* 仕様書

[REFS[
- [9] [CITE@en-GB[ECMAScript Language Specification ECMA-262 6th Edition - DRAFT]] ([TIME[2013-03-22 20:28:39 +09:00]] 版) <http://people.mozilla.org/~jorendorff/es6-draft.html#sec-15.9>
- [11] [CITE[Web IDL (Second Edition)]] ([TIME[2013-05-04 05:46:05 +09:00]] 版) <http://dev.w3.org/2006/webapi/WebIDL/#idl-Date>
- [10] '''[CITE[Web IDL (Second Edition)]] ([TIME[2013-05-04 05:46:05 +09:00]] 版) <http://dev.w3.org/2006/webapi/WebIDL/#es-Date>'''
- [14] [CITE@en-US-x-hixie[HTML Standard]] ([TIME[2013-05-05 06:42:10 +09:00]] 版) <http://www.whatwg.org/specs/web-apps/current-work/#create-a-date-object>
]REFS]

* [CODE(JS)@en[new Date]] コンストラクター

@@

* [CODE(JS)@en[Date]] 関数 (JavaScript)

[6] [CODE(JS)@en[[[Date]]]] を[[構築子]]としてではなく[[関数]]として呼ぶと、
[[ES3]] 的には引数で表される[[日時]]の [CODE(JS)@en[[[Date]]]] を文字列化したものが返ってくるはずですが、
[[Firefox]]、[[Chrome]]、[[Opera]]、[[WinIE8]] のいずれも引数を無視して現在日時を表す文字列を返すようです。
[TIME[2010-08-15T23:25:21.100Z]]

;; <javascript:Date(2001,3,5)>

* [CODE(IDL)@en[Date]] 型 (Web IDL)

** 文脈

[13] 
[FIG(list)[
- [CODE(DOMm)@en[getStartDate]] ([CODE(DOMi)@en[HTMLMediaElement]])
- [CODE(DOMa)@en[valueAsDate]] ([CODE(DOMi)@en[HTMLInputElement]])

[HISTORY[
- [CODE(DOMa)@en[startDate]] ([CODE(DOMi)@en[HTMLMediaElement]])
]HISTORY]
]FIG]

** 演算

[15] [DFN[[RUBYB[[CODE(IDL)@en[Date]]オブジェクトを作成]@en[create a [CODE(IDL)@en[Date]] object]]]] [SRC[>>14]]

* 関連

[12] [CODE(DOMi)@en[DOMTimeStamp]]、[CODE(DOMi)@en[DOMHighResTimeStamp]]
のように[[数値]]として[[日時]]を表す[[型][型 (Web IDL)]]もあります。

[REFS[
- [7] [CITE@en[TimezonedDate]]
([[Robin Berjon]] 著, [TIME[2010-04-22 00:10:51 +09:00]] 版)
<http://lists.w3.org/Archives/Public/public-script-coord/2010AprJun/0000.html>
- [16] [CITE@en[Calendar API]] ([TIME[2012-10-02 20:46:33 +09:00]] 版) <http://dev.w3.org/2009/dap/calendar/#calendarevent-interface>
]REFS]

* メモ

[1] [CITE[15.9 Date オブジェクト (Date Objects)]] ([TIME[2002-07-19 22:24:44 +09:00]] 版) <http://www2u.biglobe.ne.jp/~oz-07ams/prog/ecma262r3/15-9_Date_Objects.html>

[4] [CITE[B 互換性 (Compatibility)]] ([TIME[2002-07-19 22:24:55 +09:00]] 版) <http://www2u.biglobe.ne.jp/%7Eoz-07ams/prog/ecma262r3/B_Compatibility.html#section-B.2>

[2] [[閏秒]]には対応していません。
[SRC@en[[[ES3]] 15.9.1.1]]

[3] [CITE[mozilla mozilla/js/src/jsdate.c]] ([TIME[2008-10-28 04:24:06 +09:00]] 版) <http://mxr.mozilla.org/mozilla/source/js/src/jsdate.c>

[5] [CITE@en-us[Date - MDC]] ([TIME[2008-12-14 17:06:41 +09:00]] 版) <https://developer.mozilla.org/ja/Core_JavaScript_1.5_Reference/Global_Objects/Date>

[8] [CITE[''''''[''''''whatwg'''''']'''''' Timing API proposal for measuring intervals]]
( ([TIME[2011-07-14 21:12:44 +09:00]] 版))
<http://lists.whatwg.org/htdig.cgi/whatwg-whatwg.org/2011-July/032343.html>

[17] [CITE@en[Web Applications 1.0 r8094     Revert r8083, since it leads to weird behaviour worse than just returning a new object each time. (It seems this isn't implemented by anyone yet anyway.)]]
( ([TIME[2013-07-27 07:21:00 +09:00]] 版))
<http://html5.org/tools/web-apps-tracker?from=8093&to=8094>

[18] [CITE@en[Web Applications 1.0 r8113     Change startDate to a method to avoid the confusion of it being mutable.]]
( ([TIME[2013-08-01 06:29:00 +09:00]] 版))
<http://html5.org/tools/web-apps-tracker?from=8112&to=8113>

