Dates

Published Jul 30, 2021Updated Sep 5, 2023

In JavaScript, Date objects represent a single moment in time stored as a representation of the number of milliseconds since midnight on January 1st, 1970 UTC.

Note: This is different from a UNIX timestamp, which is the number of seconds since the Epoch (Midnight UTC on January 1st, 1970). Even though the representation of a Date is in UTC, the methods to fetch a date or its components work in the host system’s local time zone (which may differ from UTC).

Syntax

const myDate = new Date(dateValue);

The dateValue can be any of the following:

It can be a string representation of a date that is valid and IETF-compliant.
It can be another instance of the Date class.
It can be an integer that represents the date measured in milliseconds since January 1st, 1970 UTC.

The defined range for a Date value is between April 20, 271821 BCE to September 13, 275760 CE. Individual datetime elements can be defined in the Date() constructor with the following syntax:

const d = new Date(year, month, day, hour, minute, second, millisecond);

Date Format Types

In JavaScript, the following three date format types are commonly used:

Format Type	Syntax
ISO Date (The International Standard)	`new Date("YYYY-MM-DDThh:mm:ss.sssZ)`
Short Date	`new Date("YYYY-MM-DD")` / `new Date("YYYY/MM/DD")`
Long Date	`new Date("Mon DD YYYY")` ( or `"DD Month YYYY"`)

With regard to ISO dates:

It is the only format that is strictly enforced while the others may vary in functionality depending on the browser.
“YYYY-MM-DD” or “YYYY/MM/DD” is the preferred format.
In the output, the T separates the date from the time while the Z represents the UTC timezone.
Existing dates can be converted to ISO with the .toISOString() method.

With regard to short dates:

It is best practice to use leading zeros when referring to single-digit calendar days.
If using “YYYY-MM-DD” returns NaN the alternative format “YYYY/MM/DD” should be tested (and vice versa).

With regard to long dates:

The day and month can be in any order.
The month can either be abbreviated (“Mar”) or written in full (“March”).
Names are case-sensitive and commas can be ignored. (e.g. new Date("MONTH DD YYYY"))

Example

When used as a function, Date() returns the current date and time. When used as a constructor, Date() returns a new date object.

const now = Date();
console.log(now);

const then = new Date();
console.log(then);

The output from the snippet above would look similar to this:

Fri Apr 22 2022 17:59:19 GMT+0000 (Coordinated Universal Time)
2022-04-22T17:59:19.244Z

Codebyte Example

The example below defines a new Date object d. Many instance methods are used, which can be found at the bottom of this entry.

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Dates

.getDate(): Returns the day of the month.
.getDay(): Returns the day of the week.
.getFullYear(): Returns the four digit year for the given date.
.getHours(): Returns the hours of a date according to the local time.
.getMilliseconds(): Returns the milliseconds of a date according to the local time.
.getMinutes(): Called from an instance of the Date class, will return the minutes according to the local time.
.getMonth(): Called from an instance of the Date class, will return the month of the year.
.getSeconds(): Called from an instance of the Date class, will return the seconds according to the local time.
.getTime(): Returns the number of milliseconds since the 1st of January 1970.
.getTimezoneOffset(): Returns the time zone offset in minutes between the local time and UTC.
.getUTCDate(): Returns the day of the month for the provided date.
.getUTCDay(): Returns the day of the week in the specified date according to universal time.
.getUTCFullYear(): Returns the year of the specified date according to universal time.
.getUTCHours(): Returns the hours of a provided date according to universal time.
.getUTCMilliseconds(): Returns the milliseconds for a passed date according to universal time.
.getUTCMinutes(): Returns the minutes of the provided date in universal time.
.getUTCMonth(): Returns the month of the specified date according to the UTC zone (0 for January through 11 for December).
.getUTCSeconds(): Returns the seconds (0 to 59) of a date according to universal time.
.now(): Returns the current time in milliseconds. The milliseconds count begins at 1970/01/01 at 00:00:00 UTC.
.setDate(): Changes the day of the month according to local time.
.setFullYear(): Changes the year, month, and/or day according to local time.
.setHours(): Sets the hours for a specified date according to local time.
.setMilliseconds(): Sets the milliseconds of a date.
.setMinutes(): Changes the minute value of a date according to local time.
.setMonth(): Changes the month of a date according to the local time.
.setSeconds(): Sets the seconds component of a date object to a specified value.
.setTime(): Sets the date and time by adding or subtracting a specified number of milliseconds to/from midnight January 1, 1970.
.setUTCDate(): Changes the day of a Date object in Coordinated Universal Time (UTC).
.setUTCFullYear(): Used to set the year value of a Date object in UTC (Coordinated Universal Time).
.setUTCHours(): Sets the hour value of a date object using UTC.
.setUTCMilliseconds(): Sets the milliseconds value of a date object based on Coordinated Universal Time (UTC).
.setUTCMinutes(): Changes the minutes for a given date according to universal time (UTC).
.setUTCMonth(): Sets the month value of a date according to Coordinated Universal Time (UTC).
.setUTCSeconds(): Sets the second value of a date using UTC.
.toDateString(): Returns a string representing the date portion of a Date instance
.toISOString(): Returns a string representation of a date in an ISO 8601-compliant format.
.toJSON(): Returns a string representation of a date in the JavaScript date time string format.
.toLocaleDateString(): Returns a modified string from a given Date object, usually for events. It is translated to a specific language format according to an event locale and other options.
.toLocaleString(): Returns a string formatted based on the locale for a Date object in JavaScript.
.toLocaleTimeString(): Returns a string representing the time portion of a Date object.
.toString(): Converts a Date object to a string.
.toTimeString(): Returns the time portion of the given Date object.
.toUTCString(): Converts a date object to a string, according to UTC.
.UTC(): Returns a number value representing the number of milliseconds between the specified date and January 1, 1970, 00:00:00, Universal Time Coordinated. Will always be called as Date.UTC() rather than called on an instance of date such as myDate.UTC().
.valueOf(): Returns the difference in milliseconds between the specified date and January 1, 1970 00:00:00 UTC.