Draft ECMA-402 / October 22, 2025

ECMAScript® 2026 Internationalization API Specification

Contributing to this Specification

This specification is developed on GitHub with the help of the ECMAScript community. There are a number of ways to contribute to the development of this specification:

Refer to the colophon for more information on how this document is created.

Introduction

This specification's source can be found at https://github.com/tc39/ecma402.

The ECMAScript 2026 Internationalization API Specification (ECMA-402 13th Edition), provides key language sensitive functionality as a complement to ECMA-262. Its functionality has been selected from that of well-established internationalization APIs such as those of the Internationalization Components for Unicode (ICU) library (

1 Scope

This Standard defines the application programming interface for ECMAScript objects that support programs that need to adapt to the linguistic and cultural conventions used by different human languages and countries.

2 Conformance

A conforming implementation of this specification must conform to ECMA-262, and must provide and support all the objects, properties, functions, and program semantics described in this specification. Nothing in this specification is intended to allow behaviour that is otherwise prohibited by ECMA-262, and any such conflict should be considered an editorial error rather than an override of constraints from ECMA-262.

A conforming implementation is permitted to provide additional objects, properties, and functions beyond those described in this specification. In particular, a conforming implementation is permitted to provide properties not described in this specification, and values for those properties, for objects that are described herein. A conforming implementation is not permitted to add optional arguments to the functions defined in this specification.

A conforming implementation is permitted to accept additional values, and then have implementation-defined behaviour instead of throwing a RangeError, for the following properties of options arguments:

3 Normative References

The following referenced documents are required for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

ECMAScript 2026 Language Specification (ECMA-262 17th Edition, or successor).
https://www.ecma-international.org/publications/standards/Ecma-262.htm

Note
Sections of this specification that depend on these references are updated on a best-effort basis, but are not guaranteed to be up-to-date with those standards.

4 Overview

This section is non-normative.

4.1 Internationalization, Localization, and Globalization

Internationalization of software means designing it such that it supports or can be easily adapted to support the needs of users speaking different languages and having different cultural expectations, and enables worldwide communication between them. Localization then is the actual adaptation to a specific language and culture. Globalization of software is commonly understood to be the combination of internationalization and localization. Globalization starts at the lowest level by using a text representation that supports all languages in the world, and using standard identifiers to identify languages, countries, time zones, and other relevant parameters. It continues with using a user interface language and data presentation that the user understands, and finally often requires product-specific adaptations to the user's language, culture, and environment.

ECMA-262 lays the foundation by using Unicode for text representation and by providing a few language-sensitive functions, but gives applications little control over the behaviour of these functions. This specification builds on that foundation by providing a set of customizable language-sensitive functionality. The API is useful even for applications that themselves are not internationalized, as even applications targeting only one language and one region need to properly support that one language and region. However, the API also enables applications that support multiple languages and regions, even concurrently, as may be needed in server environments.

4.2 API Overview

This specification is designed to complement ECMA-262 by providing key language-sensitive functionality, and can be added to an implementation thereof in whole or in part. This specification introduces new language values observable to ECMAScript code (such as the value of a [[FallbackSymbol]] internal slot and the set of values transitively reachable from %Intl% by property access), and also refines the definition of some functions specified in ECMA-262 (as described below). Neither category prohibits behaviour that is otherwise permitted for values and interfaces defined in ECMA-262, in order to support adoption of this specification by any implementation.

This specification provides several key pieces of language-sensitive functionality that are required in most applications: locale selection and inspection, string comparison (collation) and case conversion, pluralization rules, text segmentation, and formatting of numbers, absolute and relative dates and times, durations, and lists. While ECMA-262 provides functions for this basic functionality (on Date.prototype: toLocaleString, toLocaleDateString, and toLocaleTimeString), their actual behaviour is left largely implemenation-defined. This specification provides additional functionality, control over the language and over details of the behaviour to be used, and a more complete specification of required functionality.

Applications can use the API in two ways:

  1. Directly, by using a service constructor to construct an object, specifying a list of preferred languages and options to configure its behaviour. The object provides a main function (compare, select, format, etc.), which can be called repeatedly. It also provides a resolvedOptions function, which the application can use to find out the exact configuration of the object.
  2. Indirectly, by using the functions of ECMA-262 mentioned above. The collation and formatting functions are respecified in this specification to accept the same arguments as the Collator, NumberFormat, and DateTimeFormat constructors and produce the same results as their compare or format methods. The case conversion functions are respecified to accept a list of preferred languages.

The Intl object is used to package all functionality defined in this specification in order to avoid name collisions.

Note
While the API includes a variety of formatters, it does not provide any parsing facilities. This is intentional, has been discussed extensively, and concluded after weighing in all the benefits and drawbacks of including said functionality. See the discussion on the issue tracker.

4.3 API Conventions

Every Intl constructor should behave as if defined by a class, throwing a TypeError exception when called as a function (without NewTarget). For backwards compatibility with past editions, this does not apply to %Intl.Collator%, %Intl.DateTimeFormat%, or %Intl.NumberFormat%, each of which construct and return a new object when called as a function.

Note
In ECMA 402 v1, Intl Issue 57 for details.

4.4 Implementation Dependencies

Due to the nature of internationalization, this specification has to leave several details implementation dependent:

  • The set of locales that an implementation supports with adequate localizations: Linguists have described thousands of human languages, with the IANA Language Subtag Registry containing over 7000 primary language subtags (used as the base for locale identifiers). Even large locale data collections, such as the Common Locale Data Repository, cover only a tiny subset of all languages and their regional or dialectical variations. Implementations targeting resource-constrained devices may have to further reduce the subset.
  • The exact form of localizations such as format patterns: In many cases locale-dependent conventions are not standardized, so different forms may exist side by side, or they vary over time. Different internationalization libraries may have implemented different forms, without any of them being actually wrong. In order to allow this API to be implemented on top of existing libraries, such variations have to be permitted.
  • Subsets of Unicode: Some operations, such as collation, operate on strings that can include characters from the entire Unicode character set. However, both the Unicode Standard and the ECMAScript standard allow implementations to limit their functionality to subsets of the Unicode character set. In addition, locale conventions typically don't specify the desired behaviour for the entire Unicode character set, but only for those characters that are relevant for the locale. While the Unicode Collation Algorithm combines a default collation order for the entire Unicode character set with the ability to tailor for local conventions, subsets and tailorings still result in differences in behaviour.

In browser implementations the initial set of locales, currencies, calendars, numbering systems, and other enumerable items visible to a particular origin must be the same for all users sharing the same user agent string (engine and platform version). Furthermore, dynamic changes to these sets must not result in users becoming distinguishable from each other. This constraint is imposed to reduce the fingerprinting risk inherent in internationalization, and may be relaxed in future revisions. As a result of this constraint, the first time a browser implementation that allows on-demand locale installation receives a request from a particular origin that could require installing a new locale, it must not reveal whether or not that locale is already installed.

Throughout this specification, implementation- and locale-dependent behaviour is referred to as ILD, and implementation-, locale-, and numbering system-dependent behaviour is referred to as ILND.

4.4.1 Compatibility across implementations

ECMA 402 describes the schema of the data used by its functions. The data contained inside is implementation-dependent, and expected to change over time and vary between implementations. The variation is visible by programmers, and it is possible to construct programs which will depend on a particular output. However, this specification attempts to describe reasonable constraints which will allow well-written programs to function across implementations. Implementations are encouraged to continue their efforts to harmonize linguistic data.

5 Notational Conventions

This standard uses a subset of the notational conventions of ECMA-262:

Note
As described in ECMA-262, algorithms are used to precisely specify the required semantics of ECMAScript constructs, but are not intended to imply the use of any specific implementation technique. Internal slots are used to define the semantics of object values, but are not part of the API. They are defined purely for expository purposes. An implementation of the API must behave as if it produced and operated upon internal slots in the manner described here.

As an extension to the Record Specification Type, the notation “[[<name>]]” denotes a field whose name is given by the variable name, which must have a String value. For example, if a variable s has the value "a", then [[<s>]] denotes the field [[a]].

This specification uses blocks demarcated as host is not a web browser.

5.1 Well-Known Intrinsic Objects

The following table extends the Well-Known Intrinsic Objects table defined in Well-Known Intrinsic Objects.

Table 1: Well-known Intrinsic Objects (Extensions)
Intrinsic Name Global Name ECMAScript Language Association
%Intl% Intl The Intl object (8)
%Intl.Collator% Intl.Collator The Intl.Collator constructor (10.1)
%Intl.DateTimeFormat% Intl.DateTimeFormat The Intl.DateTimeFormat constructor (11.1)
%Intl.DisplayNames% Intl.DisplayNames The Intl.DisplayNames constructor (12.1)
%Intl.DurationFormat% Intl.DurationFormat The Intl.DurationFormat constructor (13.1)
%Intl.ListFormat% Intl.ListFormat The Intl.ListFormat constructor (14.1)
%Intl.Locale% Intl.Locale The Intl.Locale constructor (15.1)
%Intl.NumberFormat% Intl.NumberFormat The Intl.NumberFormat constructor (16.1)
%Intl.PluralRules% Intl.PluralRules The Intl.PluralRules constructor (17.1)
%Intl.RelativeTimeFormat% Intl.RelativeTimeFormat The Intl.RelativeTimeFormat constructor (18.1)
%Intl.Segmenter% Intl.Segmenter The Intl.Segmenter constructor (19.1)
%IntlSegmentIteratorPrototype% The prototype of Segment Iterator objects (19.6.2)
%IntlSegmentsPrototype% The prototype of Segments objects (19.5.2)

6 Identification of Locales, Currencies, Time Zones, Measurement Units, Numbering Systems, Collations, and Calendars

This clause describes the String values used in this specification to identify locales, currencies, time zones, measurement units, numbering systems, collations, calendars, and pattern strings.

6.1 Case Sensitivity and Case Mapping

The String values used to identify locales, currencies, scripts, and time zones are interpreted in an ASCII-case-insensitive manner, treating the code units 0x0041 through 0x005A (corresponding to Unicode characters LATIN CAPITAL LETTER A through LATIN CAPITAL LETTER Z) as equivalent to the corresponding code units 0x0061 through 0x007A (corresponding to Unicode characters LATIN SMALL LETTER A through LATIN SMALL LETTER Z), both inclusive. No other case folding equivalences are applied.

Note
For example, "ß" (U+00DF) must not match or be mapped to "SS" (U+0053, U+0053). "ı" (U+0131) must not match or be mapped to "I" (U+0049).

The ASCII-uppercase of a String value S is the String value derived from S by replacing each occurrence of an ASCII lowercase letter code unit (0x0061 through 0x007A, inclusive) with the corresponding ASCII uppercase letter code unit (0x0041 through 0x005A, inclusive) while preserving all other code units.

The ASCII-lowercase of a String value S is the String value derived from S by replacing each occurrence of an ASCII uppercase letter code unit (0x0041 through 0x005A, inclusive) with the corresponding ASCII lowercase letter code unit (0x0061 through 0x007A, inclusive) while preserving all other code units.

A String value A is an ASCII-case-insensitive match for String value B if the ASCII-uppercase of A is exactly the same sequence of code units as the ASCII-uppercase of B. A sequence of Unicode code points A is an ASCII-case-insensitive match for B if B is an ASCII-case-insensitive match for CodePointsToString(A).

6.2 Language Tags

This specification identifies locales using Unicode BCP 47 locale identifiers as defined by Section 3 Unicode Language and Locale Identifiers. Each such identifier can also be referred to as a language tag, and is in fact a valid language tag as that term is used in BCP 47. A locale identifier in canonical form as specified in Unicode Technical Standard #35 Part 1 Core, Section 3.2.1 Canonical Unicode Locale Identifiers is referred to as a "Unicode canonicalized locale identifier".

Locale identifiers consist of case-insensitive Unicode Basic Latin alphanumeric subtags separated by "-" (U+002D HYPHEN-MINUS) characters, with single-character subtags referred to as "singleton subtags". Unicode Technical Standard #35 Part 1 Core, Section 3.6 Unicode BCP 47 U Extension subtag sequences are used extensively, and the term "Unicode locale extension sequence" describes the longest substring of a language tag that can be matched by the unicode_locale_extensions Unicode locale nonterminal and is not part of a "-x-…" private use subtag sequence. It starts with "-u-" and includes all immediately following subtags that are not singleton subtags, along with their preceding "-" separators. For example, the Unicode locale extension sequence of "en-US-u-fw-mon-x-u-ex-foobar" is "-u-fw-mon".

All structurally valid language tags are appropriate for use with the APIs defined by this specification, but implementations are not required to use Unicode Common Locale Data Repository (implementation-defined. Intl constructors map requested language tags to locales supported by their respective implementations.

6.2.1 IsStructurallyValidLanguageTag ( locale )

The abstract operation IsStructurallyValidLanguageTag takes argument locale (a String) and returns a Boolean. It determines whether locale is a syntactically well-formed language tag. It does not consider whether locale conveys any meaningful semantics, nor does it differentiate between aliased subtags and their preferred replacement subtags or require canonical casing or subtag ordering. It performs the following steps when called:

  1. Let lowerLocale be the ASCII-lowercase of locale.
  2. If lowerLocale cannot be matched by the unicode_locale_id Unicode locale nonterminal, return false.
  3. If lowerLocale uses any of the backwards compatibility syntax described in Assert: The substring of transformExtension from 3.
  4. Let tlang be the longest prefix of tPrefix matched by the tlang Unicode locale nonterminal. If there is no such prefix, return true.
  5. Let tlangVariants be GetLocaleVariants(tlang).
  6. If tlangVariants contains any duplicate subtags, return false.
  • Return true.
    •

    6.2.2 CanonicalizeUnicodeLocaleId ( locale )

    The abstract operation CanonicalizeUnicodeLocaleId takes argument locale (a language tag) and returns a Unicode canonicalized locale identifier. It returns the canonical and case-regularized form of locale. It performs the following steps when called:

    1. Let localeId be the String value resulting from performing the algorithm to transform locale to canonical form per string-concatenation of newExtension, "-", and keyword.[[Key]].
    2. If keyword.[[Value]] is not the empty String, then
      1. Set newExtension to the Assert: newExtension is not "-u".
      2. Set localeId to a copy of localeId in which the first appearance of substring extension has been replaced with newExtension.
    3. Return localeId.
     Note
    Step 2 ensures that a Unicode locale extension sequence in the returned language tag contains:
    • only the first instance of any attribute duplicated in the input, and
    • only the first keyword for a given key in the input.

    6.2.3 DefaultLocale ( )

    The host environment's current locale. It must not contain a Unicode locale extension sequence.

    Note
    The returned value is is a potential fingerprinting vector. In browser environments, it should match navigator.language to avoid providing any additional distinguishing information.

    6.3 Currency Codes

    This specification identifies currencies using 3-letter currency codes as defined by ISO 4217. Their canonical form is uppercase.

    All well-formed 3-letter ISO 4217 currency codes are allowed. However, the set of combinations of currency code and language tag for which localized currency symbols are available is implementation dependent. Where a localized currency symbol is not available, the ISO 4217 currency code is used for formatting.

    6.3.1 IsWellFormedCurrencyCode ( currency )

    The abstract operation IsWellFormedCurrencyCode takes argument currency (a String) and returns a Boolean. It verifies that the currency argument represents a well-formed 3-letter ISO 4217 currency code. It performs the following steps when called:

    1. If the length of currency is not 3, return false.
    2. Let normalized be the ASCII-uppercase of currency.
    3. If normalized contains any code unit outside of 0x0041 through 0x005A (corresponding to Unicode characters LATIN CAPITAL LETTER A through LATIN CAPITAL LETTER Z), return false.
    4. Return true.

    6.4 AvailableCanonicalCurrencies ( )

    The lexicographic code unit order, and contains unique, well-formed, and upper case canonicalized 3-letter ISO 4217 currency codes, identifying the currencies for which the implementation provides the functionality of Intl.DisplayNames and Intl.NumberFormat objects.

    6.5 Use of the IANA Time Zone Database

    Implementations that adopt this specification must be available named time zone identifiers and data used in ECMAScript calculations and formatting. This section defines how the IANA Time Zone Database should be used by time zone aware implementations. No String may be an available named time zone identifier unless it is a Zone name or a Link name in the IANA Time Zone Database. Available named time zone identifiers returned by ECMAScript built-in objects must use the casing found in the IANA Time Zone Database.

    Each Zone in the IANA Time Zone Database must be a non-primary time zone identifier that resolves to its corresponding Zone name, with the following exceptions implemented in AvailableNamedTimeZoneIdentifiers:

    • For historical reasons, "UTC" must be a primary time zone identifier. "Etc/UTC", "Etc/GMT", and "GMT", as well as all Link names that resolve to any of them, must be non-primary time identifiers that resolve to "UTC".
    • Any Link name that is present in the “TZ” column of file zone.tab must be a primary time zone identifier. For example, both "Europe/Prague" and "Europe/Bratislava" must be primary time zone identifiers. This requirement guarantees at least one ISO 3166-1 Alpha-2 country code, and ensures that future changes to time zone rules of one country will not affect ECMAScript programs that use another country's time zone(s), unless those countries' territorial boundaries have also changed.
    • Any Link name that is not listed in the “TZ” column of file zone.tab and that represents a geographical area entirely contained within the territory of a single ISO 3166-1 Alpha-2 country code must resolve to a primary identifier that also represents a geographical area entirely contained within the territory of the same country code. For example, "Atlantic/Jan_Mayen" must resolve to "Arctic/Longyearbyen".
    Note

    The IANA Time Zone Database offers build options that affect which available named time zone identifiers are primary. The default build options merge different countries' time zones, for example "Atlantic/Reykjavik" is built as a Link to the Zone "Africa/Abidjan". Geographically and politically distinct locations are likely to introduce divergent time zone rules in a future version of the IANA Time Zone Database. The exceptions above serve to mitigate these future-compatibility issues.

