React <Countdown />

A customizable countdown component for React.

• Getting Started
• Motivation
• Examples
• Props
• API Reference
• Helpers
• FAQ
• Contributing
• License

Getting Started

You can install the module via npm or yarn:

1npm install react-countdown --save

1yarn add react-countdown

Motivation

As part of a small web app at first, the idea was to separate the countdown component from the main package to combine general aspects of the development with React, testing with Jest and more things that relate to publishing a new Open Source project.

Examples

Here are some examples which you can try directly online. You can also clone this repo and explore some more examples in there by running yarn start within the examples folder.

Basic Usage

A very simple and minimal example of how to set up a countdown that counts down from 10 seconds.

1import React from 'react';
2import ReactDOM from 'react-dom';
3import Countdown from 'react-countdown';
4
5ReactDOM.render(
6  <Countdown date={Date.now() + 10000} />,
7  document.getElementById('root')
8);

Live Demo

Custom & Conditional Rendering

In case you want to change the output of the component or want to signal that the countdown's work is done, you can do this by either using the onComplete callback, a custom renderer, or by specifying a React child within <Countdown></Countdown>, which will only be shown once the countdown is complete.

Using a React Child for the Completed State

1import React from 'react';
2import ReactDOM from 'react-dom';
3import Countdown from 'react-countdown';
4
5// Random component
6const Completionist = () => <span>You are good to go!</span>;
7
8ReactDOM.render(
9  (
10    <Countdown date={Date.now() + 5000}>
11      <Completionist />
12    </Countdown>
13  ),
14  document.getElementById('root')
15);

Live Demo

Custom Renderer with Completed Condition

1import React from 'react';
2import ReactDOM from 'react-dom';
3import Countdown from 'react-countdown';
4
5// Random component
6const Completionist = () => <span>You are good to go!</span>;
7
8// Renderer callback with condition
9const renderer = ({ hours, minutes, seconds, completed }) => {
10  if (completed) {
11    // Render a completed state
12    return <Completionist />;
13  } else {
14    // Render a countdown
15    return <span>{hours}:{minutes}:{seconds}</span>;
16  }
17};
18
19ReactDOM.render(
20  <Countdown
21    date={Date.now() + 5000}
22    renderer={renderer}
23  />,
24  document.getElementById('root')
25);

Live Demo

Countdown in Milliseconds

Here is an example with a countdown of 10 seconds that displays the total time difference in milliseconds. In order to display the milliseconds appropriately, the intervalDelay value needs to be lower than 1000ms and a precision of 1 to 3 should be used. Last but not least, a simple renderer callback needs to be set up.

1import React from 'react';
2import ReactDOM from 'react-dom';
3import Countdown from 'react-countdown';
4
5ReactDOM.render(
6  <Countdown
7    date={Date.now() + 10000}
8    intervalDelay={0}
9    precision={3}
10    renderer={props => <div>{props.total}</div>}
11  />,
12  document.getElementById('root')
13);

Live Demo

Props

Name	Type	Default	Description
date	Date|string|number	required	Date or timestamp in the future
key	string|number	undefined	React key; can be used to restart the countdown
daysInHours	boolean	false	Days are calculated as hours
zeroPadTime	number	2	Length of zero-padded output, e.g.: 00:01:02
zeroPadDays	number	zeroPadTime	Length of zero-padded days output, e.g.: 01
controlled	boolean	false	Hands over the control to its parent(s)
intervalDelay	number	1000	Interval delay in milliseconds
precision	number	0	The precision on a millisecond basis
autoStart	boolean	true	Countdown auto-start option
overtime	boolean	false	Counts down to infinity
children	any	null	A React child for the countdown's completed state
renderer	function	undefined	Custom renderer callback
now	function	Date.now	Alternative handler for the current date
onMount	function	undefined	Callback when component mounts
onStart	function	undefined	Callback when countdown starts
onPause	function	undefined	Callback when countdown pauses
onStop	function	undefined	Callback when countdown stops
onTick	function	undefined	Callback on every interval tick (controlled = false)
onComplete	function	undefined	Callback when countdown ends

date

The date prop is the only required one and can be a Date object, string, or timestamp in the future. By default, this date is compared with the current date, or a custom handler defined via now.

