JS: Date.prototype

By Xah Lee. Date: 2016-12-10. Last updated: 2024-04-09.

What is Date.prototype

Date.prototype is the value of the property key "prototype" of the function Date. 〔see Date Object〕

Date.hasOwnProperty ( "prototype" )

Type

Type of Date.prototype is Object .

typeof Date.prototype === "object"

Parent

Parent of Date.prototype is Object.prototype .

Reflect.getPrototypeOf ( Date.prototype ) === Object.prototype

Purpose

Date.prototype is the parent of all date instances.

Reflect.getPrototypeOf ( new Date() ) === Date.prototype

Purpose of Date.prototype is to provide methods and properties useful for all date instances.

Properties

Get

Most date get/set methods have 2 versions. One returns local time info, one returns UTC time info. e.g. getHours() vs getUTCHours().

getTime(): Return the millisecond representation of a Date object. Sample: 1428605303481.
getFullYear(), getUTCFullYear(): Year of the date. 4 digits. e.g. 2014.
getYear(): Return the year minus 1901. Deprecated. Use getFullYear().
getMonth(), getUTCMonth(): Month. 0 to 11. January is 0. February is 1. December is 11.
getDate(), getUTCDate(): Day of the month. 1 to 31.
getDay(), getUTCDay(): Day of the week. 0 to 6. Sunday is 0. Monday is 1. Saturday is 6.
getHours(), getUTCHours(): Hours. 0 to 23.
getMinutes(), getUTCMinutes(): Minutes. 0 to 59.
getSeconds(), getUTCSeconds(): Seconds. 0 to 59.
getMilliseconds(), getUTCMilliseconds(): Milliseconds field of a Date object. 0 to 999.
getTimezoneOffset(): Difference, in minutes, between the local and UTC time of this date. Daylight saving time is taken account of.

Set

setTime(milliseconds): Set the date object to a specific datetime of milliseconds, the internal date format.
setFullYear(year, month, date), setUTCFullYear(…): Set the year to year. The other parameters are optional.
setYear(year): Set the year to year. Deprecated. Use setFullYear().
setMonth(month, date), setUTCMonth(…): Set the month to month. Note, January is 0. Other parameters are optional.
setDate(date), setUTCDate(…): Set the date part to date.
setHours(hour, min, sec, millisecond), setUTCHours(…): Set the hour to hour. The rest parameters are optional.
setMinutes(min, sec, millisecond), setUTCMinutes(…): Set the minutes to min. The rest parameters are optional.
setSeconds(sec, millisecond), setUTCSeconds(…): Set the second sec. The rest parameters are optional.
setMilliseconds(ms), setUTCMilliseconds(…): Set the milliseconds part of a date to ms.

Print

toLocaleString(): Return a string that is the complete date info in human readable form of the local time zone, and in a format of local convention. Sample:
"Sat Apr 08 2017 08:48:22 GMT-0700 (PDT)"
toLocaleDateString(): Same as toLocaleString(), but return only the date part. Sample:
"Sat Apr 08 2017"
toLocaleTimeString(): Same as toLocaleString(), but return only the time part. Sample:
"08:48:22 GMT-0700 (PDT)"
toDateString(): Return a string that is the date part in human readable form of the local time zone. Sample:
"Wed Apr 08 2015"
toTimeString(): Return a string that is the time part in human readable form of the local time zone. Sample:
"08:48:22 GMT-0700 (PDT)"
toISOString(): Return a string that is ISO-8601 format in UTC timezone. Sample:
"2015-04-08T15:48:22.000Z"
toUTCString(): Return human readable format in UTC timezone. Return string format is implementation dependent. Sample:
"Wed, 08 Apr 2015 15:48:22 GMT"
toGMTString(): Return a string using the GMT time zone. Deprecated. Use toUTCString() instead. Sample:
"Wed, 08 Apr 2015 15:48:22 GMT"
toJSON(): Return a JSON representation of Date object, using toISOString(). Sample:
"2015-04-08T15:48:22.000Z"
toString(): Return date time in string format. Sample:
"Wed Apr 08 2015 08:48:22 GMT-0700 (PDT)"
valueOf(): Return the millisecond representation of a date time. Sample:
1428605303481. Same as getTime()

Misc

Date.prototype.constructor: Value is Date. 〔see Date Object〕
Date.prototype[Symbol.toPrimitive] (new in JS: ECMAScript 2015)

Difference between UTC and GMT

For practical purposes, they are the same.

UTC (Coordinated Universal Time) is a time standard based on atomic clock.

GMT (Greenwich Mean Time) is a older time standard.

“Zulu time” is a term used in military and is the same as GMT. (GMT and UTC has an abbrev of Z, because Z mean zero, for zero offset. Z in NATO phonetic alphabet is read as Zulu. That's why GMT/UTC is sometimes said “Zulu time”.)