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      • Intl Locale Info S4

      Proposal details
      Proposal overview

      This proposal adds methods to Intl.Locale to expose locale-specific information, including week data (first day, weekend), text direction, and defaults for calendars, collations, hour cycles, numbering systems, and time zones.

      Note

      The README below comes from the upstream repository and may contain outdated stage or status metadata. Use the proposal details above as the current source of truth.

      Intl Locale Info API

      This proposal is fully adopted into the ECMA-402, 13th edition, June 2026 "ECMAScript® 2026 internationalization API specification"

      Draft Spec

      https://tc39.github.io/proposal-intl-locale-info

      Stage

      Stage 4

      Entrance Criteria for Stage 1 (Proposal)

      • Identified “champion” who will advance the addition: Frank Yung-Fong Tang
      • Prose outlining the problem or need and the general shape of a solution: See this document
      • Illustrative examples of usage: See this document
      • High-level API: See this document
      • Discussion of key algorithms, abstractions and semantics
      • Identification of potential “cross-cutting” concerns and implementation challenges/complexity
      • A publicly available repository for the proposal that captures the above requirements:

      Entrance Criteria for Stage 2 (Draft)

      • Above
      • Initial spec text: DONE
      • Acceptance Signifies: The committee expects the feature to be developed and eventually included in the standard

      Entrance Criteria for Stage 3 (Candidate)

      • Above
      • Complete spec text
      • Designated reviewers have signed off on the current spec text
      • All ECMAScript editors have signed off on the current spec text
      • Acceptance Signifies: The solution is complete and no further work is possible without implementation experience, significant usage and external feedback.

      Champion

      • Frank Tang @FrankYFTang

      Designated reviewers

      • Shane Carr @sffc
      • Zibi Braniecki @zbraniecki

      ECMAScript editors

      • Richard Gibson @gibson042

      Implementation Status

      • V8 (UPDATE 2021-5-6:) : Behind a flag (cl/2570218 is landed into the trunk)
        • $ out/x64.release/d8 --harmony_intl_locale_info
        • Chrome - TBD
        • Edge - ???
      • FireFox - Tracking Bug
      • Safari - ???

      Scope

      A proposal to expose Locale information, such as week data (first day in a week, weekend start day, weekend end day), and text direction hour cycle used in the locale ,measurement system used in the locale.

      Motivation / Use Case

      Locale Information is necessary for many low level operations.

      • Direction in textInfo will be needed for layout, and for localization information (bidi boundaries with placeholders etc.)
      • WeekInfo will be needed for calendar widgets and applications to display correct monthly and weekly views.

      High Level Design

      Add methods to Intl to get object to contains group of information:

      Week Data
      let he = new Intl.Locale("he")
he.getWeekInfo()
// {firstDay: 7, weekend: [5, 6]}
let af = new Intl.Locale("af")
af.getWeekInfo()
// {firstDay: 7, weekend: [6, 7]}
enGB = new Intl.Locale("en-GB")
enGB.getWeekInfo()
// {firstDay: 1, weekend: [6, 7]}

let msBN = new Intl.Locale("ms-BN")
msBN.getWeekInfo()
// {firstDay: 7, weekend: [5, 7]}  // Brunei weekend is Friday and Sunday but not Saturday

      Monday is 1 and Sunday is 7, as defined by ISO-8861 and followed by Temporal proposal

      Text Information
      l = new Intl.Locale("ar")
let ti = l.getTextInfo();
// { direction: "rtl" }
ti.direction
// rtl
      Defaults
      ~/v8/v8$ out/x64.release/d8 --harmony_intl_locale_info
V8 version 9.1.0 (candidate)
d8> ar = new Intl.Locale("ar")
ar
d8> ar.getCalendars()
["gregory", "coptic", "islamic", "islamic-civil", "islamic-tbla"]
d8> ar.getCollations()
["compat", "emoji", "eor"]
d8> ar.getHourCycles()
["h12"]
d8> ar.getNumberingSystems()
["latn"]
d8> ar.getTimeZones()
undefined

d8> arEG = new Intl.Locale("ar-EG")
ar-EG
d8> arEG.getCalendars()
["gregory", "coptic", "islamic", "islamic-civil", "islamic-tbla"]
d8> arEG.getCollations()
["compat", "emoji", "eor"]
d8> arEG.getHourCycles()
["h12"]
d8> arEG.getNumberingSystems()
["arab"]
d8> arEG.getTimeZones()
["Africa/Cairo"]

d8> arSA = new Intl.Locale("ar-SA")
ar-SA
d8> arSA.getCalendars()
["islamic-umalqura", "gregory", "islamic", "islamic-rgsa"]
d8> arSA.getCollations()
["compat", "emoji", "eor"]
d8> arSA.getHourCycles()
["h12"]
d8> arSA.getNumberingSystems()
["arab"]
d8> arSA.getTimeZones()
timeZones: ["Asia/Riyadh"]