    The Unicode Common Locale Data Repository (available named time zone identifiers are primary or non-primary. Although use of CLDR data is recommended for consistency between implementations, it is not required. Non-CLDR-based implementations can still use CLDR's identifier data in timezone.xml. Implementations may also build the IANA Time Zone Database directly, for example by using build options such as PACKRATDATA=backzone PACKRATLIST=zone.tab and performing any post-processing needed to ensure compliance with the requirements above.

    The IANA Time Zone Database is typically updated between five and ten times per year. These updates may add new Zone or Link names, may change Zones to Links, and may change the UTC offsets and transitions associated with any Zone. Implementations are recommended to include updates to the IANA Time Zone Database as soon as possible. Such prompt action ensures that ECMAScript programs can accurately perform time-zone-sensitive calculations and can use newly-added host environment.

    Although the IANA Time Zone Database maintainers strive for stability, in rare cases (averaging less than once per year) a Zone may be replaced by a new Zone. For example, in 2022 "Europe/Kiev" was deprecated to a Link resolving to a new "Europe/Kyiv" Zone. The deprecated Link is called a renamed time zone identifier and the newly-added Zone is called a replacement time zone identifier.

    To reduce disruption from these infrequent changes, implementations should initially add each replacement time zone identifier as a non-primary time zone identifier that resolves to the existing renamed time zone identifier. This allows ECMAScript programs to recognize both identifiers, but also reduces the chance that an ECMAScript program will send the replacement time zone identifier to another system that does not yet recognize it. After a rename waiting period, implementations should promote the new Zone to a primary time zone identifier while simultaneously demoting the renamed time zone identifier to non-primary. To provide ample time for other systems to be updated, the recommended rename waiting period is two years. However, it does not need to be either exact or dynamic. Instead, implementations should make the replacement time zone identifier primary after the waiting period as part of their normal release process for updating time zone data.

    A waiting period should only apply when a new Zone is added to replace an existing Zone. If an existing Zone and Link are swapped, then no renaming has happened and no waiting period is necessary.

    If implementations revise time zone information during the lifetime of an available named time zone identifier, and the UTC offsets and transitions associated with any agent. Due to the complexity of supporting this requirement, it is recommended that implementations maintain a fully consistent copy of the IANA Time Zone Database for the lifetime of each agent.

    This section complements but does not supersede 21.4.1.19.

    6.5.1 AvailableNamedTimeZoneIdentifiers ( )

    The Time Zone Identifier Records. Its result describes all available named time zone identifier. The Time Zone Identifier Record.

    This definition supersedes the definition provided in 21.4.1.23.

    1. Let identifiers be a List.
    2. For each element identifier of identifiers, do
      1. Let primary be identifier.
      2. If identifier is a Link name in the IANA Time Zone Database and identifier is not present in the “TZ” column of zone.tab of the IANA Time Zone Database, then
        1. Let zone be the Zone name that identifier resolves to, according to the rules for resolving Link names in the IANA Time Zone Database.
        2. If zone starts with "Etc/", then
          1. Set primary to zone.
        3. Else,
          1. Let identifierCountryCode be the substring of line from i + 5.
          2. Let backzoneAndLink be StringSplitToList(line, " ").
          3. Assert: backzone is not undefined.
          4. Set primary to backzone.
  • If primary is one of "Etc/UTC", "Etc/GMT", or "GMT", set primary to "UTC".
  • If primary is a replacement time zone identifier and its rename waiting period has not concluded, then
    1. Let renamedIdentifier be the renamed time zone identifier that primary replaced.
    2. Set primary to renamedIdentifier.
  • Let record be the Time Zone Identifier Record r such that r.[[Identifier]] is "UTC" and r.[[PrimaryIdentifier]] is "UTC".
  • Return result.
    •  Note 1

    The algorithm above for resolving Links to CLDR).

    This algorithm resolves Links to primary time zone identifiers without crossing the boundaries of ISO 3166-1 Alpha-2 country codes, using data from files zone.tab and backzone of the IANA Time Zone Database. If the country code of a Link has only one line in zone.tab, then that line will determine the primary time zone identifier. However, if that country code has multiple lines in zone.tab, then historical mappings in backzone must be used to identify the correct primary time zone identifier.

    For example, to resolve "Pacific/Truk" (in country code "FM") if the default build options of the IANA Time Zone Database identify it as a Link to "Pacific/Port_Moresby" (in country code "PG"), then the “country-code” column of zone.tab must be checked for lines corresponding with "FM". If there were only one such line, then the “TZ” column of that line would determine the primary time zone identifier associated with "Pacific/Truk". But if there are multiple "FM" lines in zone.tab, then backzone must be inspected and a line such as "Link Pacific/Chuuk Pacific/Truk" would result in using "Pacific/Chuuk" as the primary time zone identifier.

    Note that zone.tab is the preferred source of mapping data because backzone mappings may, in rare cases, cross the boundaries of ISO 3166-1 Alpha-2 country codes. For example, "Atlantic/Jan_Mayen" (in country code "SJ") is mapped in backzone to "Europe/Oslo" (in country code "NO"). As of the 2024a release of the IANA Time Zone Database, "Atlantic/Jan_Mayen" is the only case where this happens.

    Note 2
    Time zone identifiers in the IANA Time Zone Database can change over time. At a minimum, it is recommended that implementations limit changes to the result of AvailableNamedTimeZoneIdentifiers to the changes allowed by GetAvailableNamedTimeZoneIdentifier, for the lifetime of the surrounding agent. Due to the complexity of supporting these recommendations, it is recommended that the result of AvailableNamedTimeZoneIdentifiers remains the same for the lifetime of the surrounding agent.

    6.5.2 GetAvailableNamedTimeZoneIdentifier ( timeZoneIdentifier )

    The abstract operation GetAvailableNamedTimeZoneIdentifier takes argument timeZoneIdentifier (a String) and returns either a Time Zone Identifier Record or empty. If timeZoneIdentifier is an List returned by AvailableNamedTimeZoneIdentifiers. Otherwise, empty will be returned. It performs the following steps when called:

    1. For each element record of AvailableNamedTimeZoneIdentifiers(), do
      1. If record.[[Identifier]] is an ASCII-case-insensitive match for timeZoneIdentifier, return record.
    2. Return empty.
     Note
    For any timeZoneIdentifier, or any value that is an ASCII-case-insensitive match for it, it is required that the resulting surrounding agent. Furthermore, it is required that Time Zone Identifier Record where [[Identifier]] is [[PrimaryIdentifier]]. Due to the complexity of supporting these requirements, it is recommended that the result of AvailableNamedTimeZoneIdentifiers (and therefore GetAvailableNamedTimeZoneIdentifier too) remains the same for the lifetime of the surrounding agent.

    6.5.3 AvailablePrimaryTimeZoneIdentifiers ( )

    The abstract operation AvailablePrimaryTimeZoneIdentifiers takes no arguments and returns a List of supported Zone and Link names in the IANA Time Zone Database. It performs the following steps when called:

    1. Let records be AvailableNamedTimeZoneIdentifiers().
    2. Let result be a new empty List.
    3. For each element timeZoneIdentifierRecord of records, do
      1. If timeZoneIdentifierRecord.[[Identifier]] is timeZoneIdentifierRecord.[[PrimaryIdentifier]], then
        1. Append timeZoneIdentifierRecord.[[Identifier]] to result.
    4. Return result.

    6.5.4 StringSplitToList ( S, separator )

    The abstract operation StringSplitToList takes arguments S (a String) and separator (a String) and returns a List of Strings. The returned List contains all disjoint substrings of S that do not contain separator but are immediately preceded and/or immediately followed by an occurrence of separator. Each such substring will be the empty String between adjacent occurrences of separator, before a separator at the very start of S, or after a separator at the very end of S, but otherwise will not be empty. It performs the following steps when called:

    1. StringIndexOf(S, separator, 0).
    2. Repeat, while j is not not-found,
      1. Let T be the substring of S from i.
      2. Append T to substrings.
      3. Return substrings.

      6.6 Measurement Unit Identifiers

      This specification identifies measurement units using a core unit identifier (or equivalently core unit ID) as defined by Unicode Technical Standard #35 Part 2 General, Section 6.2 Unit Identifiers. Their canonical form is a string containing only Unicode Basic Latin lowercase letters (U+0061 LATIN SMALL LETTER A through U+007A LATIN SMALL LETTER Z) with zero or more medial hyphens (U+002D HYPHEN-MINUS).

      Only a limited set of core unit identifiers are sanctioned. Attempting to use an unsanctioned core unit identifier results in a RangeError.

      6.6.1 IsWellFormedUnitIdentifier ( unitIdentifier )

      The abstract operation IsWellFormedUnitIdentifier takes argument unitIdentifier (a String) and returns a Boolean. It verifies that the unitIdentifier argument represents a well-formed core unit identifier that is either a sanctioned single unit or a complex unit formed by division of two sanctioned single units. It performs the following steps when called:

      1. If IsSanctionedSingleUnitIdentifier(unitIdentifier) is true, then
        1. Return true.
      2. Let i be substring "-per-" occurs exactly once in unitIdentifier, at index i.
      3. Let numerator be the substring of unitIdentifier from i + 5.
      4. If IsSanctionedSingleUnitIdentifier(numerator) and IsSanctionedSingleUnitIdentifier(denominator) are both true, then
        1. Return true.
      5. Return false.

      6.6.2 IsSanctionedSingleUnitIdentifier ( unitIdentifier )

      The abstract operation IsSanctionedSingleUnitIdentifier takes argument unitIdentifier (a String) and returns a Boolean. It verifies that the unitIdentifier argument is among the single unit identifiers sanctioned in the current version of this specification, which are a subset of the Common Locale Data Repository Unicode Technical Standard #35 Part 2 General, Section 6.2 Unit Identifiers, a single unit identifier is a core unit identifier that is not composed of multiplication or division of other unit identifiers. It performs the following steps when called:

      1. If unitIdentifier is listed in Table 2 below, return true.
      2. Else, return false.
      Table 2: Single units sanctioned for use in ECMAScript
      Single Unit Identifier
      acre
      bit
      byte
      celsius
      centimeter
      day
      degree
      fahrenheit
      fluid-ounce
      foot
      gallon
      gigabit
      gigabyte
      gram
      hectare
      hour
      inch
      kilobit
      kilobyte
      kilogram
      kilometer
      liter
      megabit
      megabyte
      meter
      microsecond
      mile
      mile-scandinavian
      milliliter
      millimeter
      millisecond
      minute
      month
      nanosecond
      ounce
      percent
      petabyte
      pound
      second
      stone
      terabit
      terabyte
      week
      yard
      year

      6.6.3 AvailableCanonicalUnits ( )

      The abstract operation AvailableCanonicalUnits takes no arguments and returns a lexicographic code unit order, and consists of the unique values of simple unit identifiers listed in every row of Table 2, except the header row.

      6.7 Numbering System Identifiers

      This specification identifies numbering systems using a numbering system identifier corresponding with the name referenced by Unicode Technical Standard #35 Part 3 Numbers, Section 1 Numbering Systems. Their canonical form is a string containing only Unicode Basic Latin lowercase letters (U+0061 LATIN SMALL LETTER A through U+007A LATIN SMALL LETTER Z).

      6.7.1 AvailableCanonicalNumberingSystems ( )

      The lexicographic code unit order, and contains unique canonical numbering systems identifiers identifying the numbering systems for which the implementation provides the functionality of Intl.DateTimeFormat, Intl.NumberFormat, and Intl.RelativeTimeFormat objects. The List must include the Numbering System value of every row of Table 28, except the header row.

      6.8 Collation Types

      This specification identifies collations using a collation type as defined by Unicode Technical Standard #35 Part 5 Collation, Section 3.1 Collation Types. Their canonical form is a string containing only Unicode Basic Latin lowercase letters (U+0061 LATIN SMALL LETTER A through U+007A LATIN SMALL LETTER Z) with zero or more medial hyphens (U+002D HYPHEN-MINUS).

      6.8.1 AvailableCanonicalCollations ( )

      The lexicographic code unit order, and contains unique canonical collation types identifying the collations for which the implementation provides the functionality of Intl.Collator objects.

      6.9 Calendar Types

      This specification identifies calendars using a calendar type as defined by Unicode Technical Standard #35 Part 4 Dates, Section 2 Calendar Elements. Their canonical form is a string containing only Unicode Basic Latin lowercase letters (U+0061 LATIN SMALL LETTER A through U+007A LATIN SMALL LETTER Z) with zero or more medial hyphens (U+002D HYPHEN-MINUS).

      6.9.1 AvailableCalendars ( )

      The lexicographic code unit order, and contains unique calendar types in canonical form (6.9) identifying the calendars for which the implementation provides the functionality of Intl.DateTimeFormat objects, including their aliases (e.g., either both or neither of "islamicc" and "islamic-civil"). The List must include "iso8601".

      6.10 Pattern String Types

      Pattern String the ASCII word characters. The syntax of the abstract pattern strings is an implementation detail and is not exposed to users of ECMA-402.

      7 Requirements for Standard Built-in ECMAScript Objects

      Unless specified otherwise in this document, the objects, functions, and ECMAScript Standard Built-in Objects.

      8 The Intl Object

      The Intl object:

      • is %Intl%.
      • is the initial value of the "Intl" property of the global object.
      • is an ordinary object.
      • has a [[Prototype]] internal slot whose value is %Object.prototype%.
      • is not a function object.
      • does not have a [[Construct]] internal method; it cannot be used as a constructor with the new operator.
      • does not have a [[Call]] internal method; it cannot be invoked as a function.
      • has a [[FallbackSymbol]] internal slot, which is a new realm with the [[Description]] "IntlLegacyConstructedSymbol".

      8.1 Value Properties of the Intl Object

      8.1.1 Intl [ %Symbol.toStringTag% ]

      The initial value of the %Symbol.toStringTag% property is the String value "Intl".

      This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

      8.2 Constructor Properties of the Intl Object

      With the exception of Intl.Locale, each of the following constructors is a service constructor that creates objects providing locale-sensitive services.

      8.2.1 Intl.Collator ( . . . )

      See 10.

      8.2.2 Intl.DateTimeFormat ( . . . )

      See 11.

      8.2.3 Intl.DisplayNames ( . . . )

      See 12.

      8.2.4 Intl.DurationFormat ( . . . )

      See 13.

      8.2.5 Intl.ListFormat ( . . . )

      See 14.

      8.2.6 Intl.Locale ( . . . )

      See 15.

      8.2.7 Intl.NumberFormat ( . . . )

      See 16.

      8.2.8 Intl.PluralRules ( . . . )

      See 17.

      8.2.9 Intl.RelativeTimeFormat ( . . . )

      See 18.

      8.2.10 Intl.Segmenter ( . . . )

      See 19.

      8.3 Function Properties of the Intl Object

      8.3.1 Intl.getCanonicalLocales ( locales )

      When the getCanonicalLocales method is called with argument locales, the following steps are taken:

      1. Let ll be ? CanonicalizeLocaleList(locales).
      2. Return CreateArrayFromList(ll).

      8.3.2 Intl.supportedValuesOf ( key )

      When the supportedValuesOf method is called with argument key , the following steps are taken:

      1. Let key be ? CreateArrayFromList( list ).

      9 Locale and Parameter Negotiation

      Service constructors use common patterns to negotiate the requests represented by locales and options arguments against the actual capabilities of an implementation. That common behaviour is explained here in terms of internal slots describing the capabilities, abstract operations using these internal slots, and specialized data types defined below.

      An Available Locales List is an arbitrarily-ordered duplicate-free List of language tags, each of which is structurally valid, canonicalized, and lacks a Unicode locale extension sequence. It represents all locales for which the implementation provides functionality within a particular context.

      A Language Priority List is a RFC 4647 section 2.3 but prohibits "*" elements and contains only canonicalized contents.

      A Resolution Option Descriptor is a ECMAScript language values). It describes how to read options relevant to locale resolution during object construction.

