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Learn JS #19

June 14 • 5:09 pm

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JavaScript Date Formats

JavaScript Date Input

There are generally 3 types of JavaScript date input formats:

Type Example
ISO Date “2015-03-25” (The International Standard)
Short Date “03/25/2015”
Long Date “Mar 25 2015” or “25 Mar 2015”

The ISO format follows a strict standard in JavaScript.

The other formats are not so well defined and might be browser specific.

JavaScript Date Output

Independent of input format, JavaScript will (by default) output dates in full text string format:

Tue Jun 14 2022 14:51:25 GMT+0300 (Eastern European Summer Time)

JavaScript ISO Dates

ISO 8601 is the international standard for the representation of dates and times.

The ISO 8601 syntax (YYYY-MM-DD) is also the preferred JavaScript date format:

Example (Complete date)

const d = new Date("2015-03-25");

The computed date will be relative to your time zone.
Depending on your time zone, the result above will vary between March 24 and March 25.

ISO Dates (Year and Month)

ISO dates can be written without specifying the day (YYYY-MM):

Example

const d = new Date("2015-03");

Time zones will vary the result above between February 28 and March 01.

ISO Dates (Only Year)

ISO dates can be written without month and day (YYYY):

Example

const d = new Date("2015");

Time zones will vary the result above between December 31 2014 and January 01 2015.

ISO Dates (Date-Time)

ISO dates can be written with added hours, minutes, and seconds (YYYY-MM-DDTHH:MM:SSZ):

Example

const d = new Date("2015-03-25T12:00:00Z");

Date and time is separated with a capital T.

UTC time is defined with a capital letter Z.

If you want to modify the time relative to UTC, remove the Z and add +HH:MM or -HH:MM instead:

Example

const d = new Date("2015-03-25T12:00:00-06:30");

UTC (Universal Time Coordinated) is the same as GMT (Greenwich Mean Time).

Omitting T or Z in a date-time string can give different results in different browsers.

Time Zones

When setting a date, without specifying the time zone, JavaScript will use the browser’s time zone.

When getting a date, without specifying the time zone, the result is converted to the browser’s time zone.

In other words: If a date/time is created in GMT (Greenwich Mean Time), the date/time will be converted to CDT (Central US Daylight Time) if a user browses from central US.

JavaScript Short Dates.

Short dates are written with an “MM/DD/YYYY” syntax like this:

Example

const d = new Date("03/25/2015");

WARNINGS !

In some browsers, months or days with no leading zeroes may produce an error:

const d = new Date("2015-3-25");

The behavior of “YYYY/MM/DD” is undefined.
Some browsers will try to guess the format. Some will return NaN.

const d = new Date("2015/03/25");

The behavior of  “DD-MM-YYYY” is also undefined.
Some browsers will try to guess the format. Some will return NaN.

const d = new Date("25-03-2015");

JavaScript Long Dates.

Long dates are most often written with a “MMM DD YYYY” syntax like this:

Example

const d = new Date("Mar 25 2015");

Month and day can be in any order:

Example

const d = new Date("25 Mar 2015");

And, month can be written in full (January), or abbreviated (Jan):

Example

const d = new Date("January 25 2015");

Example

const d = new Date("Jan 25 2015");

Commas are ignored. Names are case insensitive:

Example

const d = new Date("JANUARY, 25, 2015");

Date Input – Parsing Dates

If you have a valid date string, you can use the Date.parse() method to convert it to milliseconds.

Date.parse() returns the number of milliseconds between the date and January 1, 1970:

Example

let msec = Date.parse("March 21, 2012");

You can then use the number of milliseconds to convert it to a date object:

Example

let msec = Date.parse("March 21, 2012");
const d = new Date(msec);

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