Chrono

Chrono is a minimal library to simplify working with dates in Javascript. It has built-in locale and timezone support.

Concepts

• Installation
• Documentation
• DateTime
• Interval
• Time

Installation

yarn install @bedrockio/chrono

Documentation

https://bedrockio.github.io/chrono/

DateTime

The DateTime object maintains basic parity with the built-in Date object, however is immutable and has a number of additional methods:

import { DateTime } from '@bedrockio/chrono';

const now = new DateTime();

// Unlike JS dates, the "set" methods return
// a new instance and do not mutate the date.
const january = now.setMonth(0);

Timezones and locales can be set on each instance or globally:

// Sets the timezone for this DateTime
const dt = new DateTime({
  timeZone: 'America/New_York',
  locale: 'en-US',
});

DateTime.setTimeZone('America/New_York');
DateTime.setLocale('en-US');

Date Formatting

For common formats there are convenience methods. For full control, the format method accepts a locale options object or a token string.

Convenience Methods

const dt = new DateTime('2020-01-01T14:00:00.000Z', {
  timeZone: 'America/New_York',
});

dt.toLong();   // "January 1, 2020 at 9:00am"
dt.toMedium(); // "Jan 1, 2020, 9:00am"
dt.toShort();  // "1/1/2020, 9:00am"

dt.toDateLong();   // "January 1, 2020"
dt.toDateMedium(); // "Jan 1, 2020"
dt.toDateShort();  // "1/1/2020"

dt.toTimeLong();   // "9:00:00am"
dt.toTimeMedium(); // "9:00am"
dt.toTimeShort();  // "9am"

dt.toLongWithZone();       // "January 1, 2020 at 9:00am GMT-5"
dt.toLongWithZone('long'); // "January 1, 2020 at 9:00am Eastern Standard Time"
dt.toTimeWithZone();       // "9:00am GMT-5"

Locale Formatting

Passing an object to format uses Intl.DateTimeFormat to produce a human-readable string in a specific locale. The locale used in order will be:

• Passed in the options to format
• The internal locale of the DateTime
• The globally set locale
• The system locale

const dt = new DateTime('2020-01-01T14:00:00.000Z', {
  timeZone: 'America/New_York',
});

dt.format({
  year: 'numeric',
  month: 'long',
  day: 'numeric',
});
// "January 1, 2020"

Token Formatting

Passing a string will format the date using tokens and ignoring locales.

const dt = new DateTime('2020-01-01T14:00:00.000Z', {
  timeZone: 'America/New_York',
});

dt.format('h:mm a');   // "9:00 am"
dt.format('M/d/yyyy'); // "1/1/2020"

Supported tokens are:

Token	Description
yy	two-digit year
yyyy	four to six digit year
M	unpadded month
MM	padded month
d	unpadded day of the month
dd	padded day of the month
h	unpadded hour in 12-hour time
hh	padded hour in 12-hour time
H	unpadded hour in 24-hour time
HH	padded hour in 24-hour time
m	unpadded minute
mm	padded minute
s	unpadded second
ss	padded second
a	lowercase meridiem (am/pm)
A	uppercase meridiem (AM/PM)
Z	narrow timezone offset (-5)
ZZ	short timezone offset (-0500)
ZZZ	long timezone offset (-05:00)
ZZZZ	short timezone name (EST)
ZZZZZ	long timezone name (Eastern Standard Time)

Native Date Compatibility

DateTime provides passthroughs to the standard Date methods (toUTCString, toLocaleString, toJSON, etc.) so that it can stand in for a Date in code that calls them. Each delegates directly to the underlying Date and produces exactly what the spec defines.

The one exception is toString, which deliberately diverges from the native form to produce a more readable result for implicit stringification (template literals, logs, errors). Use dt.date.toString() if you need the literal native format.

Interval

The Interval object represents an interval of time:

import { DateTime, Interval } from '@bedrockio/chrono';

const lastYear = new DateTime().rewind(1, 'year');
const nextYear = new DateTime().advance(1, 'year');

const interval = new Interval(lastYear, nextYear);

// The number of days in this interval.
const days = interval.days();

Time

The Time object represents a generic time of day, with no associated date or timezone. It is useful for representing times in the abstract — for scheduling, display, or comparison — without binding to a specific calendar moment.

import { Time } from '@bedrockio/chrono';

const noon = new Time(12, 0);
const meeting = new Time('9:30am');
const duration = new Time(35100000); // 9:45:00.000

// Like DateTime, Time is immutable.
const later = meeting.advance(15, 'minutes'); // "9:45am"

Hours greater than 24 are allowed and preserved (not normalized), which lets a Time represent times that spill past midnight — useful for broadcast schedules or late-night programming:

new Time('25:30').toISOString(); // "25:30:00.000"