      9.1 Internal slots of Service Constructors

      Each service constructor has the following internal slots:

      • [[AvailableLocales]] is an Available Locales List. It must include the value returned by DefaultLocale. Additionally, for each element with more than one subtag, it must also include a less narrow language tag with the same language subtag and a strict subset of the same following subtags (i.e., omitting one or more) to serve as a potential fallback from ResolveLocale. In particular, each element with a language subtag and a script subtag and a region subtag must be accompanied by another element consisting of only the same language subtag and region subtag but missing the script subtag. For example,
        • If [[AvailableLocales]] contains "de-DE", then it must also contain "de" (which might be selected to satisfy requested locales such as "de-AT" and "de-CH").
        • If [[AvailableLocales]] contains "az-Latn-AZ", then it must also contain "az-AZ" (which might be selected to satisfy requested locales such as "az-Cyrl-AZ" if "az-Cyrl" is unavailable).
      • [[RelevantExtensionKeys]] is a Unicode Technical Standard #35 Part 1 Core, Section 3.6.1 Key and Type Definitions that are relevant for the functionality of the constructed objects.
      • [[ResolutionOptionDescriptors]] is a List of Resolution Option Descriptors used for reading options during object construction.
      • [[SortLocaleData]] and [[SearchLocaleData]] (for Intl.Collator) and [[LocaleData]] (for every other service constructor) are List of Strings representing the type values that are supported by the implementation in the relevant locale for the corresponding Unicode locale extension sequence key, with the first element providing the default value for that key in the locale.
      Note
      For example, an implementation of DateTimeFormat might include the language tag "fa-IR" in its [[AvailableLocales]] internal slot, and must (according to 11.2.3) include the keys "ca", "hc", and "nu" in its [[RelevantExtensionKeys]] internal slot. The default calendar for that locale is usually "persian", but an implementation might also support "gregory", "islamic", and "islamic-civil". The Lists.

      9.2 Abstract Operations

      9.2.1 CanonicalizeLocaleList ( locales )

      The abstract operation CanonicalizeLocaleList takes argument locales (an throw completion. It performs the following steps when called:

      1. If locales is undefined, then
        1. Return a new empty is an Object and locales has an [[InitializedLocale]] internal slot, then
          1. Let O be ToString(is not a String and kValue ToString(kValue).
        2. If IsStructurallyValidLanguageTag(tag) is false, throw a RangeError exception.
        3. Let canonicalizedTag be CanonicalizeUnicodeLocaleId(tag).
        4. If seen does not contain canonicalizedTag, append canonicalizedTag to seen.
      2. Set k to k + 1.
    3. Return seen.
     Note 1
    Non-normative summary: The abstract operation interprets the locales argument as an array and copies its elements into a List, validating the elements as structurally valid language tags and canonicalizing them, and omitting duplicates.
    Note 2
    Requiring kValue to be a String or Object means that the Number value NaN will not be interpreted as the language tag "nan", which stands for Min Nan Chinese.

    9.2.2 CanonicalizeUValue ( ukey, uvalue )

    The abstract operation CanonicalizeUValue takes arguments ukey (a Unicode locale extension sequence key defined in Unicode Technical Standard #35 Part 1 Core Section 3.6.1 Key and Type Definitions) and uvalue (a String) and returns a String. The returned String is the canonical and case-regularized form of uvalue as a value of ukey. It performs the following steps when called:

    1. Let lowerValue be the ASCII-lowercase of uvalue.
    2. Let canonicalized be the String value resulting from canonicalizing lowerValue as a value of key ukey per Unicode Technical Standard #35 Part 1 Core, Annex C LocaleId Canonicalization Section 5 Canonicalizing Syntax, Processing LocaleIds.
    3. NOTE: It is recommended that implementations use the 'u' extension data in common/bcp47 provided by the Common Locale Data Repository (available at https://cldr.unicode.org/).
    4. Return canonicalized.

    9.2.3 LookupMatchingLocaleByPrefix ( availableLocales, requestedLocales )

    The abstract operation LookupMatchingLocaleByPrefix takes arguments availableLocales (an Available Locales List) and requestedLocales (a Language Priority List) and returns a Record with a [[locale]] field containing the matching language tag from availableLocales and an [[extension]] field containing the Unicode locale extension sequence of the corresponding element of requestedLocales (or empty if requested language tag has no such sequence). It performs the following steps when called:

    1. For each element locale of requestedLocales, do
      1. Let extension be empty.
      2. If locale contains a Unicode locale extension sequence, then
        1. Set extension to the Unicode locale extension sequence of locale.
        2. Set locale to the String value that is locale with any Unicode locale extension sequences removed.
      3. Let prefix be locale.
      4. Repeat, while prefix is not the empty String,
        1. If availableLocales contains prefix, return the substring of prefix from 0 to pos.
    2. Return undefined.
     Note
    When a requested locale includes a Unicode Technical Standard #35 Part 1 Core BCP 47 T Extension subtag sequence, the truncation in this algorithm may temporarily generate invalid language tags. However, none of them will be returned because availableLocales contains only valid language tags.

    9.2.4 LookupMatchingLocaleByBestFit ( availableLocales, requestedLocales )

    The Record with a [[locale]] field containing the matching language tag from availableLocales and an [[extension]] field containing the Unicode locale extension sequence of the corresponding element of requestedLocales (or empty if requested language tag has no such sequence).

    9.2.5 UnicodeExtensionComponents ( extension )

    The abstract operation UnicodeExtensionComponents takes argument extension (a Unicode locale extension sequence) and returns a List of keywords with unique keys. Any repeated appearance of an attribute or keyword key after the first is ignored. It performs the following steps when called:

    1. List.
    2. Let keywords be a new empty inclusive interval from 3 to 8, collectively constituting a value along with their medial "-" separators. An attribute is a single subtag with length in the string-concatenation of keyword.[[Value]], "-", and subtag.
  • Set k to k + len + 1.
  • Return the Record { [[Attributes]]: attributes, [[Keywords]]: keywords }.
    •

    9.2.6 InsertUnicodeExtensionAndCanonicalize ( locale, attributes, keywords )

    The abstract operation InsertUnicodeExtensionAndCanonicalize takes arguments locale (a language tag), attributes (a Records) and returns a Unicode canonicalized locale identifier. It incorporates attributes and keywords into locale as a Unicode locale extension sequence and returns the canonicalized result. It performs the following steps when called:

    1. string-concatenation of extension, "-", and keyword.[[Key]].
    2. If keyword.[[Value]] is not the empty String, set extension to the substring of locale from 0 to privateIndex.
    3. Let postExtension be the Assert: IsStructurallyValidLanguageTag(newLocale) is true.
    4. Return CanonicalizeUnicodeLocaleId(newLocale).

    9.2.7 ResolveLocale ( availableLocales, requestedLocales, options, relevantExtensionKeys, localeData )

    The abstract operation ResolveLocale takes arguments availableLocales (an Available Locales List), requestedLocales (a Language Priority List), options (a Record. It performs "lookup" as defined in Record, omitting any keyword Unicode locale nonterminal whose key value is not contained within relevantExtensionKeys or type value is superseded by a different value from options. It performs the following steps when called:

    1. Let matcher be options.[[localeMatcher]].
    2. If matcher is "lookup", then
      1. Let r be LookupMatchingLocaleByPrefix(availableLocales, requestedLocales).
    3. Else,
      1. Let r be LookupMatchingLocaleByBestFit(availableLocales, requestedLocales).
    4. If r is undefined, set r to the Record.
    5. Set result.[[LocaleData]] to foundLocaleData.
    6. If r.[[extension]] is not empty, then
      1. Let components be UnicodeExtensionComponents(r.[[extension]]).
      2. Let keywords be components.[[Keywords]].
    7. Else,
      1. Let keywords be a new empty List.
      2. Let value be keyLocaleData[0].
      3. Record { [[Key]]: key, [[Value]]: "" }.
  • is a String, then
    1. Let ukey be the ASCII-lowercase of key.
    2. Set optionsValue to CanonicalizeUValue(ukey, optionsValue).
    3. If optionsValue is the empty String, then
      1. Set optionsValue to "true".
  • If List.
  • Set foundLocale to InsertUnicodeExtensionAndCanonicalize(foundLocale, supportedAttributes, supportedKeywords).
  • Set result.[[Locale]] to foundLocale.
  • Return result.
    •

    9.2.8 ResolveOptions ( constructor, localeData, locales, options [ , specialBehaviours [ , modifyResolutionOptions ] ] )

    The abstract operation ResolveOptions takes arguments constructor (a service constructor), localeData (a List of Record with fields [[Options]] (an Object), [[ResolvedLocale]] (a throw completion. It reads the inputs for constructor and resolves them into a locale. It performs the following steps when called:

    1. Let requestedLocales be ? CanonicalizeLocaleList(locales).
    2. If specialBehaviours is present and contains require-options and options is undefined, throw a TypeError exception.
    3. If specialBehaviours is present and contains coerce-options, set options to ? CoerceOptionsToObject(options). Otherwise, set options to ? GetOptionsObject(options).
    4. Let matcher be ? GetOption(options, "localeMatcher", string, « "lookup", "best fit" », "best fit").
    5. Let opt be the Record { [[Options]]: options, [[ResolvedLocale]]: resolution, [[ResolutionOptions]]: opt }.

    9.2.9 FilterLocales ( availableLocales, requestedLocales, options )

    The abstract operation FilterLocales takes arguments availableLocales (an Available Locales List), requestedLocales (a Language Priority List), and options (an throw completion. It performs "filtering" as defined in RFC 4647 section 3, returning the elements of requestedLocales for which availableLocales contains a matching locale when using either the LookupMatchingLocaleByBestFit algorithm or LookupMatchingLocaleByPrefix algorithm as specified in options, preserving their relative order. It performs the following steps when called:

    1. Set options to ? CoerceOptionsToObject(options).
    2. Let matcher be ? GetOption(options, "localeMatcher", string, « "lookup", "best fit" », "best fit").
    3. Let subset be a new empty CreateArrayFromList(subset).

    9.2.10 GetOptionsObject ( options )

    The abstract operation GetOptionsObject takes argument options (an throw completion. It returns an Object suitable for use with GetOption, either options itself or a default empty Object. It throws a TypeError if options is not undefined and not an Object. It performs the following steps when called:

    1. If options is undefined, then
      1. Return is an Object, then
        1. Return options.
      2. Throw a TypeError exception.

      9.2.11 CoerceOptionsToObject ( options )

      The abstract operation CoerceOptionsToObject takes argument options (an throw completion. It coerces options into an Object suitable for use with GetOption, defaulting to an empty Object. Because it coerces non-null primitive values into objects, its use is discouraged for new functionality in favour of GetOptionsObject. It performs the following steps when called:

      1. If options is undefined, then
        1. Return ToObject(options).

        9.2.12 GetOption ( options, property, type, values, default )

        The abstract operation GetOption takes arguments options (an Object), property (a ECMAScript language value) and returns either a throw completion. It extracts the value of the specified property of options, converts it to the required type, checks whether it is allowed by values if values is not empty, and substitutes default if the value is undefined. It performs the following steps when called:

        1. Let value be ? ToString(value).
      2. If values is not empty and values does not contain value, throw a RangeError exception.
      3. Return value.

      9.2.13 GetBooleanOrStringNumberFormatOption ( options, property, stringValues, fallback )

      The abstract operation GetBooleanOrStringNumberFormatOption takes arguments options (an Object), property (a normal completion containing either a Boolean, String, or fallback, or a throw completion. It extracts the value of the property named property from the provided options object. It returns fallback if that value is undefined, true if that value is true, false if that value coerces to false, and otherwise coerces it to a String and returns the result if it is allowed by stringValues. It performs the following steps when called:

      1. Let value be ? ToString(value).
      2. If stringValues does not contain value, throw a RangeError exception.
      3. Return value.

      9.2.14 DefaultNumberOption ( value, minimum, maximum, fallback )

      The abstract operation DefaultNumberOption takes arguments value (an integer or undefined) and returns either a integer, checks whether it is in the allowed range, and fills in a fallback value if necessary. It performs the following steps when called:

      1. If value is undefined, return fallback.
      2. Set value to ? ℝ(value) > maximum, throw a RangeError exception.
      3. Return ℝ(value)).

      9.2.15 GetNumberOption ( options, property, minimum, maximum, fallback )

      The abstract operation GetNumberOption takes arguments options (an Object), property (a String), minimum (an normal completion containing either an integer, checks whether it is in the allowed range, and fills in a fallback value if necessary. It performs the following steps when called:

      1. Let value be ? Get(options, property).
      2. Return ? DefaultNumberOption(value, minimum, maximum, fallback).

      9.2.16 PartitionPattern ( pattern )

      The abstract operation PartitionPattern takes argument pattern (a Pattern String) and returns a Records with fields [[Type]] (a String) and [[Value]] (a String or undefined). The [[Value]] field will be a String value if [[Type]] is "literal", and undefined otherwise. It performs the following steps when called:

      1. Let result be a new empty Record { [[Type]]: "literal", [[Value]]: literal } to result.
    2. Set placeholderEnd to Record { [[Type]]: placeholderName, [[Value]]: undefined } to result.
    3. Set placeholderStart to Record { [[Type]]: "literal", [[Value]]: tail } to result.
  • Return result.
    •

    10 Collator Objects

    10.1 The Intl.Collator Constructor

    The Intl.Collator constructor:

    • is %Intl.Collator%.
    • is the initial value of the "Collator" property of the Intl object.

    Behaviour common to all service constructor properties of the Intl object is specified in 9.1.

    10.1.1 Intl.Collator ( [ locales [ , options ] ] )

    When the Intl.Collator function is called with optional arguments locales and options, the following steps are taken:

    1. If NewTarget is undefined, let newTarget be the SameValue(r.[[kn]], "true").
    2. Set collator.[[CaseFirst]] to r.[[kf]].
    3. Let resolvedLocaleData be r.[[LocaleData]].
    4. If usage is "sort", let defaultSensitivity be "variant". Otherwise, let defaultSensitivity be resolvedLocaleData.[[sensitivity]].
    5. Set collator.[[Sensitivity]] to ? GetOption(options, "sensitivity", string, « "base", "accent", "case", "variant" », defaultSensitivity).
    6. Let defaultIgnorePunctuation be resolvedLocaleData.[[ignorePunctuation]].
    7. Set collator.[[IgnorePunctuation]] to ? GetOption(options, "ignorePunctuation", boolean, empty, defaultIgnorePunctuation).
    8. Return collator.
         Note
    The collation associated with the "search" value for the "usage" option should only be used to find matching strings, since this collation is not guaranteed to be in any particular order. This behaviour is described in Unicode Technical Standard #10 Unicode Collation Algorithm, Searching and Matching.

    10.2 Properties of the Intl.Collator Constructor

    The Intl.Collator constructor:

    • has a [[Prototype]] internal slot whose value is %Function.prototype%.
    • has the following properties:

    10.2.1 Intl.Collator.prototype

    The value of Intl.Collator.prototype is %Intl.Collator.prototype%.

    This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.

    10.2.2 Intl.Collator.supportedLocalesOf ( locales [ , options ] )

    When the supportedLocalesOf method is called with arguments locales and options, the following steps are taken:

    1. Let availableLocales be %Intl.Collator%.[[AvailableLocales]].
    2. Let requestedLocales be ? CanonicalizeLocaleList(locales).
    3. Return ? FilterLocales(availableLocales, requestedLocales, options).

    10.2.3 Internal slots

    The value of the [[AvailableLocales]] internal slot is List that must include the element "co", may include any or all of the elements "kf" and "kn", and must not include any other elements.

    Note
    Unicode Technical Standard #35 Part 1 Core, Section 3.6.1 Key and Type Definitions describes ten locale extension keys that are relevant to collation: "co" for collator usage and specializations, "ka" for alternate handling, "kb" for backward second level weight, "kc" for case level, "kf" for case first, "kh" for hiragana quaternary, "kk" for normalization, "kn" for numeric, "kr" for reordering, "ks" for collation strength, and "vt" for variable top. Collator, however, requires that the usage is specified through the "usage" property of the options object, alternate handling through the "ignorePunctuation" property of the options object, and case level and the strength through the "sensitivity" property of the options object. The "co" key in the language tag is supported only for collator specializations, and the keys "kb", "kh", "kk", "kr", and "vt" are not allowed in this version of the Internationalization API. Support for the remaining keys is implementation dependent.

    The value of the [[ResolutionOptionDescriptors]] internal slot is « { [[Key]]: "co", [[Property]]: "collation" }, { [[Key]]: "kn", [[Property]]: "numeric", [[Type]]: boolean }, { [[Key]]: "kf", [[Property]]: "caseFirst", [[Values]]: « "upper", "lower", "false" » } ».

    The values of the [[SortLocaleData]] and [[SearchLocaleData]] internal slots are implementation-defined within the constraints described in 9.1 and the following additional constraints, for all locale values locale:

    • The first element of [[SortLocaleData]].[[<locale>]].[[co]] and [[SearchLocaleData]].[[<locale>]].[[co]] must be null.
    • The values "standard" and "search" must not be used as elements in any [[SortLocaleData]].[[<locale>]].[[co]] and [[SearchLocaleData]].[[<locale>]].[[co]] List.
    • [[SearchLocaleData]].[[<locale>]] must have a [[sensitivity]] field with one of the String values "base", "accent", "case", or "variant".
    • [[SearchLocaleData]].[[<locale>]] and [[SortLocaleData]].[[<locale>]] must have an [[ignorePunctuation]] field with a Boolean value.

