps, which is always true. | true |
| includeMilliseconds | boolean | Includes milliseconds in timerText string | false |
| intervalRate | number | How many milliseconds between each interval tick. | 1000 |
| textOutputWithWords | boolean | If false timerText output is only numbers "01:20:10", or if true it includes words "1 hour, 20 minutes, 10 seconds" | false |
*
Timer Properties
Everything on the timer object returned from useTimer
| Property | Type | Purpose |
| ------- | ------- | ------- |
| timerText | string | The string representation of the timer/stopwatch, i.e., "00:01:30" or "1 minute, 30 seconds" depending on your settings |
| timerDisplayStrings | object | An object version of timerText, i.e., { days: "00", hours: "00", minutes: "01", seconds: "30", milliseconds: "000" }. If you need the number values of these for any reason, it's easy to convert by going Number(timerDisplayStrings.minutes) |
| timeElapsed | number | Elapsed time in milliseconds. Important: this number is updated every interval, not necessarily updated every millisecond (unless your intervalRate is set to 1) |
| timerIsPaused | boolean | Indicates whether the timer/stopwatch is currently paused |
| timerIsFinished | boolean | Indicates whether the timer has reached its end |
| pastFinish | boolean | Only relevant to Unix timers: indicates whether the timer has gone past its end |
| pauseTimer | function | Pauses timer/stopwatch when called |
| resumeTimer | function | Resumes timer/stopwatch when called |
| togglePause | function | When called it unpauses if timer/stopwatch is paused, pauses if timer/stopwatch is unpaused |
| resetTimer | function | Resets a timer/stopwatch to the beginning with originally supplied options, or with adjusted options, or with replaced options |
| addTime | function | Adds time to timer/stopwatch |
| subtractTime | function | Subtracts time from timer/stopwatch |
Common Parameters
| Property | Type | Purpose |
| ------- | ------- | ------- |
| time | number or time object | Any time you need to provide a representation of time in a time property in options, the property takes either a number of milliseconds or a time object, which is an object with keys of units of time (milliseconds, seconds, minutes, hours, and days) and values of numbers. |
*
Terminology
| Term | Definition |
| ---- | ---- |
| Time Object | An object that has keys of units of time (milliseconds, seconds, minutes, hours, and days`) and values of numbers. Example: { hours: 2, minutes: 20, seconds: 40 } |