Awesome

dateformat

A node.js package for Steven Levithan's excellent dateFormat() function.

Modifications

Removed the Date.prototype.format method. Sorry folks, but extending native prototypes is for suckers.
Added a module.exports = dateFormat; statement at the bottom
Added the placeholder N to get the ISO 8601 numeric representation of the day of the week

Installation

$ npm install dateformat
$ dateformat --help

Usage

As taken from Steven's post, modified to match the Modifications listed above:

import dateFormat, { masks } from "dateformat";
const now = new Date();

// Basic usage
dateFormat(now, "dddd, mmmm dS, yyyy, h:MM:ss TT");
// Saturday, June 9th, 2007, 5:46:21 PM

// You can use one of several named masks
dateFormat(now, "isoDateTime");
// 2007-06-09T17:46:21

// ...Or add your own
masks.hammerTime = 'HH:MM! "Can\'t touch this!"';
dateFormat(now, "hammerTime");
// 17:46! Can't touch this!

// You can also provide the date as a string
dateFormat("Jun 9 2007", "fullDate");
// Saturday, June 9, 2007

// Note that if you don't include the mask argument,
// dateFormat.masks.default is used
dateFormat(now);
// Sat Jun 09 2007 17:46:21

// And if you don't include the date argument,
// the current date and time is used
dateFormat();
// Sat Jun 09 2007 17:46:22

// You can also skip the date argument (as long as your mask doesn't
// contain any numbers), in which case the current date/time is used
dateFormat("longTime");
// 5:46:22 PM EST

// And finally, you can convert local time to UTC time. Simply pass in
// true as an additional argument (no argument skipping allowed in this case):
dateFormat(now, "longTime", true);
// 10:46:21 PM UTC

// ...Or add the prefix "UTC:" or "GMT:" to your mask.
dateFormat(now, "UTC:h:MM:ss TT Z");
// 10:46:21 PM UTC

// You can also get the ISO 8601 week of the year:
dateFormat(now, "W");
// 42

// and also get the ISO 8601 numeric representation of the day of the week:
dateFormat(now, "N");
// 6

Mask options

Mask	Description
`d`	Day of the month as digits; no leading zero for single-digit days.
`dd`	Day of the month as digits; leading zero for single-digit days.
`ddd`	Day of the week as a three-letter abbreviation.
`DDD`	"Ysd", "Tdy" or "Tmw" if date lies within these three days. Else fall back to ddd.
`dddd`	Day of the week as its full name.
`DDDD`	"Yesterday", "Today" or "Tomorrow" if date lies within these three days. Else fall back to dddd.
`m`	Month as digits; no leading zero for single-digit months.
`mm`	Month as digits; leading zero for single-digit months.
`mmm`	Month as a three-letter abbreviation.
`mmmm`	Month as its full name.
`yy`	Year as last two digits; leading zero for years less than 10.
`yyyy`	Year represented by four digits.
`h`	Hours; no leading zero for single-digit hours (12-hour clock).
`hh`	Hours; leading zero for single-digit hours (12-hour clock).
`H`	Hours; no leading zero for single-digit hours (24-hour clock).
`HH`	Hours; leading zero for single-digit hours (24-hour clock).
`M`	Minutes; no leading zero for single-digit minutes.
`MM`	Minutes; leading zero for single-digit minutes.
`N`	ISO 8601 numeric representation of the day of the week.
`o`	GMT/UTC timezone offset, e.g. -0500 or +0230.
`p`	GMT/UTC timezone offset, e.g. -05:00 or +02:30.
`s`	Seconds; no leading zero for single-digit seconds.
`ss`	Seconds; leading zero for single-digit seconds.
`S`	The date's ordinal suffix (st, nd, rd, or th). Works well with `d`.
`l`	Milliseconds; gives 3 digits.
`L`	Milliseconds; gives 2 digits.
`t`	Lowercase, single-character time marker string: a or p.
`tt`	Lowercase, two-character time marker string: am or pm.
`T`	Uppercase, single-character time marker string: A or P.
`TT`	Uppercase, two-character time marker string: AM or PM.
`W`	ISO 8601 week number of the year, e.g. 4, 42
`WW`	ISO 8601 week number of the year, leading zero for single-digit, e.g. 04, 42
`Z`	US timezone abbreviation, e.g. EST or MDT. For non-US timezones, the GMT/UTC offset is returned, e.g. GMT-0500
`'...'`, `"..."`	Literal character sequence. Surrounding quotes are removed.
`UTC:`	Must be the first four characters of the mask. Converts the date from local time to UTC/GMT/Zulu time before applying the mask. The "UTC:" prefix is removed.

Named Formats

Name	Mask	Example
`default`	`ddd mmm dd yyyy HH:MM:ss`	Sat Jun 09 2007 17:46:21
`shortDate`	`m/d/yy`	6/9/07
`paddedShortDate`	`mm/dd/yyyy`	06/09/2007
`mediumDate`	`mmm d, yyyy`	Jun 9, 2007
`longDate`	`mmmm d, yyyy`	June 9, 2007
`fullDate`	`dddd, mmmm d, yyyy`	Saturday, June 9, 2007
`shortTime`	`h:MM TT`	5:46 PM
`mediumTime`	`h:MM:ss TT`	5:46:21 PM
`longTime`	`h:MM:ss TT Z`	5:46:21 PM EST
`isoDate`	`yyyy-mm-dd`	2007-06-09
`isoTime`	`HH:MM:ss`	17:46:21
`isoDateTime`	`yyyy-mm-dd'T'HH:MM:sso`	2007-06-09T17:46:21+0700
`isoUtcDateTime`	`UTC:yyyy-mm-dd'T'HH:MM:ss'Z'`	2007-06-09T22:46:21Z

Localization

Day names, month names and the AM/PM indicators can be localized by passing an object with the necessary strings. For example:

import { i18n } from "dateformat";

i18n.dayNames = [
  "Sun",
  "Mon",
  "Tue",
  "Wed",
  "Thu",
  "Fri",
  "Sat",
  "Sunday",
  "Monday",
  "Tuesday",
  "Wednesday",
  "Thursday",
  "Friday",
  "Saturday",
];

i18n.monthNames = [
  "Jan",
  "Feb",
  "Mar",
  "Apr",
  "May",
  "Jun",
  "Jul",
  "Aug",
  "Sep",
  "Oct",
  "Nov",
  "Dec",
  "January",
  "February",
  "March",
  "April",
  "May",
  "June",
  "July",
  "August",
  "September",
  "October",
  "November",
  "December",
];

i18n.timeNames = ["a", "p", "am", "pm", "A", "P", "AM", "PM"];

Notice that only one language is supported at a time and all strings must be present in the new value.

Breaking change in 2.1.0

2.1.0 was published with a breaking change, for those using localized strings.
2.2.0 has been published without the change, to keep packages refering to ^2.0.0 to continue working. This is now branch v2_2.
3.0.* contains the localized AM/PM change.