    10.3 Properties of the Intl.Collator Prototype Object

    The Intl.Collator prototype object:

    • is %Intl.Collator.prototype%.
    • is an ordinary object.
    • is not an Intl.Collator instance and does not have an [[InitializedCollator]] internal slot or any of the other internal slots of Intl.Collator instance objects.
    • has a [[Prototype]] internal slot whose value is %Object.prototype%.

    10.3.1 Intl.Collator.prototype.constructor

    The initial value of Intl.Collator.prototype.constructor is %Intl.Collator%.

    10.3.2 Intl.Collator.prototype.resolvedOptions ( )

    This function provides access to the locale and options computed during initialization of the object.

    1. Let collator be the this value.
    2. Perform ? CreateDataPropertyOrThrow(options, p, v).
  • Return options.
    •
    Table 3: Resolved Options of Collator Instances
    Internal Slot Property Extension Key
    [[Locale]] "locale"
    [[Usage]] "usage"
    [[Sensitivity]] "sensitivity"
    [[IgnorePunctuation]] "ignorePunctuation"
    [[Collation]] "collation"
    [[Numeric]] "numeric" "kn"
    [[CaseFirst]] "caseFirst" "kf"

    10.3.3 get Intl.Collator.prototype.compare

    This named sort order of this Collator object.

    Intl.Collator.prototype.compare is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

    1. Let collator be the this value.
    2. Perform ? function object as defined in 10.3.3.1.
    3. Set F.[[Collator]] to collator.
    4. Set collator.[[BoundCompare]] to F.
  • Return collator.[[BoundCompare]].
    •  Note
    The returned function is bound to collator so that it can be passed directly to Array.prototype.sort or other functions.

    10.3.3.1 Collator Compare Functions

    A Collator compare function is an anonymous built-in function that has a [[Collator]] internal slot.

    When a Collator compare function F is called with arguments x and y, the following steps are taken:

    1. Let collator be F.[[Collator]].
    2. ToString(y).
    3. Return CompareStrings(collator, X, Y).

    The "length" property of a Collator compare function is 2𝔽.

    10.3.3.2 CompareStrings ( collator, x, y )

    The implementation-defined abstract operation CompareStrings takes arguments collator (an Intl.Collator), x (a String), and y (a String) and returns a Number, but not NaN. The returned Number represents the result of an implementation-defined locale-sensitive String comparison of x with y. The result is intended to correspond with a sort order of String values according to the effective locale and collation options of collator, and will be negative when x is ordered before y, positive when x is ordered after y, and zero in all other cases (representing no relative ordering between x and y). String values must be interpreted as UTF-16 code unit sequences as described in ECMA-262, surrogate pair (a code unit in the range 0xD800 to 0xDBFF followed by a code unit in the range 0xDC00 to 0xDFFF) within a string must be interpreted as the corresponding code point.

    Behaviour as described below depends upon locale-sensitive identification of the sequence of collation elements for a string, in particular "base letters", and different base letters always compare as unequal (causing the strings containing them to also compare as unequal). Results of comparing variations of the same base letter with different case, diacritic marks, or potentially other aspects further depends upon collator.[[Sensitivity]] as follows:

    Table 4: Effects of Collator Sensitivity
    [[Sensitivity]] Description "a" vs. "á" "a" vs. "A"
    "base" Characters with the same base letter do not compare as unequal, regardless of differences in case and/or diacritic marks. equal
    "accent" Characters with the same base letter compare as unequal only if they differ in accents and/or other diacritic marks, regardless of differences in case. not equal equal
    "case" Characters with the same base letter compare as unequal only if they differ in case, regardless of differences in accents and/or other diacritic marks. equal not equal
    "variant" Characters with the same base letter compare as unequal if they differ in case, diacritic marks, and/or potentially other differences. not equal
    Note 1
    The mapping from input code points to base letters can include arbitrary contractions, expansions, and collisions, including those that apply special treatment to certain characters with diacritic marks. For example, in Swedish, "ö" is a base letter that differs from "o", and "v" and "w" are considered to be the same base letter. In Slovak, "ch" is a single base letter, and in English, "æ" is a sequence of base letters starting with "a" and ending with "e".

    If collator.[[IgnorePunctuation]] is true, then punctuation is ignored (e.g., strings that differ only in punctuation compare as equal).

    For the interpretation of options settable through locale extension keys, see Unicode Technical Standard #35 Part 1 Core, Section 3.6.1 Key and Type Definitions.

    The actual return values are consistent comparator defining a total ordering on the set of all Strings. This operation is also required to recognize and honour canonical equivalence according to the Unicode Standard, including returning +0𝔽 when comparing distinguishable Strings that are canonically equivalent.

    Note 2
    It is recommended that the CompareStrings abstract operation be implemented following Unicode Technical Standard #10: Unicode Collation Algorithm, using tailorings for the effective locale and collation options of collator. It is recommended that implementations use the tailorings provided by the Common Locale Data Repository (available at https://cldr.unicode.org/).
    Note 3
    Applications should not assume that the behaviour of the CompareStrings abstract operation for Collator instances with the same resolved options will remain the same for different versions of the same implementation.

    10.3.4 Intl.Collator.prototype [ %Symbol.toStringTag% ]

    The initial value of the %Symbol.toStringTag% property is the String value "Intl.Collator".

    This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

    10.4 Properties of Intl.Collator Instances

    Intl.Collator instances are ordinary objects that inherit properties from %Intl.Collator.prototype%.

    Intl.Collator instances have an [[InitializedCollator]] internal slot.

    Intl.Collator instances also have several internal slots that are computed by The Intl.Collator Constructor:

    • [[Locale]] is a String value with the language tag of the locale whose localization is used for collation.
    • [[Usage]] is one of the String values "sort" or "search", identifying the collator usage.
    • [[Sensitivity]] is one of the String values "base", "accent", "case", or "variant", identifying the collator's sensitivity.
    • [[IgnorePunctuation]] is a Boolean value, specifying whether punctuation should be ignored in comparisons.
    • [[Collation]] Unicode Collation Identifier used for collation, except that the values "standard" and "search" are not allowed, while the value "default" is allowed.

    Intl.Collator instances also have the following internal slots if the key corresponding to the name of the internal slot in Table 3 is included in the [[RelevantExtensionKeys]] internal slot of Intl.Collator:

    • [[Numeric]] is a Boolean value, specifying whether numeric sorting is used.
    • [[CaseFirst]] is one of the String values "upper", "lower", or "false".

    Finally, Intl.Collator instances have a [[BoundCompare]] internal slot that caches the function returned by the compare accessor (10.3.3).

    11 DateTimeFormat Objects

    11.1 The Intl.DateTimeFormat Constructor

    The Intl.DateTimeFormat constructor:

    • is %Intl.DateTimeFormat%.
    • is the initial value of the "DateTimeFormat" property of the Intl object.

    Behaviour common to all service constructor properties of the Intl object is specified in 9.1.

    11.1.1 Intl.DateTimeFormat ( [ locales [ , options ] ] )

    When the Intl.DateTimeFormat function is called with optional arguments locales and options, the following steps are taken:

    1. If NewTarget is undefined, let newTarget be the constructor mode of 4.3 Note 1, then
      1. Let this be the this value.
      2. Return ? ChainDateTimeFormat(dateTimeFormat, NewTarget, this).
    2. Return dateTimeFormat.
    Normative Optional

    11.1.1.1 ChainDateTimeFormat ( dateTimeFormat, newTarget, this )

    The abstract operation ChainDateTimeFormat takes arguments dateTimeFormat (an Intl.DateTimeFormat), newTarget (an throw completion. It performs the following steps when called:

    1. If newTarget is undefined and ? DefinePropertyOrThrow(this, %Intl%.[[FallbackSymbol]], PropertyDescriptor{ [[Value]]: dateTimeFormat, [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }).
    2. Return this.
  • Return dateTimeFormat.
    •

    11.1.2 CreateDateTimeFormat ( newTarget, locales, options, required, defaults )

    The abstract operation CreateDateTimeFormat takes arguments newTarget (a normal completion containing a DateTimeFormat object or a throw completion. It performs the following steps when called:

    1. Let dateTimeFormat be ? Get(options, "timeZone").
    2. If timeZone is undefined, then
      1. Set timeZone to ParseText(Parse Node.
      2. If parseResult contains more than one Assert: offsetMinutes is an property name prop of « "weekday", "year", "month", "day" », do
        1. Let value be formatOptions.[[<prop>]].
        2. If value is not undefined, set needDefaults to false.
    3. If required is time or any, then
      1. For each property name prop of « "hour", "minute", "second" », do
        1. Set formatOptions.[[<prop>]] to "numeric".
    4. Let formats be resolvedLocaleData.[[formats]].[[<resolvedCalendar>]].
    5. If formatMatcher is "basic", then
      1. Let bestFormat be BasicFormatMatcher(formatOptions, formats).
    6. Else,
      1. Let bestFormat be BestFitFormatMatcher(formatOptions, formats).
  • Set dateTimeFormat.[[DateTimeFormat]] to bestFormat.
  • If bestFormat has a field [[hour]], then
    1. Set dateTimeFormat.[[HourCycle]] to hc.
  • Return dateTimeFormat.
    •

    11.1.3 FormatOffsetTimeZoneIdentifier ( offsetMinutes )

    The abstract operation FormatOffsetTimeZoneIdentifier takes argument offsetMinutes (an integer) and returns a String. It formats a UTC offset, in minutes, into a UTC offset string formatted like ±HH:MM. It performs the following steps when called:

    1. If offsetMinutes ≥ 0, let sign be the code unit 0x002B (PLUS SIGN); otherwise, let sign be the code unit 0x002D (HYPHEN-MINUS).
    2. Let absoluteMinutes be string-concatenation of sign, ToZeroPaddedDecimalString(minutes, 2).

    11.2 Properties of the Intl.DateTimeFormat Constructor

    The Intl.DateTimeFormat constructor:

    • has a [[Prototype]] internal slot whose value is %Function.prototype%.
    • has the following properties:

    11.2.1 Intl.DateTimeFormat.prototype

    The value of Intl.DateTimeFormat.prototype is %Intl.DateTimeFormat.prototype%.

    This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.

    11.2.2 Intl.DateTimeFormat.supportedLocalesOf ( locales [ , options ] )

    When the supportedLocalesOf method is called with arguments locales and options, the following steps are taken:

    1. Let availableLocales be %Intl.DateTimeFormat%.[[AvailableLocales]].
    2. Let requestedLocales be ? CanonicalizeLocaleList(locales).
    3. Return ? FilterLocales(availableLocales, requestedLocales, options).

    11.2.3 Internal slots

    The value of the [[AvailableLocales]] internal slot is implementation-defined within the constraints described in 9.1.

    The value of the [[RelevantExtensionKeys]] internal slot is « "ca", "hc", "nu" ».

    Note 1
    Unicode Technical Standard #35 Part 1 Core, Section 3.6.1 Key and Type Definitions describes four locale extension keys that are relevant to date and time formatting: "ca" for calendar, "hc" for hour cycle, "nu" for numbering system (of formatted numbers), and "tz" for time zone. DateTimeFormat, however, requires that the time zone is specified through the "timeZone" property in the options objects.

    The value of the [[ResolutionOptionDescriptors]] internal slot is « { [[Key]]: "ca", [[Property]]: "calendar" }, { [[Key]]: "nu", [[Property]]: "numberingSystem" }, { [[Key]]: "hour12", [[Property]]: "hour12", [[Type]]: boolean }, { [[Key]]: "hc", [[Property]]: "hourCycle", [[Values]]: « "h11", "h12", "h23", "h24" » } ».

    The value of the [[LocaleData]] internal slot is implementation-defined within the constraints described in 9.1 and the following additional constraints, for all locale values locale:

    • [[LocaleData]].[[<locale>]].[[nu]] must be a List that does not include the values "native", "traditio", or "finance".
    • [[LocaleData]].[[<locale>]].[[hc]] must be « null, "h11", "h12", "h23", "h24" ».
    • [[LocaleData]].[[<locale>]].[[hourCycle]] must be one of the String values "h11", "h12", "h23", or "h24".
    • [[LocaleData]].[[<locale>]].[[hourCycle12]] must be one of the String values "h11" or "h12".
    • [[LocaleData]].[[<locale>]].[[hourCycle24]] must be one of the String values "h23" or "h24".
    • [[LocaleData]].[[<locale>]] must have a [[formats]] field. The value of this [[formats]] field must be a List may use the same subset of the fields as long as the corresponding values differ for at least one field. The following subsets must be available for each locale:
      • weekday, year, month, day, hour, minute, second, fractionalSecondDigits
      • weekday, year, month, day, hour, minute, second
      • weekday, year, month, day
      • year, month, day
      • year, month
      • month, day
      • month
      • hour, minute, second, fractionalSecondDigits
      • hour, minute, second
      • hour, minute
      • dayPeriod, hour, minute, second, fractionalSecondDigits
      • dayPeriod, hour, minute, second
      • dayPeriod, hour, minute
      • dayPeriod, hour
    • [[LocaleData]].[[<locale>]] must have a [[styles]] field. The value of this [[styles]] field must be a Record with a [[<calendar>]] field for each calendar value calendar. The value of each [[<calendar>]] field must be a DateTime Styles Record.

    11.2.3.1 DateTime Format Records

    Each DateTime Format Record has the fields defined in Table 5.

    Table 5: DateTime Format Record
    Field Name Value Type Description
    [[weekday]] [[Weekday]] values in the Values column of Table 16 Optional field. Present if [[pattern]] contains the substring "{weekday}".
    [[era]] [[Era]] values in the Values column of Table 16 Optional field. Present if [[pattern]] contains the substring "{era}".
    [[year]] [[Year]] values in the Values column of Table 16 Optional field. Present if [[pattern]] contains at least one of the substrings "{year}", "{yearName}", or "{relatedYear}".
    [[month]] [[Month]] values in the Values column of Table 16 Optional field. Present if [[pattern]] contains the substring "{month}".
    [[day]] [[Day]] values in the Values column of Table 16 Optional field. Present if [[pattern]] contains the substring "{day}".
    [[dayPeriod]] [[DayPeriod]] values in the Values column of Table 16 Optional field. Present if [[pattern]] contains the substring "{dayPeriod}".
    [[hour]] [[Hour]] values in the Values column of Table 16 Optional field. Present if [[pattern]] contains the substring "{hour}".
    [[minute]] [[Minute]] values in the Values column of Table 16 Optional field. Present if [[pattern]] contains the substring "{minute}".
    [[second]] [[Second]] values in the Values column of Table 16 Optional field. Present if [[pattern]] contains the substring "{second}".
    [[fractionalSecondDigits]] [[FractionalSecondDigits]] values in the Values column of Table 16 Optional field. Present if [[pattern]] contains the substring "{fractionalSecondDigits}".
    [[timeZoneName]] [[TimeZoneName]] values in the Values column of Table 16 Optional field. Present if [[pattern]] contains the substring "{timeZoneName}".
    [[pattern]] a Pattern String Contains for each of the date and time format component fields of the record a substring starting with "{", followed by the name of the field, followed by "}". If the record has a [[year]] field, the string may contain the substrings "{yearName}" and "{relatedYear}".
    [[pattern12]] a Pattern String Optional field. Present if the [[hour]] field is present. In addition to the substrings of the [[pattern]] field, contains at least one of the substrings "{ampm}" or "{dayPeriod}".
    [[rangePatterns]] a DateTime Range Pattern Record Pattern strings in this field are similar to [[pattern]].
    [[rangePatterns12]] a DateTime Range Pattern Record Optional field. Present if the [[hour]] field is present. Pattern strings in this field are similar to [[pattern12]].

    11.2.3.2 DateTime Range Pattern Records

    Each DateTime Range Pattern Record has the fields defined in Table 6.

    Table 6: DateTime Range Pattern Record
    Field Name Value Type Description
    [[Default]] a DateTime Range Pattern Format Record It contains the default range pattern used when a more specific range pattern is not available.
    [[Era]] a DateTime Range Pattern Format Record Optional field. Used when era is the largest calendar element that is different between the start and end dates.
    [[Year]] a DateTime Range Pattern Format Record Optional field. Used when year is the largest calendar element that is different between the start and end dates.
    [[Month]] a DateTime Range Pattern Format Record Optional field. Used when month is the largest calendar element that is different between the start and end dates.
    [[Day]] a DateTime Range Pattern Format Record Optional field. Used when day is the largest calendar element that is different between the start and end dates.
    [[AmPm]] a DateTime Range Pattern Format Record Optional field. Used when ante or post meridiem is the largest calendar element that is different between the start and end dates.
    [[DayPeriod]] a DateTime Range Pattern Format Record Optional field. Used when day period is the largest calendar element that is different between the start and end dates.
    [[Hour]] a DateTime Range Pattern Format Record Optional field. Used when hour is the largest calendar element that is different between the start and end dates.
    [[Minute]] a DateTime Range Pattern Format Record Optional field. Used when minute is the largest calendar element that is different between the start and end dates.
    [[Second]] a DateTime Range Pattern Format Record Optional field. Used when second is the largest calendar element that is different between the start and end dates.
    [[FractionalSecondDigits]] a DateTime Range Pattern Format Record Optional field. Used when fractional seconds are the largest calendar element that is different between the start and end dates.