Valid values can be (and more):

• '2020-02-01T01:02:03' // Date time string format
• 1580518923000 // Timestamp in milliseconds
• new Date(1580518923000) // Date object

key

This is one of React's internal component props to help identify elements throughout the reconciliation process. It can be used to restart the countdown by passing in a new string or number value.

Please see official React docs for more information about keys.

daysInHours

Defines whether the time of day should be calculated as hours rather than separated days.

controlled

Can be useful if the countdown's interval and/or date control should be handed over to the parent. In case controlled is true, the provided date will be treated as the countdown's actual time difference and not be compared to now anymore.

zeroPadTime

This option defaults to 2 in order to display the common format 00:00:00 instead of 0:0:0. If the value is higher than 2, only the hours part (see zeroPadDays for days) will be zero-padded while it stays at 2 for minutes as well as seconds. If the value is lower, the output won't be zero-padded like the example before is showing.

zeroPadDays

Defaults to zeroPadTime. It works the same way as zeroPadTime does, just for days.

intervalDelay

Since this countdown is based on date comparisons, the default value of 1000 milliseconds is probably enough for most scenarios and doesn't need to be changed.

However, if it needs to be more precise, the intervalDelay can be set to something lower - down to 0, which would, for example, allow showing the milliseconds in a more fancy way (currently only possible through a custom renderer).

precision

In certain cases, you might want to base off the calculations on a millisecond basis. The precision prop, which defaults to 0, can be used to refine this calculation. While the default value simply strips the milliseconds part (e.g., 10123ms => 10000ms), a precision of 3 leads to 10123ms.

autoStart

Defines whether the countdown should start automatically or not. Defaults to true.

overtime

Defines whether the countdown can go into overtime by extending its lifetime past the targeted endpoint. Defaults to false.

When set to true, the countdown timer won't stop when hitting 0, but instead becomes negative and continues to run unless paused/stopped. The onComplete callback would still get triggered when the initial countdown phase completes.

Please note that the children prop will be ignored if overtime is true. Also, when using a custom renderer, you'll have to check one of the render props, e.g., total, or completed, to render the overtime output.

children

This component also considers the child that may live within the <Countdown></Countdown> element, which, in case it's available, replaces the countdown's component state once it's complete. Moreover, an additional prop called countdown is set and contains data similar to what the renderer callback would receive. Here's an example that showcases its usage.

Please note that the children prop will be ignored if a custom renderer is defined.

renderer

The component's raw render output is kept very simple.

For more advanced countdown displays, a custom renderer callback can be defined to return a new React element. It receives the following render props as the first argument.

Render Props

The render props object consists of the current time delta object, the countdown's api, the component props, and last but not least, a formatted object.

1{
2  total: 0,
3  days: 0,
4  hours: 0,
5  minutes: 0,
6  seconds: 0,
7  milliseconds: 0,
8  completed: true,
9  api: { ... },
10  props: { ... },
11  formatted: { ... }
12}

Please note that a defined custom renderer will ignore the children prop.

now

If the current date and time (determined via a reference to Date.now) is not the right thing to compare with for you, a reference to a custom function that returns a similar dynamic value could be provided as an alternative.

onMount

onMount is a callback and triggered when the countdown mounts. It receives a time delta object as the first argument.

onStart

onStart is a callback and triggered whenever the countdown is started (including first-run). It receives a time delta object as the first argument.

onPause

onPause is a callback and triggered every time the countdown is paused. It receives a time delta object as the first argument.

onStop

onStop is a callback and triggered every time the countdown is stopped. It receives a time delta object as the first argument.

onTick

onTick is a callback and triggered every time a new period is started, based on what the intervalDelay's value is. It only gets triggered when the countdown's controlled prop is set to false, meaning that the countdown has full control over its interval. It receives a time delta object as the first argument.

onComplete

onComplete is a callback and triggered whenever the countdown ends. In contrast to onTick, the onComplete callback also gets triggered in case controlled is set to true. It receives a time delta object as the first argument and a boolean as a second argument, indicating whether the countdown transitioned into the completed state (false) or completed on start (true).