d8> ja = new Intl.Locale("ja")
ja
d8> ja.getCalendars()
["gregory", "japanese"]
d8> ja.getCollations()
["unihan", "emoji", "eor"]
d8> ja.getHourCycles()
["h23"]
d8> ja.getNumberingSystems()
["latn"]
d8> ja.getTimeZones()
undefined

d8> jaJP = new Intl.Locale("ja-JP")
ja-JP
d8> jaJP.getCalendars()
["gregory", "japanese"]
d8> jaJP.getCollations()
["unihan", "emoji", "eor"]
d8> jaJP.getHourCycles()
["h23"]
d8> jaJP.getNumberingSystems()
["latn"]
d8> jaJP.getTimeZones()
["Asia/Tokyo"]}

d8> enUS = new Intl.Locale("en-US")
en-US
d8> enUS.getCalendars()
["gregory"]
d8> enUS.getCollations()
["emoji", "eor"]
d8> enUS.getHourCycles()
["h12"]
d8> enUS.getNumberingSystems()
["latn"]
d8> enUS.getTimeZones()
["America/Adak", "America/Anchorage", "America/Boise", "America/Chicago", "America/Denver", "America/Detroit", "America/Indiana/Knox", "America/Indiana/Marengo", "America/Indiana/Petersburg", "America/Indiana/Tell_City", "America/Indiana/Vevay", "America/Indiana/Vincennes", "America/Indiana/Winamac", "America/Indianapolis", "America/Juneau", "America/Kentucky/Monticello", "America/Los_Angeles", "America/Louisville", "America/Menominee", "America/Metlakatla", "America/New_York", "America/Nome", "America/North_Dakota/Beulah", "America/North_Dakota/Center", "America/North_Dakota/New_Salem", "America/Phoenix", "America/Sitka", "America/Yakutat", "Pacific/Honolulu"]

d8> enNZ = new Intl.Locale("en-NZ")
en-NZ
d8> enNZ.getCalendars()
["gregory"]
d8> enNZ.getCollations()
["emoji", "eor"]
d8> enNZ.getHourCycles()
["h12"]
d8> enNZ.getNumberingSystems()
["latn"]
d8> enNZ.getTimeZones()
["Pacific/Auckland", "Pacific/Chatham"]

d8> zh = new Intl.Locale("zh")
zh
d8> zh.getCalendars()
["gregory", "chinese"]
d8> zh.getCollations()
["pinyin", "big5han", "gb2312han", "stroke", "unihan", "zhuyin", "emoji", "eor"]
d8> zh.getHourCycles()
["h12"]
d8> zh.getNumberingSystems()
["latn"]
d8> zh.getTimeZones()
undefined

d8> zhTW = new Intl.Locale("zh-TW")      
zh-TW
d8>  zhTW.getCalendars()
["gregory", "roc", "chinese"]
d8>  zhTW.getCollations()
["stroke", "big5han", "gb2312han", "pinyin", "unihan", "zhuyin", "emoji", "eor"]
d8>  zhTW.getHourCycles()
["h12"]
d8>  zhTW.getNumberingSystems()
["latn"]
d8>  zhTW.getTimeZones()
["Asia/Taipei"]

d8> zhHK = new Intl.Locale("zh-HK")
zh-HK
d8> zhHK.getCalendars()
["gregory", "chinese"]
d8> zhHK.getCollations()
["stroke", "big5han", "gb2312han", "pinyin", "unihan", "zhuyin", "emoji", "eor"]
d8> zhHK.getHourCycles()
["h12"]
d8> zhHK.getNumberingSystems()
["latn"]
d8> zhHK.getTimeZones()
["Asia/Hong_Kong"]

d8> fa = new Intl.Locale("fa")
fa
d8> fa.getCalendars()
["persian", "gregory", "islamic", "islamic-civil", "islamic-tbla"]
d8> fa.getCollations()
["emoji", "eor"]
d8> fa.getHourCycles()
["h23"]
d8> fa.getNumberingSystems()
["arabext"]
d8> fa.getTimeZones()
undefined
      Unit Information DROPPED FEATURE
      l = new Intl.Locale("ar")
let unitInfo = l.unitInfo;
// {measurementSystem: "metric"}
l.unitInfo.measurementSystem
// metric
l = new Intl.Locale("en-GB")
l.unitInfo
// {measurementSystem: "uksystem"}
l = new Intl.Locale("en-GB")
l.unitInfo
// {measurementSystem: "uksystem"}
l = new Intl.Locale("en")
l.unitInfo
// {measurementSystem: "ussystem"}

      Polyfills

      PolyfillRepo
      @bart-krakowski/get-week-info-polyfill@bart-krakowski/get-week-info-polyfill