    11.2.3.3 DateTime Range Pattern Format Records

    Each DateTime Range Pattern Format Record has the fields defined in Table 7.

    Table 7: DateTime Range Pattern Format Record
    Field Name Value Type Description
    [[weekday]] [[Weekday]] values in the Values column of Table 16 Optional field. Present if a Pattern String in [[PatternParts]] contains the substring "{weekday}".
    [[era]] [[Era]] values in the Values column of Table 16 Optional field. Present if a Pattern String in [[PatternParts]] contains the substring "{era}".
    [[year]] [[Year]] values in the Values column of Table 16 Optional field. Present if a Pattern String in [[PatternParts]] contains at least one of the substrings "{year}", "{yearName}", or "{relatedYear}".
    [[month]] [[Month]] values in the Values column of Table 16 Optional field. Present if a Pattern String in [[PatternParts]] contains the substring "{month}".
    [[day]] [[Day]] values in the Values column of Table 16 Optional field. Present if a Pattern String in [[PatternParts]] contains the substring "{day}".
    [[dayPeriod]] [[DayPeriod]] values in the Values column of Table 16 Optional field. Present if a Pattern String in [[PatternParts]] contains the substring "{dayPeriod}".
    [[hour]] [[Hour]] values in the Values column of Table 16 Optional field. Present if a Pattern String in [[PatternParts]] contains the substring "{hour}".
    [[minute]] [[Minute]] values in the Values column of Table 16 Optional field. Present if a Pattern String in [[PatternParts]] contains the substring "{minute}".
    [[second]] [[Second]] values in the Values column of Table 16 Optional field. Present if a Pattern String in [[PatternParts]] contains the substring "{second}".
    [[fractionalSecondDigits]] [[FractionalSecondDigits]] values in the Values column of Table 16 Optional field. Present if a Pattern String in [[PatternParts]] contains the substring "{fractionalSecondDigits}".
    [[timeZoneName]] [[TimeZoneName]] values in the Values column of Table 16 Optional field. Present if a Pattern String in [[PatternParts]] contains the substring "{timeZoneName}".
    [[PatternParts]] a List of DateTime Range Pattern Part Records Each record represents a part of the range pattern.

    11.2.3.4 DateTime Range Pattern Part Records

    Each DateTime Range Pattern Part Record has the fields defined in Table 8.

    Table 8: DateTime Range Pattern Part Record
    Field Name Value Type Description
    [[Source]] "shared", "startRange", or "endRange" It indicates which of the range's dates should be formatted using the value of the [[Pattern]] field.
    [[Pattern]] a Pattern String A String of the same format as the regular date pattern String.

    11.2.3.5 DateTime Styles Records

    Each DateTime Styles Record has the fields defined in Table 9.

    Table 9: DateTime Styles Record
    Field Name Value Type
    [[Date]] a DateTime Style Record
    [[Time]] a DateTime Style Record
    [[Connector]] a DateTime Connector Record
    [[DateTimeRangeFormat]] a DateTime Date Range Record

    11.2.3.6 DateTime Style Records

    Each DateTime Style Record has the fields defined in Table 10.

    Table 10: DateTime Style Record
    Field Name Value Type Description
    [[full]] a DateTime Format Record Format record for the "full" style.
    [[long]] a DateTime Format Record Format record for the "long" style.
    [[medium]] a DateTime Format Record Format record for the "medium" style.
    [[short]] a DateTime Format Record Format record for the "short" style.

    11.2.3.7 DateTime Connector Records

    Each DateTime Connector Record has the fields defined in Table 11. All connector pattern strings must contain the strings "{0}" and "{1}".

    Table 11: DateTime Connector Record
    Field Name Value Type Description
    [[full]] a Pattern String Connector pattern when the date style is "full".
    [[long]] a Pattern String Connector pattern when the date style is "long".
    [[medium]] a Pattern String Connector pattern when the date style is "medium".
    [[short]] a Pattern String Connector pattern when the date style is "short".

    11.2.3.8 DateTime Date Range Records

    Each DateTime Date Range Record has the fields defined in Table 12.

    Table 12: DateTime Date Range Record
    Field Name Value Type Description
    [[full]] a DateTime Time Range Record Used when date style is "full".
    [[long]] a DateTime Time Range Record Used when date style is "long".
    [[medium]] a DateTime Time Range Record Used when date style is "medium".
    [[short]] a DateTime Time Range Record Used when date style is "short".

    11.2.3.9 DateTime Time Range Records

    Each DateTime Time Range Record has the fields defined in Table 13.

    Table 13: DateTime Time Range Record
    Field Name Value Type Description
    [[full]] a DateTime Style Range Record Used when time style is "full".
    [[long]] a DateTime Style Range Record Used when time style is "long".
    [[medium]] a DateTime Style Range Record Used when time style is "medium".
    [[short]] a DateTime Style Range Record Used when time style is "short".

    11.2.3.10 DateTime Style Range Records

    Each DateTime Style Range Record has the fields defined in Table 14.

    Table 14: DateTime Style Range Record
    Field Name Value Type Description
    [[rangePatterns]] a DateTime Range Pattern Record Range patterns to combine date and time styles.
    [[rangePatterns12]] a DateTime Range Pattern Record Optional Field. Range patterns to combine date and time styles for 12-hour formats.
    Note 2
    For example, an implementation might include the following Record as part of its English locale data:
    • [[hour]]: "numeric"
    • [[minute]]: "numeric"
    • [[pattern]]: "{hour}:{minute}"
    • [[pattern12]]: "{hour}:{minute} {ampm}"
    • [[rangePatterns]]:
      • [[Hour]]:
        • [[hour]]: "numeric"
        • [[minute]]: "numeric"
        • [[PatternParts]]:
          • {[[Source]]: "startRange", [[Pattern]]: "{hour}:{minute}"}
          • {[[Source]]: "shared", [[Pattern]]: " – "}
          • {[[Source]]: "endRange", [[Pattern]]: "{hour}:{minute}"}
      • [[Minute]]:
        • [[hour]]: "numeric"
        • [[minute]]: "numeric"
        • [[PatternParts]]:
          • {[[Source]]: "startRange", [[Pattern]]: "{hour}:{minute}"}
          • {[[Source]]: "shared", [[Pattern]]: " – "}
          • {[[Source]]: "endRange", [[Pattern]]: "{hour}:{minute}"}
      • [[Default]]:
        • [[year]]: "2-digit"
        • [[month]]: "numeric"
        • [[day]]: "numeric"
        • [[hour]]: "numeric"
        • [[minute]]: "numeric"
        • [[PatternParts]]:
          • {[[Source]]: "startRange", [[Pattern]]: "{day}/{month}/{year}, {hour}:{minute}"}
          • {[[Source]]: "shared", [[Pattern]]: " – "}
          • {[[Source]]: "endRange", [[Pattern]]: "{day}/{month}/{year}, {hour}:{minute}"}
    • [[rangePatterns12]]:
      • [[Hour]]:
        • [[hour]]: "numeric"
        • [[minute]]: "numeric"
        • [[PatternParts]]:
          • {[[Source]]: "startRange", [[Pattern]]: "{hour}:{minute}"}
          • {[[Source]]: "shared", [[Pattern]]: " – "}
          • {[[Source]]: "endRange", [[Pattern]]: "{hour}:{minute}"}
          • {[[Source]]: "shared", [[Pattern]]: " {ampm}"}
      • [[Minute]]:
        • [[hour]]: "numeric"
        • [[minute]]: "numeric"
        • [[PatternParts]]:
          • {[[Source]]: "startRange", [[Pattern]]: "{hour}:{minute}"}
          • {[[Source]]: "shared", [[Pattern]]: " – "}
          • {[[Source]]: "endRange", [[Pattern]]: "{hour}:{minute}"}
          • {[[Source]]: "shared", [[Pattern]]: " {ampm}"}
      • [[Default]]:
        • [[year]]: "2-digit"
        • [[month]]: "numeric"
        • [[day]]: "numeric"
        • [[hour]]: "numeric"
        • [[minute]]: "numeric"
        • [[PatternParts]]:
          • {[[Source]]: "startRange", [[Pattern]]: "{day}/{month}/{year}, {hour}:{minute} {ampm}"}
          • {[[Source]]: "shared", [[Pattern]]: " – "}
          • {[[Source]]: "endRange", [[Pattern]]: "{day}/{month}/{year}, {hour}:{minute} {ampm}"}
     Note 3
    It is recommended that implementations use the locale data provided by the Common Locale Data Repository (available at https://cldr.unicode.org/).

    11.3 Properties of the Intl.DateTimeFormat Prototype Object

    The Intl.DateTimeFormat prototype object:

    • is %Intl.DateTimeFormat.prototype%.
    • is an ordinary object.
    • is not an Intl.DateTimeFormat instance and does not have an [[InitializedDateTimeFormat]] internal slot or any of the other internal slots of Intl.DateTimeFormat instance objects.
    • has a [[Prototype]] internal slot whose value is %Object.prototype%.

    11.3.1 Intl.DateTimeFormat.prototype.constructor

    The initial value of Intl.DateTimeFormat.prototype.constructor is %Intl.DateTimeFormat%.

    11.3.2 Intl.DateTimeFormat.prototype.resolvedOptions ( )

    This function provides access to the locale and options computed during initialization of the object.

    1. Let dtf be the this value.
    2. If the implementation supports the normative optional %Object.prototype%).
    3. For each row of Table 15, except the header row, in table order, do
      1. Let p be the Property value of the current row.
      2. If there is an Internal Slot value in the current row, then
        1. Let v be the value of dtf's internal slot whose name is the Internal Slot value of the current row.
      3. Else,
        1. Let format be dtf.[[DateTimeFormat]].
        2. If format has a field [[<p>]] and dtf.[[DateStyle]] is undefined and dtf.[[TimeStyle]] is undefined, then
          1. Let v be format.[[<p>]].
        3. Else,
          1. Let v be undefined.
      4. If v is not undefined, then
        1. If there is a Conversion value in the current row, then
          1. Let conversion be the Conversion value of the current row.
          2. If conversion is hour12, then
            1. If v is "h11" or "h12", set v to true. Otherwise, set v to false.
          3. Else,
            1. CreateDataPropertyOrThrow(options, p, v).
        2. Return options.
        Table 15: Resolved Options of DateTimeFormat Instances
        Internal Slot Property Conversion
        [[Locale]] "locale"
        [[Calendar]] "calendar"
        [[NumberingSystem]] "numberingSystem"
        [[TimeZone]] "timeZone"
        [[HourCycle]] "hourCycle"
        [[HourCycle]] "hour12" hour12
        "weekday"
        "era"
        "year"
        "month"
        "day"
        "dayPeriod"
        "hour"
        "minute"
        "second"
        "fractionalSecondDigits" number
        "timeZoneName"
        [[DateStyle]] "dateStyle"
        [[TimeStyle]] "timeStyle"

        For web compatibility reasons, if the property "hourCycle" is set, the "hour12" property should be set to true when "hourCycle" is "h11" or "h12", or to false when "hourCycle" is "h23" or "h24".

        Note 1
        In this version of the API, the "timeZone" property will be the identifier of the constructor. The first edition left the "timeZone" property undefined in this case.
        Note 2
        For compatibility with versions prior to the fifth edition, the "hour12" property is set in addition to the "hourCycle" property.

        11.3.3 get Intl.DateTimeFormat.prototype.format

        Intl.DateTimeFormat.prototype.format is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

        1. Let dtf be the this value.
        2. If the implementation supports the normative optional function object as defined in DateTime Format Functions (11.5.4).
        3. Set F.[[DateTimeFormat]] to dtf.
        4. Set dtf.[[BoundFormat]] to F.
      5. Return dtf.[[BoundFormat]].
      Note
      The returned function is bound to dtf so that it can be passed directly to Array.prototype.map or other functions. This is considered a historical artefact, as part of a convention which is no longer followed for new features, but is preserved to maintain compatibility with existing programs.

      11.3.4 Intl.DateTimeFormat.prototype.formatRange ( startDate, endDate )

      When the formatRange method is called with arguments startDate and endDate, the following steps are taken:

      1. Let dtf be this value.
      2. Perform ? ToNumber(endDate).
      3. Return ? FormatDateTimeRange(dtf, x, y).

      11.3.5 Intl.DateTimeFormat.prototype.formatRangeToParts ( startDate, endDate )

      When the formatRangeToParts method is called with arguments startDate and endDate, the following steps are taken:

      1. Let dtf be this value.
      2. Perform ? ToNumber(endDate).
      3. Return ? FormatDateTimeRangeToParts(dtf, x, y).

      11.3.6 Intl.DateTimeFormat.prototype.formatToParts ( date )

      When the formatToParts method is called with an argument date, the following steps are taken:

      1. Let dtf be the this value.
      2. Perform ? ToNumber(date).
    4. Return ? FormatDateTimeToParts(dtf, x).

    11.3.7 Intl.DateTimeFormat.prototype [ %Symbol.toStringTag% ]

    The initial value of the %Symbol.toStringTag% property is the String value "Intl.DateTimeFormat".

    This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

    11.4 Properties of Intl.DateTimeFormat Instances

    Intl.DateTimeFormat instances are ordinary objects that inherit properties from %Intl.DateTimeFormat.prototype%.

    Intl.DateTimeFormat instances have an [[InitializedDateTimeFormat]] internal slot.

    Intl.DateTimeFormat instances also have several internal slots that are computed by The Intl.DateTimeFormat Constructor:

    • [[Locale]] is a String value with the language tag of the locale whose localization is used for formatting.
    • [[Calendar]] Unicode Calendar Identifier used for formatting.
    • [[NumberingSystem]] Unicode Number System Identifier used for formatting.
    • [[TimeZone]] offset time zone identifier.
    • [[HourCycle]] is a String value indicating whether the 12-hour format ("h11", "h12") or the 24-hour format ("h23", "h24") should be used. "h11" and "h23" start with hour 0 and go up to 11 and 23 respectively. "h12" and "h24" start with hour 1 and go up to 12 and 24. [[HourCycle]] is only used when [[DateTimeFormat]] has an [[hour]] field.
    • [[DateStyle]], [[TimeStyle]] are each either undefined, or a String value with values "full", "long", "medium", or "short".
    • [[DateTimeFormat]] is a DateTime Format Record.

    Finally, Intl.DateTimeFormat instances have a [[BoundFormat]] internal slot that caches the function returned by the format accessor (11.3.3).

    11.5 Abstract Operations for DateTimeFormat Objects

    Several DateTimeFormat algorithms use values from the following table, which provides internal slots, property names and allowable values for the components of date and time formats:

    Table 16: Components of date and time formats
    Field Name Property Values
    [[Weekday]] "weekday" "narrow", "short", "long"
    [[Era]] "era" "narrow", "short", "long"
    [[Year]] "year" "2-digit", "numeric"
    [[Month]] "month" "2-digit", "numeric", "narrow", "short", "long"
    [[Day]] "day" "2-digit", "numeric"
    [[DayPeriod]] "dayPeriod" "narrow", "short", "long"
    [[Hour]] "hour" "2-digit", "numeric"
    [[Minute]] "minute" "2-digit", "numeric"
    [[Second]] "second" "2-digit", "numeric"
    [[FractionalSecondDigits]] "fractionalSecondDigits" 1, 2, 3
    [[TimeZoneName]] "timeZoneName" "short", "long", "shortOffset", "longOffset", "shortGeneric", "longGeneric"

    11.5.1 DateTimeStyleFormat ( dateStyle, timeStyle, styles )

    The abstract operation DateTimeStyleFormat takes arguments dateStyle ("full", "long", "medium", "short", or undefined), timeStyle ("full", "long", "medium", "short", or undefined), and styles (a DateTime Styles Record) and returns a DateTime Format Record. styles is a Record for date time formatting based on the parameters. It performs the following steps when called:

    1. substring "{0}" replaced with timeFormat.[[pattern]] and the Assert: dateStyle is not undefined.
    2. Return dateFormat.