[19] [CITE[IRC logs: freenode / #whatwg / 20130731]]
( ([TIME[2013-08-01 20:10:23 +09:00]] 版))
<http://krijnhoetmer.nl/irc-logs/whatwg/20130731>

[20] [CITE@en[Bug 22824 – Remove Date from WebIDL]]
( ([TIME[2013-08-19 07:24:31 +09:00]] 版))
<https://www.w3.org/Bugs/Public/show_bug.cgi?id=22824>

[21] [CITE[Java8日付時刻APIの使いづらさと凄さ - きしだのはてな]]
( ([TIME[2013-09-17 06:57:18 +09:00]] 版))
<http://d.hatena.ne.jp/nowokay/20130917#1379376320>

[22] [CITE@en[File API | lastModified and Date attribute change]]
( ([[Arun Ranganathan]] 著, [TIME[2013-12-03 07:26:07 +09:00]] 版))
<http://lists.w3.org/Archives/Public/public-webapps/2013OctDec/0662.html>

[23] [CITE[HTML date format and Date.parse()]]
( ([TIME[2013-04-30 23:15:56 +09:00]] 版))
<https://mail.mozilla.org/pipermail/es-discuss/2013-April/030412.html>

[24] [CITE@en[Emotion Markup Language (EmotionML) 1.0]]
( ([TIME[2014-05-20 20:02:30 +09:00]] 版))
<http://www.w3.org/TR/emotionml/#s2.4.2.1>

[25] [CITE@en[RFC 3507 - Internet Content Adaptation Protocol (ICAP)]]
( ([TIME[2014-06-08 07:17:07 +09:00]] 版))
<http://tools.ietf.org/html/rfc3507#section-4.3.1>

[26] [CITE@en[Merge pull request #342 from martinthomson/issue324 · w3c/webrtc-pc@05909f7]]
([TIME[2015-10-24 13:20:07 +09:00]] 版)
<https://github.com/w3c/webrtc-pc/commit/05909f7d33c0dca829816c3ca47b93a593fb9fc6>

[27] [CITE@en[Close #279: stop using IDL Date so it can be removed from IDL · whatwg/html@260b66f]]
([TIME[2015-10-26 11:40:59 +09:00]] 版)
<https://github.com/whatwg/html/commit/260b66f352b34143c29bf3b2f5a17f9b5c34c1e1>

[28] [CITE@en[22824 – Remove Date from WebIDL]]
([TIME[2015-10-27 12:58:07 +09:00]] 版)
<https://www.w3.org/Bugs/Public/show_bug.cgi?id=22824>

[29] [CITE@en[Breaking: refactor structured clone into serialize/deserialize]]
([[domenic]]著, [TIME[2017-03-21 06:09:33 +09:00]])
<https://github.com/whatwg/html/commit/97d644c97335956610a31e8ad98d1a388c063e84>

[30] [CITE@en[API Reference - Web Application - Tizen Web Device API Reference - System - Time API | Tizen Developers]]
([TIME[2017-04-13 01:21:29 +09:00]])
<https://developer.tizen.org/development/api-references/web-application?redirect=https://developer.tizen.org/dev-guide/3.0.0/org.tizen.web.apireference/html/device_api/mobile/tizen/time.html>

[FIG(quote)[
[FIGCAPTION[
[31] [CITE[Safari には、1970年以前のDateが西半球で1ミリ秒ずれるバグがある - Qiita]]
([TIME[2017-12-02 13:07:23 +09:00]])
<https://qiita.com/kawanet/items/b081030911a12531561a>
]FIGCAPTION]

> new Date("1969-12-31T23:59:59.999+01:00").toJSON();
> // OK! => "1969-12-31T22:59:59.999Z"
> new Date("1969-12-31T23:59:59.999-01:00").toJSON();
> // NG! => "1970-01-01T00:59:59.998Z"

]FIG]


[32] [CITE@en["object getStartDate()" should be "Date getStartDate()" · Issue #3340 · whatwg/html]]
([TIME[2018-01-17 15:56:25 +09:00]])
<https://github.com/whatwg/html/issues/3340>

[33] [CITE[ECMAScript® 2020 Language Specification]]
([TIME[2019-03-02 01:48:00 +09:00]])
<https://tc39.github.io/ecma262/#sec-date-constructor>

[34] [CITE@ja[Dateオブジェクト (日付と時刻) | JavaScript プログラミング解説]]
([TIME[2019-05-11 06:04:33 +09:00]])
<https://so-zou.jp/web-app/tech/programming/javascript/grammar/object/date.htm>

[35] 
[CITE@en[Normative: explicitly specify order of operations in MakeTime by bakkot · Pull Request #2120 · tc39/ecma262 · GitHub]], [TIME[2023-11-13T03:34:00.000Z]] <https://github.com/tc39/ecma262/pull/2120>

[36] 
[CITE@ja[Dates and IEEE754 - Google スライド]], [TIME[2023-11-13T03:36:56.000Z]] <https://docs.google.com/presentation/d/1gePsNmlP2u0pYXm0LWO3d7eM4Q_y5Ozx0qXN1zWOv58/edit#slide=id.g106f4536d9_0_109>