JavaScript

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Description

JavaScript often abbreviated JS, is a programming language that is one of the core technologies of the World Wide Web, alongside HTML and CSS. Over 97% of websites use JavaScript on the client side for web page behavior, often incorporating third-party libraries. All major web browsers have a dedicated JavaScript engine to execute the code on users' devices.

JavaScript is a high-level, often just-in-time compiled language that conforms to the ECMAScript standard. It has dynamic typing, prototype-based object-orientation, and first-class functions. It is multi-paradigm, supporting event-driven, functional, and imperative programming styles. It has application programming interfaces (APIs) for working with text, dates, regular expressions, standard data structures, and the Document Object Model (DOM).

The ECMAScript standard does not include any input/output (I/O), such as networking, storage, or graphics facilities. In practice, the web browser or other runtime system provides JavaScript APIs for I/O.

JavaScript engines were originally used only in web browsers, but are now core components of some servers and a variety of applications. The most popular runtime system for this usage is Node.js.

Although Java and JavaScript are similar in name, syntax, and respective standard libraries, the two languages are distinct and differ greatly in design.

Datatypes

Datetime

Formatting

MomentJS formatting

moment().format(); moment().format(String);

This is the most robust display option. It takes a string of tokens and replaces them with their corresponding values.

moment().format();                                // "2014-09-08T08:02:17-05:00" (ISO 8601, no fractional seconds)
moment().format("dddd, MMMM Do YYYY, h:mm:ss a"); // "Sunday, February 14th 2010, 3:25:50 pm"
moment().format("ddd, hA");                       // "Sun, 3PM"
moment().format("[Today is] dddd");               // "Today is Sunday"
moment('gibberish').format('YYYY MM DD');         // "Invalid date"

X was added in 2.0.0.

e E gg gggg GG GGGG were added in 2.1.0.

x was added in 2.8.4.

SSSS to SSSSSSSSS were added in 2.10.5. They display 3 significant digits and the rest is filled with zeros.

k and kk were added in 2.13.0.

Localized formats

Because preferred formatting differs based on locale, there are a few tokens that can be used to format a moment based on its locale.

There are upper and lower case variations on the same formats. The lowercase version is intended to be the shortened version of its uppercase counterpart.

l ll lll llll are available in 2.0.0.LTS was added in 2.8.4.

Escaping characters

To escape characters in format strings, you can wrap the characters in square brackets.

moment().format('[today] dddd'); // 'today Sunday'

Similarities and differences with LDML

Note: While these date formats are very similar to LDML date formats, there are a few minor differences regarding day of month, day of year, and day of week.

For a breakdown of a few different date formatting tokens across different locales, see this chart of date formatting tokens.

Formatting speed

To compare Moment.js formatting speed against other libraries, check out this comparison against other libraries.

Other tokens

If you are more comfortable working with strftime instead of LDML-like parsing tokens, you can use Ben Oakes' plugin. benjaminoakes/moment-strftime.

Default format

Calling moment#format without a format will default to moment.defaultFormat. Out of the box, moment.defaultFormat is the ISO8601 format YYYY-MM-DDTHH:mm:ssZ.

As of version 2.13.0, when in UTC mode, the default format is governed by moment.defaultFormatUtc which is in the format YYYY-MM-DDTHH:mm:ss[Z]. This returns Z as the offset, instead of +00:00.

In certain instances, a local timezone (such as Atlantic/Reykjavik) may have a zero offset, and will be considered to be UTC. In such cases, it may be useful to set moment.defaultFormat and moment.defaultFormatUtc to use the same formatting.

Changing the value of moment.defaultFormat will only affect formatting, and will not affect parsing. for example:

moment.defaultFormat = "DD.MM.YYYY HH:mm";
// parse with .toDate()
moment('20.07.2018 09:19').toDate() // Invalid date
// format the date string with the new defaultFormat then parse
moment('20.07.2018 09:19', moment.defaultFormat).toDate() // Fri Jul 20 2018 09:19:00 GMT+0300