    11.5.2 BasicFormatMatcher ( options, formats )

    The abstract operation BasicFormatMatcher takes arguments options (a List of DateTime Format Records) and returns a DateTime Format Record. It performs the following steps when called:

    1. Let removalPenalty be 120.
    2. Let additionPenalty be 20.
    3. Let longLessPenalty be 8.
    4. Let longMorePenalty be 6.
    5. Let shortLessPenalty be 6.
    6. Let shortMorePenalty be 3.
    7. Let offsetPenalty be 1.
    8. Let bestScore be -∞.
    9. Let bestFormat be undefined.
    10. For each element format of formats, do
      1. Let score be 0.
      2. For each row of Table 16, except the header row, in table order, do
        1. Let property be the name given in the Property column of the current row.
        2. If options has a field [[<property>]], let optionsProp be options.[[<property>]]; else let optionsProp be undefined.
        3. If format has a field [[<property>]], let formatProp be format.[[<property>]]; else let formatProp be undefined.
        4. If optionsProp is undefined and formatProp is not undefined, then
          1. Set score to score - additionPenalty.
        5. Else if optionsProp is not undefined and formatProp is undefined, then
          1. Set score to score - removalPenalty.
        6. Else if property is "timeZoneName", then
          1. If optionsProp is "short" or "shortGeneric", then
            1. If formatProp is "shortOffset", set score to score - offsetPenalty.
            2. Else if formatProp is "longOffset", set score to score - (offsetPenalty + shortMorePenalty).
            3. Else if optionsProp is "short" and formatProp is "long", set score to score - shortMorePenalty.
            4. Else if optionsProp is "shortGeneric" and formatProp is "longGeneric", set score to score - shortMorePenalty.
            5. Else if optionsProp ≠ formatProp, set score to score - removalPenalty.
          2. Else if optionsProp is "shortOffset" and formatProp is "longOffset", then
            1. Set score to score - shortMorePenalty.
          3. Else if optionsProp is "long" or "longGeneric", then
            1. If formatProp is "longOffset", set score to score - offsetPenalty.
            2. Else if formatProp is "shortOffset", set score to score - (offsetPenalty + longLessPenalty).
            3. Else if optionsProp is "long" and formatProp is "short", set score to score - longLessPenalty.
            4. Else if optionsProp is "longGeneric" and formatProp is "shortGeneric", set score to score - longLessPenalty.
            5. Else if optionsProp ≠ formatProp, set score to score - removalPenalty.
          4. Else if optionsProp is "longOffset" and formatProp is "shortOffset", then
            1. Set score to score - longLessPenalty.
          5. Else if optionsProp ≠ formatProp, then
            1. Set score to score - removalPenalty.
        7. Else if optionsProp ≠ formatProp, then
          1. If property is "fractionalSecondDigits", then
            1. Let values be « 1, 2, 3 ».
          2. Else,
            1. Let values be « "2-digit", "numeric", "narrow", "short", "long" ».
          3. Let optionsPropIndex be the index of optionsProp within values.
          4. Let formatPropIndex be the index of formatProp within values.
          5. Let delta be min(formatPropIndex - optionsPropIndex, 2), -2).
          6. If delta = 2, set score to score - longMorePenalty.
          7. Else if delta = 1, set score to score - shortMorePenalty.
          8. Else if delta = -1, set score to score - shortLessPenalty.
          9. Else if delta = -2, set score to score - longLessPenalty.
      3. If score > bestScore, then
        1. Set bestScore to score.
        2. Set bestFormat to format.
    11. Return bestFormat.

    11.5.3 BestFitFormatMatcher ( options, formats )

    The List of DateTime Format Records) and returns a DateTime Format Record. It returns a set of component representations that a typical user of the selected locale would perceive as at least as good as the one returned by BasicFormatMatcher.

    11.5.4 DateTime Format Functions

    A DateTime format function is an anonymous built-in function that has a [[DateTimeFormat]] internal slot.

    When a DateTime format function F is called with optional argument date, the following steps are taken:

    1. Let dtf be F.[[DateTimeFormat]].
    2. ToNumber(date).
  • Return ? FormatDateTime(dtf, x).
    •

    The "length" property of a DateTime format function is 1𝔽.

    11.5.5 FormatDateTimePattern ( dateTimeFormat, format, pattern, epochNanoseconds )

    The abstract operation FormatDateTimePattern takes arguments dateTimeFormat (an Intl.DateTimeFormat), format (a DateTime Format Record or a DateTime Range Pattern Format Record), pattern (a Pattern String), and epochNanoseconds (a BigInt) and returns a epoch time epochNanoseconds according to pattern and to the effective locale and the formatting options of dateTimeFormat and format. It performs the following steps when called:

    1. Let locale be dateTimeFormat.[[Locale]].
    2. Let nfOptions be Construct(%Intl.NumberFormat%, « locale, nfOptions »).
    3. Let nf2Options be CreateDataPropertyOrThrow(nf2Options, "useGrouping", false).
    4. Let nf2 be ! 𝔽(fractionalSecondDigits)).
    5. Perform ! List.
    6. For each floor(v × 10( fractionalSecondDigits - 3 )).
    7. Let fv be FormatNumeric(nf3, v).
    8. Append the Assert: format has a field [[timeZoneName]].
    9. Let f be format.[[timeZoneName]].
    10. Let v be dateTimeFormat.[[TimeZone]].
    11. Let fv be a String value representing v in the form given by f; the String value depends upon the implementation and the effective locale of dateTimeFormat. The String value may also depend on the value of the [[InDST]] field of tm if f is "short", "long", "shortOffset", or "longOffset". If the implementation does not have such a localized representation of f, then use the String value of v itself.
    12. Append the StringToCodePoints(fv).
    13. Let count be the number of elements in codePoints.
    14. If count > 2, then
      1. Let tens be codePoints[count - 2].
      2. Let ones be codePoints[count - 1].
      3. Set fv to Record { [[Type]]: "relatedYear", [[Value]]: fv } to result.
    15. Else if p is "yearName", then
      1. Let v be tm.[[YearName]].
      2. Let fv be an ILD String value representing v.
      3. Append the Record { [[Type]]: "unknown", [[Value]]: unknown } to result.
  • Return result.
    •  Note
    It is recommended that implementations use the locale and calendar dependent strings provided by the Common Locale Data Repository (available at https://cldr.unicode.org/), and use CLDR "abbreviated" strings for DateTimeFormat "short" strings, and CLDR "wide" strings for DateTimeFormat "long" strings.

    11.5.6 PartitionDateTimePattern ( dateTimeFormat, x )

    The abstract operation PartitionDateTimePattern takes arguments dateTimeFormat (an Intl.DateTimeFormat) and x (a Number) and returns either a throw completion. It interprets x as a 21.4.1.1, and creates the corresponding parts according to the effective locale and the formatting options of dateTimeFormat. It performs the following steps when called:

    1. Let x be ℝ(x) × 106).
    2. Let format be dateTimeFormat.[[DateTimeFormat]].
    3. If dateTimeFormat.[[HourCycle]] is "h11" or "h12", then
      1. Let pattern be format.[[pattern12]].
    4. Else,
      1. Let pattern be format.[[pattern]].
    5. Let result be FormatDateTimePattern(dateTimeFormat, format, pattern, epochNanoseconds).
    6. Return result.

    11.5.7 FormatDateTime ( dateTimeFormat, x )

    The abstract operation FormatDateTime takes arguments dateTimeFormat (an Intl.DateTimeFormat) and x (a Number) and returns either a throw completion. It performs the following steps when called:

    1. Let parts be ? PartitionDateTimePattern(dateTimeFormat, x).
    2. Let result be the empty String.
    3. For each string-concatenation of result and part.[[Value]].
  • Return result.
    •

    11.5.8 FormatDateTimeToParts ( dateTimeFormat, x )

    The abstract operation FormatDateTimeToParts takes arguments dateTimeFormat (an Intl.DateTimeFormat) and x (a Number) and returns either a throw completion. It performs the following steps when called:

    1. Let parts be ? PartitionDateTimePattern(dateTimeFormat, x).
    2. Let result be ! %Object.prototype%).
    3. Perform ! ToString(𝔽(n)), O).
    4. Increment n by 1.
  • Return result.
    •

    11.5.9 PartitionDateTimeRangePattern ( dateTimeFormat, x, y )

    The abstract operation PartitionDateTimeRangePattern takes arguments dateTimeFormat (an Intl.DateTimeFormat), x (a Number), and y (a Number) and returns either a throw completion. It interprets x and y as 21.4.1.1, and creates the corresponding parts according to the effective locale and the formatting options of dateTimeFormat. It performs the following steps when called:

    1. Set x to ℝ(x) × 106).
    2. Let yEpochNanoseconds be floor(tm2.[[Millisecond]] × 10exp).
  • Else,
    1. Let v1 be tm1's field whose name is fieldName.
    2. Let v2 be tm2's field whose name is fieldName.
  • If v1 is not equal to v2, then
    1. Set relevantFieldsEqual to false.
  • If relevantFieldsEqual is true, then
    1. Let collapsedResult be a new empty List.
    2. If selectedRangePattern is undefined, then
      1. Set selectedRangePattern to rangePatterns.[[Default]].
    3. For each Record { [[Type]]: r.[[Type]], [[Value]]: r.[[Value]], [[Source]]: source } to rangeResult.
  • Return rangeResult.
    •

    11.5.10 FormatDateTimeRange ( dateTimeFormat, x, y )

    The abstract operation FormatDateTimeRange takes arguments dateTimeFormat (an Intl.DateTimeFormat), x (a Number), and y (a Number) and returns either a throw completion. It performs the following steps when called:

    1. Let parts be ? PartitionDateTimeRangePattern(dateTimeFormat, x, y).
    2. Let result be the empty String.
    3. For each string-concatenation of result and part.[[Value]].
  • Return result.
    •

    11.5.11 FormatDateTimeRangeToParts ( dateTimeFormat, x, y )

    The abstract operation FormatDateTimeRangeToParts takes arguments dateTimeFormat (an Intl.DateTimeFormat), x (a Number), and y (a Number) and returns either a throw completion. It performs the following steps when called:

    1. Let parts be ? PartitionDateTimeRangePattern(dateTimeFormat, x, y).
    2. Let result be ! %Object.prototype%).
    3. Perform ! CreateDataPropertyOrThrow(result, ! 𝔽(n)), O).
    4. Increment n by 1.
  • Return result.
    •

    11.5.12 ToLocalTime ( epochNs, calendar, timeZoneIdentifier )

    The implementation-defined abstract operation ToLocalTime takes arguments epochNs (a BigInt), calendar (a String), and timeZoneIdentifier (a String) and returns a ToLocalTime Record. It performs the following steps when called:

    1. If GetNamedTimeZoneOffsetNanoseconds(timeZoneIdentifier, epochNs).
  • Let tz be ℝ(epochNs) + offsetNs.
  • If calendar is "gregory", then
    1. Return a ToLocalTime Record with fields calculated from tz according to Table 17.
  • Else,
    1. Return a ToLocalTime Record with the fields calculated from tz for the given calendar. The calculations should use best available information about the specified calendar.
    •

    11.5.13 ToLocalTime Records

    Each ToLocalTime Record has the fields defined in Table 17.

    Table 17: Record returned by ToLocalTime
    Field Name Value Type Value Calculation for Gregorian Calendar
    [[Weekday]] an integer floor(tz / 106))))
    [[Era]] a String Let year be floor(tz / 106))). If year < 1𝔽, return "BC", else return "AD".
    [[Year]] an integer floor(tz / 106))))
    [[RelatedYear]] an integer or undefined undefined
    [[YearName]] a String or undefined undefined
    [[Month]] an integer floor(tz / 106))))
    [[Day]] an integer floor(tz / 106))))
    [[Hour]] an integer floor(tz / 106))))
    [[Minute]] an integer floor(tz / 106))))
    [[Second]] an integer floor(tz / 106))))
    [[Millisecond]] an integer floor(tz / 106))))
    [[InDST]] a Boolean Calculate true or false using the best available information about the specified calendar and timeZoneIdentifier, including current and historical information from the IANA Time Zone Database about time zone offsets from UTC and daylight saving time rules.
    Normative Optional

    11.5.14 UnwrapDateTimeFormat ( dtf )

    The abstract operation UnwrapDateTimeFormat takes argument dtf (an throw completion. It returns the DateTimeFormat instance of its input object, which is either the value itself or a value associated with it by %Intl.DateTimeFormat% according to the normative optional constructor mode of 4.3 Note 1. It performs the following steps when called:

    1. If dtf Get(dtf, %Intl%.[[FallbackSymbol]]).
  • Return dtf.
    •

    12 DisplayNames Objects

    12.1 The Intl.DisplayNames Constructor

    The Intl.DisplayNames constructor:

    • is %Intl.DisplayNames%.
    • is the initial value of the "DisplayNames" property of the Intl object.

    Behaviour common to all service constructor properties of the Intl object is specified in 9.1.

    12.1.1 Intl.DisplayNames ( locales, options )

    When the Intl.DisplayNames function is called with arguments locales and options, the following steps are taken:

    1. If NewTarget is undefined, throw a TypeError exception.
    2. Let displayNames be ? Assert: typeFields is a Assert: styleFields is a Record (see 12.2.3).
    3. Set displayNames.[[Fields]] to styleFields.
    4. Return displayNames.

    12.2 Properties of the Intl.DisplayNames Constructor

    The Intl.DisplayNames constructor:

    • has a [[Prototype]] internal slot whose value is %Function.prototype%.
    • has the following properties:

    12.2.1 Intl.DisplayNames.prototype

    The value of Intl.DisplayNames.prototype is %Intl.DisplayNames.prototype%.

    This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.

    12.2.2 Intl.DisplayNames.supportedLocalesOf ( locales [ , options ] )

    When the supportedLocalesOf method is called with arguments locales and options, the following steps are taken:

    1. Let availableLocales be %Intl.DisplayNames%.[[AvailableLocales]].
    2. Let requestedLocales be ? CanonicalizeLocaleList(locales).
    3. Return ? FilterLocales(availableLocales, requestedLocales, options).

    12.2.3 Internal slots

    The value of the [[AvailableLocales]] internal slot is implementation-defined within the constraints described in 9.1.

    The value of the [[RelevantExtensionKeys]] internal slot is « ».

    The value of the [[ResolutionOptionDescriptors]] internal slot is « ».

    The value of the [[LocaleData]] internal slot is implementation-defined within the constraints described in 9.1 and the following additional constraints:

    • [[LocaleData]].[[<locale>]] must have a [[types]] field for all locale values locale. The value of this field must be a Record, which must have fields with the names of all display name types: "language", "region", "script", "currency", "calendar", and "dateTimeField".
    • The value of the field "language" must be a Record which must have fields with the names of one of the valid language displays: "dialect" and "standard".
    • The language display fields under display name type "language" should contain Records which must have fields with the names of one of the valid display name styles: "narrow", "short", and "long".
    • The value of the fields "region", "script", "currency", "calendar", and "dateTimeField" must be Records, which must have fields with the names of all display name styles: "narrow", "short", and "long".
    • The display name style fields under display name type "language" should contain Records with keys corresponding to language codes that can be matched by the unicode_language_id Unicode locale nonterminal. The value of these fields must be string values.
    • The display name style fields under display name type "region" should contain Records with keys corresponding to region codes. The value of these fields must be string values.
    • The display name style fields under display name type "script" should contain Records with keys corresponding to script codes. The value of these fields must be string values.
    • The display name style fields under display name type "currency" should contain Records with keys corresponding to currency codes. The value of these fields must be string values.
    • The display name style fields under display name type "calendar" should contain Records with keys corresponding to calendar identifiers that can be matched by the type Unicode locale nonterminal. The value of these fields must be string values.
    • The display name style fields under display name type "dateTimeField" should contain Records with keys corresponding to codes listed in Table 19. The value of these fields must be string values.
    Note
    It is recommended that implementations use the locale data provided by the Common Locale Data Repository (available at https://cldr.unicode.org/).

    12.3 Properties of the Intl.DisplayNames Prototype Object

    The Intl.DisplayNames prototype object:

    • is %Intl.DisplayNames.prototype%.
    • is an ordinary object.
    • is not an Intl.DisplayNames instance and does not have an [[InitializedDisplayNames]] internal slot or any of the other internal slots of Intl.DisplayNames instance objects.
    • has a [[Prototype]] internal slot whose value is %Object.prototype%.

    12.3.1 Intl.DisplayNames.prototype.constructor

    The initial value of Intl.DisplayNames.prototype.constructor is %Intl.DisplayNames%.

    12.3.2 Intl.DisplayNames.prototype.resolvedOptions ( )

    This function provides access to the locale and options computed during initialization of the object.

    1. Let displayNames be this value.
    2. Perform ? Assert: v is not undefined.
    3. Perform ! CreateDataPropertyOrThrow(options, p, v).
  • Return options.
    •
    Table 18: Resolved Options of DisplayNames Instances
    Internal Slot Property
    [[Locale]] "locale"
    [[Style]] "style"
    [[Type]] "type"
    [[Fallback]] "fallback"
    [[LanguageDisplay]] "languageDisplay"

    12.3.3 Intl.DisplayNames.prototype.of ( code )

    When the Intl.DisplayNames.prototype.of is called with an argument code, the following steps are taken:

    1. Let displayNames be this value.
    2. Perform ? ToString(code).
    3. Set code to ? CanonicalCodeForDisplayNames(displayNames.[[Type]], code).
    4. Let fields be displayNames.[[Fields]].
    5. If fields has a field [[<code>]], return fields.[[<code>]].
    6. If displayNames.[[Fallback]] is "code", return code.
    7. Return undefined.

    12.3.4 Intl.DisplayNames.prototype [ %Symbol.toStringTag% ]

    The initial value of the %Symbol.toStringTag% property is the String value "Intl.DisplayNames".

    This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

    12.4 Properties of Intl.DisplayNames Instances

    Intl.DisplayNames instances are ordinary objects that inherit properties from %Intl.DisplayNames.prototype%.

    Intl.DisplayNames instances have an [[InitializedDisplayNames]] internal slot.