API Reference

The countdown component exposes a simple API through the getApi() function that can be accessed via component ref. It is also part (api) of the render props passed into renderer if needed. Here's an example of how to use it.

start()

Starts the countdown in case it is paused/stopped or needed when autoStart is set to false.

pause()

Pauses the running countdown. This only works as expected if the controlled prop is set to false because calcTimeDelta calculates an offset time internally.

stop()

Stops the countdown. This only works as expected if the controlled prop is set to false because calcTimeDelta calculates an offset time internally.

isPaused()

Returns a boolean for whether the countdown has been paused or not.

isStopped()

Returns a boolean for whether the countdown has been stopped or not.

isCompleted()

Returns a boolean for whether the countdown has been completed or not.

Please note that this will always return false if overtime is true. Nevertheless, an into overtime running countdown's completed state can still be looking at the time delta object's completed value.

Helpers

This module also exports three simple helper functions, which can be utilized to build your own countdown custom renderer.

1import Countdown, { zeroPad, calcTimeDelta, formatTimeDelta } from 'react-countdown';

zeroPad(value, [length = 2])

The zeroPad function transforms and returns a given value with padded zeros depending on the length. The value can be a string or number, while the length parameter can be a number, defaulting to 2. Returns the zero-padded string, e.g., zeroPad(5) => 05.

1const renderer = ({ hours, minutes, seconds }) => (
2  <span>
3    {zeroPad(hours)}:{zeroPad(minutes)}:{zeroPad(seconds)}
4  </span>
5);

calcTimeDelta(date, [options])

calcTimeDelta calculates the time difference between a given end date and the current date (now). It returns, similar to the renderer callback, a custom object (also referred to as countdown time delta object) with the following time-related data:

1{ total, days, hours, minutes, seconds, milliseconds, completed }

The total value is the absolute time difference in milliseconds, whereas the other time-related values contain their relative portion of the current time difference. The completed value signalizes whether the countdown reached its initial end or not.

The calcTimeDelta function accepts two arguments in total; only the first one is required.

date Date or timestamp representation of the end date. See date prop for more details.

options The second argument consists of the following optional keys.

• now = Date.now Alternative function for returning the current date, also see now.

• precision = 0 The precision on a millisecond basis.

• controlled = false Defines whether the calculated value is provided in a controlled environment as the time difference or not.

• offsetTime = 0 Defines the offset time that gets added to the start time; only considered if controlled is false.

• overtime = false Defines whether the time delta can go into overtime and become negative or not. When set to true, the total could become negative, at which point completed will still be set to true.

formatTimeDelta(timeDelta, [options])

formatTimeDelta formats a given countdown time delta object. It returns the formatted portion of it, equivalent to:

1{
2  days: '00',
3  hours: '00',
4  minutes: '00',
5  seconds: '00',
6}

This function accepts two arguments in total; only the first one is required.

timeDelta Time delta object, e.g., returned by calcTimeDelta.

options The options object consists of the following three component props and is used to customize the time delta object's formatting:

• daysInHours
• zeroPadTime
• zeroPadDays

FAQ

Why does my countdown reset on every re-render?

A common reason for this is that the date prop gets passed directly into the component without persisting it in any way.

In order to avoid this from happening, it should be stored in a place that persists throughout lifecycle changes, for example, in the component's local state.

Why aren't my values formatted when using the custom renderer?

The renderer callback gets called with a time delta object that also consists of a formatted object which holds these formatted values.

Why do I get this error "Warning: Text content did not match..."?

This could have something to do with server-side rendering and that the countdown already runs on the server-side, resulting in a timestamp discrepancy between the client and the server. In this case, it might be worth checking https://reactjs.org/docs/dom-elements.html#suppresshydrationwarning.

Alternatively, you could try to set autoStart to false and start the countdown through the API once it's available on the client. Here are some related issues that might help in fixing this problem.

Contributing

Contributions of any kind are very welcome. Read more in our contributing guide about how to report bugs, create pull requests, and other development-related topics.

License

MIT