    Intl.DisplayNames instances also have several internal slots that are computed by The Intl.DisplayNames Constructor:

    • [[Locale]] is a String value with the language tag of the locale whose localization is used for formatting.
    • [[Style]] is one of the String values "narrow", "short", or "long", identifying the display name style used.
    • [[Type]] is one of the String values "language", "region", "script", "currency", "calendar", or "dateTimeField", identifying the type of the display names requested.
    • [[Fallback]] is one of the String values "code" or "none", identifying the fallback return when the system does not have the requested display name.
    • [[LanguageDisplay]] is one of the String values "dialect" or "standard", identifying the language display kind. It is only used when [[Type]] has the value "language".
    • [[Fields]] is a Record (see 12.2.3) which must have fields with keys corresponding to codes according to [[Style]], [[Type]], and [[LanguageDisplay]].

    12.5 Abstract Operations for DisplayNames Objects

    12.5.1 CanonicalCodeForDisplayNames ( type, code )

    The abstract operation CanonicalCodeForDisplayNames takes arguments type (a String) and code (a String) and returns either a throw completion. It verifies that code represents a well-formed code according to type and returns the case-regularized form of code. It performs the following steps when called:

    1. If type is "language", then
      1. If code cannot be matched by the unicode_language_id Unicode locale nonterminal, throw a RangeError exception.
      2. If IsStructurallyValidLanguageTag(code) is false, throw a RangeError exception.
      3. Return CanonicalizeUnicodeLocaleId(code).
    2. If type is "region", then
      1. If code cannot be matched by the unicode_region_subtag Unicode locale nonterminal, throw a RangeError exception.
      2. Return the ASCII-uppercase of code.
    3. If type is "script", then
      1. If code cannot be matched by the unicode_script_subtag Unicode locale nonterminal, throw a RangeError exception.
      2. string-concatenation of first and rest.
    4. If type is "calendar", then
      1. If code cannot be matched by the type Unicode locale nonterminal, throw a RangeError exception.
      2. If code uses any of the backwards compatibility syntax described in Assert: type is "currency".
      3. If IsWellFormedCurrencyCode(code) is false, throw a RangeError exception.
      4. Return the ASCII-uppercase of code.

      12.5.2 IsValidDateTimeFieldCode ( field )

      The abstract operation IsValidDateTimeFieldCode takes argument field (a String) and returns a Boolean. It verifies that the field argument represents a valid date time field code. It performs the following steps when called:

      1. If field is listed in the Code column of Table 19, return true.
      2. Return false.
      Table 19: Codes For Date Time Field of DisplayNames
      Code Description
      "era" The field indicating the era, e.g. AD or BC in the Gregorian or Julian calendar.
      "year" The field indicating the year (within an era).
      "quarter" The field indicating the quarter, e.g. Q2, 2nd quarter, etc.
      "month" The field indicating the month, e.g. Sep, September, etc.
      "weekOfYear" The field indicating the week number within a year.
      "weekday" The field indicating the day of week, e.g. Tue, Tuesday, etc.
      "day" The field indicating the day in month.
      "dayPeriod" The field indicating the day period, either am, pm, etc. or noon, evening, etc..
      "hour" The field indicating the hour.
      "minute" The field indicating the minute.
      "second" The field indicating the second.
      "timeZoneName" The field indicating the time zone name, e.g. PDT, Pacific Daylight Time, etc.

      13 DurationFormat Objects

      13.1 The Intl.DurationFormat Constructor

      The Intl.DurationFormat constructor:

      • is %Intl.DurationFormat%.
      • is the initial value of the "DurationFormat" property of the Intl object.

      Behaviour common to all service constructor properties of the Intl object is specified in 9.1.

      13.1.1 Intl.DurationFormat ( [ locales [ , options ] ] )

      When the Intl.DurationFormat function is called with optional arguments locales and options, the following steps are taken:

      1. If NewTarget is undefined, throw a TypeError exception.
      2. Let durationFormat be ? OrdinaryCreateFromConstructor(NewTarget, "%Intl.DurationFormatPrototype%", « [[InitializedDurationFormat]], [[Locale]], [[NumberingSystem]], [[Style]], [[YearsOptions]], [[MonthsOptions]], [[WeeksOptions]], [[DaysOptions]], [[HoursOptions]], [[MinutesOptions]], [[SecondsOptions]], [[MillisecondsOptions]], [[MicrosecondsOptions]], [[NanosecondsOptions]], [[HourMinuteSeparator]], [[MinuteSecondSeparator]], [[FractionalDigits]] »).
      3. Let optionsResolution be ? ResolveOptions(%Intl.DurationFormat%, %Intl.DurationFormat%.[[LocaleData]], locales, options).
      4. Set options to optionsResolution.[[Options]].
      5. Let r be optionsResolution.[[ResolvedLocale]].
      6. Set durationFormat.[[Locale]] to r.[[Locale]].
      7. Let resolvedLocaleData be r.[[LocaleData]].
      8. Let digitalFormat be resolvedLocaleData.[[DigitalFormat]].
      9. Set durationFormat.[[HourMinuteSeparator]] to digitalFormat.[[HourMinuteSeparator]].
      10. Set durationFormat.[[MinuteSecondSeparator]] to digitalFormat.[[MinuteSecondSeparator]].
      11. Set durationFormat.[[NumberingSystem]] to r.[[nu]].
      12. Let style be ? GetOption(options, "style", string, « "long", "short", "narrow", "digital" », "short").
      13. Set durationFormat.[[Style]] to style.
      14. Let prevStyle be the empty String.
      15. For each row of Table 20, except the header row, in table order, do
        1. Let slot be the Internal Slot value of the current row.
        2. Let unit be the Unit value of the current row.
        3. Let styles be the Styles value of the current row.
        4. Let digitalBase be the Digital Default value of the current row.
        5. Let unitOptions be ? GetDurationUnitOptions(unit, options, style, styles, digitalBase, prevStyle, digitalFormat.[[TwoDigitHours]]).
        6. Set the value of durationFormat's internal slot whose name is slot to unitOptions.
        7. If unit is one of "hours", "minutes", "seconds", "milliseconds", or "microseconds", then
          1. Set prevStyle to unitOptions.[[Style]].
      16. Set durationFormat.[[FractionalDigits]] to ? GetNumberOption(options, "fractionalDigits", 0, 9, undefined).
      17. Return durationFormat.
      Table 20: Internal slots and property names of DurationFormat instances
      Internal Slot Unit Styles Digital Default
      [[YearsOptions]] "years" « "long", "short", "narrow" » "short"
      [[MonthsOptions]] "months" « "long", "short", "narrow" » "short"
      [[WeeksOptions]] "weeks" « "long", "short", "narrow" » "short"
      [[DaysOptions]] "days" « "long", "short", "narrow" » "short"
      [[HoursOptions]] "hours" « "long", "short", "narrow", "numeric", "2-digit" » "numeric"
      [[MinutesOptions]] "minutes" « "long", "short", "narrow", "numeric", "2-digit" » "numeric"
      [[SecondsOptions]] "seconds" « "long", "short", "narrow", "numeric", "2-digit" » "numeric"
      [[MillisecondsOptions]] "milliseconds" « "long", "short", "narrow", "numeric" » "numeric"
      [[MicrosecondsOptions]] "microseconds" « "long", "short", "narrow", "numeric" » "numeric"
      [[NanosecondsOptions]] "nanoseconds" « "long", "short", "narrow", "numeric" » "numeric"

      13.2 Properties of the Intl.DurationFormat Constructor

      The Intl.DurationFormat constructor:

      • has a [[Prototype]] internal slot whose value is %Function.prototype%.
      • has the following properties:

      13.2.1 Intl.DurationFormat.prototype

      The value of Intl.DurationFormat.prototype is %Intl.DurationFormat.prototype%.

      This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.

      13.2.2 Intl.DurationFormat.supportedLocalesOf ( locales [ , options ] )

      When the supportedLocalesOf method is called with arguments locales and options, the following steps are taken:

      1. Let availableLocales be %Intl.DurationFormat%.[[AvailableLocales]].
      2. Let requestedLocales be ? CanonicalizeLocaleList(locales).
      3. Return ? FilterLocales(availableLocales, requestedLocales, options).

      13.2.3 Internal slots

      The value of the [[AvailableLocales]] internal slot is implementation defined within the constraints described in 9.1.

      The value of the [[RelevantExtensionKeys]] internal slot is « "nu" ».

      The value of the [[ResolutionOptionDescriptors]] internal slot is « { [[Key]]: "nu", [[Property]]: "numberingSystem" } ».

      The value of the [[LocaleData]] internal slot is implementation-defined within the constraints described in 9.1 and the following additional constraints for all locale values locale:

      • [[LocaleData]].[[<locale>]] must be a Record with fields [[nu]] and [[DigitalFormat]].
      • [[LocaleData]].[[<locale>]].[[nu]] must be a List as specified in 16.2.3 and must not include the values "native", "traditio", or "finance".
      • [[LocaleData]].[[<locale>]].[[DigitalFormat]] must be a Record containing the following fields:
        • [[HourMinuteSeparator]] must be a String value that is the appropriate separator between hours and minutes for that combination of locale and numbering system when using style "numeric" or "2-digit".
        • [[MinuteSecondSeparator]] must be a String value that is the appropriate separator between minutes and seconds for that combination of locale and numbering system when using style "numeric" or "2-digit".
        • [[TwoDigitHours]] must be a Boolean value indicating whether hours are always displayed using two digits when using style "numeric".
      Note
      It is recommended that implementations use the locale data provided by the Common Locale Data Repository (available at http://cldr.unicode.org/).

      13.3 Properties of the Intl.DurationFormat Prototype Object

      The Intl.DurationFormat prototype object:

      • is %Intl.DurationFormat.prototype%.
      • is an ordinary object.
      • is not an Intl.DurationFormat instance and does not have an [[InitializedDurationFormat]] internal slot or any of the other internal slots of Intl.DurationFormat instance objects.
      • has a [[Prototype]] internal slot whose value is %Object.prototype%.

      13.3.1 Intl.DurationFormat.prototype.constructor

      The initial value of Intl.DurationFormat.prototype.constructor is the intrinsic object %Intl.DurationFormat%.

      13.3.2 Intl.DurationFormat.prototype.resolvedOptions ( )

      This function provides access to the locale and options computed during initialization of the object.

      1. Let df be the this value.
      2. Perform ? 𝔽(v).
    5. Else if conversion is not empty, then
      1. string-concatenation of p and "Display".
      2. Set v to v.[[Display]].
    6. Perform ! CreateDataPropertyOrThrow(options, p, v).
  • Return options.
    •
    Table 21: Resolved Options of DurationFormat Instances
    Internal Slot Property Conversion
    [[Locale]] "locale"
    [[NumberingSystem]] "numberingSystem"
    [[Style]] "style"
    [[YearsOptions]] "years" style+display
    [[MonthsOptions]] "months" style+display
    [[WeeksOptions]] "weeks" style+display
    [[DaysOptions]] "days" style+display
    [[HoursOptions]] "hours" style+display
    [[MinutesOptions]] "minutes" style+display
    [[SecondsOptions]] "seconds" style+display
    [[MillisecondsOptions]] "milliseconds" style+display
    [[MicrosecondsOptions]] "microseconds" style+display
    [[NanosecondsOptions]] "nanoseconds" style+display
    [[FractionalDigits]] "fractionalDigits" number

    13.3.3 Intl.DurationFormat.prototype.format ( duration )

    When the format method is called with an argument duration, the following steps are taken:

    1. Let df be the this value.
    2. Perform ? string-concatenation of result and part.[[Value]].
  • Return result.
    •

    13.3.4 Intl.DurationFormat.prototype.formatToParts ( duration )

    When the formatToParts method is called with an argument duration, the following steps are taken:

    1. Let df be the this value.
    2. Perform ? OrdinaryObjectCreate(CreateDataPropertyOrThrow(obj, "unit", part.[[Unit]]).
    3. Perform ! ToString(n), obj).
    4. Set n to n + 1.
  • Return result.
    •

    13.3.5 Intl.DurationFormat.prototype [ %Symbol.toStringTag% ]

    The initial value of the %Symbol.toStringTag% property is the String value "Intl.DurationFormat".

    This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

    13.4 Properties of Intl.DurationFormat Instances

    Intl.DurationFormat instances inherit properties from %Intl.DurationFormat.prototype%.

    Intl.DurationFormat instances have an [[InitializedDurationFormat]] internal slot.

    Intl.DurationFormat instances also have several internal slots that are computed by The Intl.DurationFormat Constructor:

    13.5 Abstract Operations for DurationFormat Objects

    13.5.1 Duration Records

    A Duration Record is a Record value used to represent a Duration.

    Duration Records have the fields listed in Table 22

    Table 22: Duration Record Fields
    Field Meaning
    [[Years]] The number of years in the duration.
    [[Months]] The number of months in the duration.
    [[Weeks]] The number of weeks in the duration.
    [[Days]] The number of days in the duration.
    [[Hours]] The number of hours in the duration.
    [[Minutes]] The number of minutes in the duration.
    [[Seconds]] The number of seconds in the duration.
    [[Milliseconds]] The number of milliseconds in the duration.
    [[Microseconds]] The number of microseconds in the duration.
    [[Nanoseconds]] The number of nanoseconds in the duration.

    13.5.2 ToIntegerIfIntegral ( argument )

    The abstract operation ToIntegerIfIntegral takes argument argument (an throw completion. It converts argument to an integral. It performs the following steps when called:

    1. Let number be ? ℝ(number).

    13.5.3 ToDurationRecord ( input )

    The abstract operation ToDurationRecord takes argument input (an throw completion. It converts a given object that represents a Duration into a Duration Record. It performs the following steps when called:

    1. If input Get(input, "hours").
    2. If hours is not undefined, set result.[[Hours]] to ? ToIntegerIfIntegral(hours).
    3. Let microseconds be ? Get(input, "months").
    4. If months is not undefined, set result.[[Months]] to ? ToIntegerIfIntegral(months).
    5. Let nanoseconds be ? Get(input, "years").
    6. If years is not undefined, set result.[[Years]] to ? ToIntegerIfIntegral(years).
    7. If years, months, weeks, days, hours, minutes, seconds, milliseconds, microseconds, and nanoseconds are all undefined, throw a TypeError exception.
    8. If IsValidDuration( result.[[Years]], result.[[Months]], result.[[Weeks]], result.[[Days]], result.[[Hours]], result.[[Minutes]], result.[[Seconds]], result.[[Milliseconds]], result.[[Microseconds]], result.[[Nanoseconds]]) is false, then
      1. Throw a RangeError exception.
    9. Return result.

    13.5.4 DurationSign ( duration )

    The abstract operation DurationSign takes argument duration (a Duration Record) and returns -1, 0, or 1. It returns 1 if the most significant non-zero field in the duration argument is positive, and -1 if the most significant non-zero field is negative. If all of duration's fields are zero, it returns 0. It performs the following steps when called:

    1. For each value v of « duration.[[Years]], duration.[[Months]], duration.[[Weeks]], duration.[[Days]], duration.[[Hours]], duration.[[Minutes]], duration.[[Seconds]], duration.[[Milliseconds]], duration.[[Microseconds]], duration.[[Nanoseconds]] », do
      1. If v < 0, return -1.
      2. If v > 0, return 1.
    2. Return 0.

    13.5.5 IsValidDuration ( years, months, weeks, days, hours, minutes, seconds, milliseconds, microseconds, nanoseconds )

    The abstract operation IsValidDuration takes arguments years (an integer), hours (an integer), microseconds (an integer) and returns a Boolean. It returns true if its arguments form valid input from which to construct a Duration Record, and false otherwise. It performs the following steps when called:

    1. Let sign be 0.
    2. For each value v of « years, months, weeks, days, hours, minutes, seconds, milliseconds, microseconds, nanoseconds », do
      1. If abs(months) ≥ 232, return false.
      2. If ℝ(integer. This multiplication can be implemented in C++ with an implementation of std::remquo() with sufficient bits in the quotient. String manipulation will also give an exact result, since the multiplication is by a power of 10.
      3. If abs(normalizedSeconds) ≥ 253, return false.
      4. Return true.

      13.5.6 GetDurationUnitOptions ( unit, options, baseStyle, stylesList, digitalBase, prevStyle, twoDigitHours )

      The abstract operation GetDurationUnitOptions takes arguments unit (a String), options (an Object), baseStyle (a String), stylesList (a Record. It performs the following steps when called:

      1. Let style be ? GetOption(options, unit, string, stylesList, undefined).
      2. Let displayDefault be "always".
      3. If style is undefined, then
        1. If baseStyle is "digital", then
          1. Set style to digitalBase.
          2. If unit is not one of "hours", "minutes", or "seconds", set displayDefault to "auto".
        2. Else if prevStyle is one of "fractional", "numeric" or "2-digit", then
          1. Set style to "numeric".
          2. If unit is not "minutes" or "seconds", set displayDefault to "auto".
        3. Else,
          1. Set style to baseStyle.
          2. Set displayDefault to "auto".
      4. If style is "numeric" and IsFractionalSecondUnitName(unit) is true, then
        1. Set style to "fractional".
        2. Set displayDefault to "auto".
      5. Let displayField be the string-concatenation of unit and "Display".
      6. Let display be ? GetOption(options, displayField, string, « "auto", "always" », displayDefault).
      7. Perform ? ValidateDurationUnitStyle(unit, style, display, prevStyle).
      8. If unit is "hours" and twoDigitHours is true, set style to "2-digit".
      9. If unit is "minutes" or "seconds" and prevStyle is "numeric" or "2-digit", set style to "2-digit".
      10. Return the Duration Unit Options Record { [[Style]]: style, [[Display]]: display }.

      13.5.6.1 Duration Unit Options Records

      Each Duration Unit Options Record has the fields defined in Table 23.

      Table 23: Duration Unit Options Record
      Field Name Value Type
      [[Style]] a String from the Styles column of Table 20
      [[Display]] "auto" or "always"

      13.5.6.2 ValidateDurationUnitStyle ( unit, style, display, prevStyle )

      The abstract operation ValidateDurationUnitStyle takes arguments unit (a String), style (a String), display (a String), and prevStyle (a String) and returns either a throw completion. It performs the following steps when called:

      1. If display is "always" and style is "fractional", throw a RangeError exception.
      2. If prevStyle is "fractional" and style is not "fractional", throw a RangeError exception.
      3. If prevStyle is "numeric" or "2-digit" and style is not one of "fractional", "numeric" or "2-digit", throw a RangeError exception.
      4. Return unused.
       Note
      unit is not referenced in the preceding algorithm, but it is recommended that implementations use it when constructing the message of a thrown exception.

      13.5.7 ComputeFractionalDigits ( durationFormat, duration )

      The abstract operation ComputeFractionalDigits takes arguments durationFormat (a DurationFormat Object) and duration (a Duration Record) and returns a mathematical value. It computes the sum of all values in durationFormat units with "fractional" style, expressed as a fraction of the smallest unit of durationFormat that does not use "fractional" style. It performs the following steps when called:

      1. Let result be 0.
      2. Let exponent be 3.
      3. For each row of Table 24, except the header row, in table order, do
        1. Let unitOptions be the value of durationFormat's internal slot whose name is the Internal Slot value of the current row.
        2. If unitOptions.[[Style]] is "fractional", then
          1. Let unit be the Unit value of the current row.
          2. Assert: IsFractionalSecondUnitName(unit) is true.
          3. Let value be the value of duration's field whose name is the Value Field value of the current row.
          4. Set result to result + (value / 10exponent).
          5. Set exponent to exponent + 3.
      4. Return result.

      13.5.8 NextUnitFractional ( durationFormat, unit )

      The abstract operation NextUnitFractional takes arguments durationFormat (a DurationFormat Object) and unit (a String) and returns a Boolean. It returns true if the next smallest unit uses the "fractional" style. It performs the following steps when called:

      1. If unit is "seconds" and durationFormat.[[MillisecondsOptions]].[[Style]] is "fractional", return true.
      2. If unit is "milliseconds" and durationFormat.[[MicrosecondsOptions]].[[Style]] is "fractional", return true.
      3. If unit is "microseconds" and durationFormat.[[NanosecondsOptions]].[[Style]] is "fractional", return true.
      4. Return false.

      13.5.9 FormatNumericHours ( durationFormat, hoursValue, signDisplayed )

      The abstract operation FormatNumericHours takes arguments durationFormat (a DurationFormat object), hoursValue (an integer indicating a number of hours. It creates the parts for hoursValue according to the effective locale and the formatting options of durationFormat. It performs the following steps when called:

      1. Let result be a new empty CreateDataPropertyOrThrow(nfOpts, "numberingSystem", numberingSystem).
      2. If hoursStyle is "2-digit", then
        1. Perform ! Construct(%Intl.NumberFormat%, « durationFormat.[[Locale]], nfOpts »).
        2. Let hoursParts be PartitionNumberPattern(nf, hoursValue).
        3. For each Record { [[Type]]: part.[[Type]], [[Value]]: part.[[Value]], [[Unit]]: "hour" } to result.
      3. Return result.

      13.5.10 FormatNumericMinutes ( durationFormat, minutesValue, hoursDisplayed, signDisplayed )

      The abstract operation FormatNumericMinutes takes arguments durationFormat (a DurationFormat Object), minutesValue (an integer indicating a number of minutes. It creates the parts for minutesValue according to the effective locale and the formatting options of durationFormat. It performs the following steps when called:

      1. Let result be a new empty OrdinaryObjectCreate(null).
      2. Let numberingSystem be durationFormat.[[NumberingSystem]].
      3. Perform ! CreateDataPropertyOrThrow(nfOpts, "useGrouping", false).
      4. Let nf be ! Record { [[Type]]: part.[[Type]], [[Value]]: part.[[Value]], [[Unit]]: "minute" } to result.
    3. Return result.

    13.5.11 FormatNumericSeconds ( durationFormat, secondsValue, minutesDisplayed, signDisplayed )

    The abstract operation FormatNumericSeconds takes arguments durationFormat (a DurationFormat Object), secondsValue (a mathematical value indicating a number of seconds. It creates the parts for secondsValue according to the effective locale and the formatting options of durationFormat. It performs the following steps when called:

    1. Let result be a new empty OrdinaryObjectCreate(null).
    2. Let numberingSystem be durationFormat.[[NumberingSystem]].
    3. Perform ! CreateDataPropertyOrThrow(nfOpts, "useGrouping", false).
    4. Let fractionDigits be durationFormat.[[FractionalDigits]].
    5. If fractionDigits is undefined, then
      1. Perform ! CreateDataPropertyOrThrow(nfOpts, "minimumFractionDigits", fractionDigits).
    6. Perform ! Record { [[Type]]: part.[[Type]], [[Value]]: part.[[Value]], [[Unit]]: "second" } to result.
  • Return result.
    •

    13.5.12 FormatNumericUnits ( durationFormat, duration, firstNumericUnit, signDisplayed )

    The abstract operation FormatNumericUnits takes arguments durationFormat (a DurationFormat Object), duration (a Duration Record), firstNumericUnit (a String), and signDisplayed (a Boolean) and returns a Records. It creates the parts representing the elements of duration that use "numeric" or "2-digit" style according to the effective locale and the formatting options of durationFormat. It performs the following steps when called:

    1. list-concatenation of numericPartsList and minutesParts.
    2. Set signDisplayed to false.
  • If secondsFormatted is true, then
    1. Let secondsParts be FormatNumericSeconds(durationFormat, secondsValue, minutesFormatted, signDisplayed).
    2. Set numericPartsList to the list-concatenation of numericPartsList and secondsParts.
  • Return numericPartsList.
    •

    13.5.13 IsFractionalSecondUnitName ( unit )

    The abstract operation IsFractionalSecondUnitName takes argument unit (a String) and returns a Boolean. It performs the following steps when called:

    1. If unit is one of "milliseconds", "microseconds", or "nanoseconds", return true.
    2. Return false.

    13.5.14 ListFormatParts ( durationFormat, partitionedPartsList )

    The abstract operation ListFormatParts takes arguments durationFormat (a DurationFormat Object) and partitionedPartsList (a List. It creates a Lists in partitionedPartsList according to the effective locale and the formatting options of durationFormat. It performs the following steps when called:

    1. Let lfOpts be Construct(%Intl.ListFormat%, « durationFormat.[[Locale]], lfOpts »).
    2. Let strings be a new empty List.
    3. For each Assert: listPart.[[Type]] is "literal".
    4. Append the Record { [[Type]]: "literal", [[Value]]: listPart.[[Value]], [[Unit]]: empty } to flattenedPartsList.
  • Return flattenedPartsList.
    •

    13.5.15 PartitionDurationFormatPattern ( durationFormat, duration )

    The abstract operation PartitionDurationFormatPattern takes arguments durationFormat (a DurationFormat) and duration (a Duration Record) and returns a List. It creates the corresponding parts for duration according to the effective locale and the formatting options of durationFormat. It performs the following steps when called:

    1. Let result be a new empty CreateDataPropertyOrThrow(nfOpts, "minimumFractionDigits", +0𝔽).
  • Else,
    1. Perform ! CreateDataPropertyOrThrow(nfOpts, "numberingSystem", durationFormat.[[NumberingSystem]]).
    2. If signDisplayed is true, then
      1. Set signDisplayed to false.
      2. If value is 0 and DurationSign(duration) is -1, set value to negative-zero.
    3. Else,
      1. Perform ! CreateDataPropertyOrThrow(nfOpts, "unitDisplay", style).
      2. Let nf be ! Record { [[Type]]: part.[[Type]], [[Value]]: part.[[Value]], [[Unit]]: numberFormatUnit } to list.
    4. Append list to result.
  • Return ListFormatParts(durationFormat, result).
    •
    Table 24: DurationFormat instance internal slots and properties relevant to PartitionDurationFormatPattern
    Value Field Internal Slot Unit NumberFormat Unit
    [[Years]] [[YearsOptions]] "years" "year"
    [[Months]] [[MonthsOptions]] "months" "month"
    [[Weeks]] [[WeeksOptions]] "weeks" "week"
    [[Days]] [[DaysOptions]] "days" "day"
    [[Hours]] [[HoursOptions]] "hours" "hour"
    [[Minutes]] [[MinutesOptions]] "minutes" "minute"
    [[Seconds]] [[SecondsOptions]] "seconds" "second"
    [[Milliseconds]] [[MillisecondsOptions]] "milliseconds" "millisecond"
    [[Microseconds]] [[MicrosecondsOptions]] "microseconds" "microsecond"
    [[Nanoseconds]] [[NanosecondsOptions]] "nanoseconds" "nanosecond"

    14 ListFormat Objects

    14.1 The Intl.ListFormat Constructor

    The Intl.ListFormat constructor:

    • is %Intl.ListFormat%.
    • is the initial value of the "ListFormat" property of the Intl object.

    Behaviour common to all service constructor properties of the Intl object is specified in 9.1.

    14.1.1 Intl.ListFormat ( [ locales [ , options ] ] )

    When the Intl.ListFormat function is called with optional arguments locales and options, the following steps are taken:

    1. If NewTarget is undefined, throw a TypeError exception.
    2. Let listFormat be ? OrdinaryCreateFromConstructor(NewTarget, "%Intl.ListFormat.prototype%", « [[InitializedListFormat]], [[Locale]], [[Type]], [[Style]], [[Templates]] »).
    3. Let optionsResolution be ? ResolveOptions(%Intl.ListFormat%, %Intl.ListFormat%.[[LocaleData]], locales, options).
    4. Set options to optionsResolution.[[Options]].
    5. Let r be optionsResolution.[[ResolvedLocale]].
    6. Set listFormat.[[Locale]] to r.[[Locale]].
    7. Let type be ? GetOption(options, "type", string, « "conjunction", "disjunction", "unit" », "conjunction").
    8. Set listFormat.[[Type]] to type.
    9. Let style be ? GetOption(options, "style", string, « "long", "short", "narrow" », "long").
    10. Set listFormat.[[Style]] to style.
    11. Let resolvedLocaleData be r.[[LocaleData]].
    12. Let dataLocaleTypes be resolvedLocaleData.[[<type>]].
    13. Set listFormat.[[Templates]] to dataLocaleTypes.[[<style>]].
    14. Return listFormat.

    14.2 Properties of the Intl.ListFormat Constructor

    The Intl.ListFormat constructor:

    • has a [[Prototype]] internal slot whose value is %Function.prototype%.
    • has the following properties:

    14.2.1 Intl.ListFormat.prototype

    The value of Intl.ListFormat.prototype is %Intl.ListFormat.prototype%.

    This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.

    14.2.2 Intl.ListFormat.supportedLocalesOf ( locales [ , options ] )

    When the supportedLocalesOf method is called with arguments locales and options, the following steps are taken:

    1. Let availableLocales be %Intl.ListFormat%.[[AvailableLocales]].
    2. Let requestedLocales be ? CanonicalizeLocaleList(locales).
    3. Return ? FilterLocales(availableLocales, requestedLocales, options).

    14.2.3 Internal slots

    The value of the [[AvailableLocales]] internal slot is implementation-defined within the constraints described in 9.1.

    The value of the [[RelevantExtensionKeys]] internal slot is « ».

    The value of the [[ResolutionOptionDescriptors]] internal slot is « ».

    Note 1
    Intl.ListFormat does not have any relevant extension keys.

    The value of the [[LocaleData]] internal slot is implementation-defined within the constraints described in 9.1 and the following additional constraints, for each locale value locale in %Intl.ListFormat%.[[AvailableLocales]]:

    • [[LocaleData]].[[<locale>]] is a Record which must have fields with the names of three formatting styles: [[long]], [[short]], and [[narrow]].
    • Each of those fields is considered a ListFormat template set, which must be a substring "{0}" should occur before the substring "{1}".
    Note 2
    It is recommended that implementations use the locale data provided by the Common Locale Data Repository (available at https://cldr.unicode.org/). In LDML's listPattern, conjunction corresponds to "standard", disjunction corresponds to "or", and unit corresponds to "unit".
    Note 3
    Among the list types, conjunction stands for "and"-based lists (e.g., "A, B, and C"), disjunction stands for "or"-based lists (e.g., "A, B, or C"), and unit stands for lists of values with units (e.g., "5 pounds, 12 ounces").

    14.3 Properties of the Intl.ListFormat Prototype Object

    The Intl.ListFormat prototype object:

    • is %Intl.ListFormat.prototype%.
    • is an ordinary object.
    • is not an Intl.ListFormat instance and does not have an [[InitializedListFormat]] internal slot or any of the other internal slots of Intl.ListFormat instance objects.
    • has a [[Prototype]] internal slot whose value is %Object.prototype%.

    14.3.1 Intl.ListFormat.prototype.constructor

    The initial value of Intl.ListFormat.prototype.constructor is %Intl.ListFormat%.

    14.3.2 Intl.ListFormat.prototype.resolvedOptions ( )

    This function provides access to the locale and options computed during initialization of the object.

    1. Let lf be the this value.
    2. Perform ? Assert: v is not undefined.
    3. Perform ! CreateDataPropertyOrThrow(options, p, v).
  • Return options.
    •
    Table 25: Resolved Options of ListFormat Instances
    Internal Slot Property
    [[Locale]] "locale"
    [[Type]] "type"
    [[Style]] "style"

    14.3.3 Intl.ListFormat.prototype.format ( list )

    When the format method is called with an argument list, the following steps are taken:

    1. Let lf be the this value.
    2. Perform ? RequireInternalSlot(lf, [[InitializedListFormat]]).
    3. Let stringList be ? StringListFromIterable(list).
    4. Return FormatList(lf, stringList).

    14.3.4 Intl.ListFormat.prototype.formatToParts ( list )

    When the formatToParts method is called with an argument list, the following steps are taken:

    1. Let lf be the this value.
    2. Perform ? RequireInternalSlot(lf, [[InitializedListFormat]]).
    3. Let stringList be ? StringListFromIterable(list).
    4. Return FormatListToParts(lf, stringList).

    14.3.5 Intl.ListFormat.prototype [ %Symbol.toStringTag% ]

    The initial value of the %Symbol.toStringTag% property is the String value "Intl.ListFormat".

    This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

    14.4 Properties of Intl.ListFormat Instances

    Intl.ListFormat instances inherit properties from %Intl.ListFormat.prototype%.

    Intl.ListFormat instances have an [[InitializedListFormat]] internal slot.

    Intl.ListFormat instances also have several internal slots that are computed by The Intl.ListFormat Constructor:

    • [[Locale]] is a String value with the language tag of the locale whose localization is used by the list format styles.
    • [[Type]] is one of the String values "conjunction", "disjunction", or "unit", identifying the list of types used.
    • [[Style]] is one of the String values "long", "short", or "narrow", identifying the list formatting style used.
    • [[Templates]] is a ListFormat template set.

    14.5 Abstract Operations for ListFormat Objects

    14.5.1 DeconstructPattern ( pattern, placeables )

    The abstract operation DeconstructPattern takes arguments pattern (a Pattern String) and placeables (a List.

    It deconstructs the pattern string into a List of parts.

    placeables is a List to represent the token part. Example: 

    Input:
  DeconstructPattern("AA{xx}BB{yy}CC", {
    [[xx]]: {[[Type]]: "hour", [[Value]]: "15"},
    [[yy]]: {[[Type]]: "minute", [[Value]]: "06"}
  })

Output (List of parts Records):
  «
    {[[Type]]: "literal", [[Value]]: "AA"},
    {[[Type]]: "hour", [[Value]]: "15"},
    {[[Type]]: "literal", [[Value]]: "BB"},
    {[[Type]]: "minute", [[Value]]: "06"},
    {[[Type]]: "literal", [[Value]]: "CC"}
  »

    It performs the following steps when called:

    1. Let patternParts be PartitionPattern(pattern).
    2. Let result be a new empty Assert: placeables has a field [[<part>]].
    3. Let subst be placeables.[[<part>]].
    4. If subst is a List, then
      1. For each element s of subst, do
        1. Append s to result.
    5. Else,
      1. Append subst to result.
  • Return result.
    •

    14.5.2 CreatePartsFromList ( listFormat, list )

    The abstract operation CreatePartsFromList takes arguments listFormat (an Intl.ListFormat) and list (a List of parts according to the effective locale and the formatting options of listFormat. It performs the following steps when called:

    1. Let size be the number of elements of list.
    2. If size is 0, then
      1. Return a new empty Record { [[0]]: first, [[1]]: second }.
      2. Return DeconstructPattern(pattern, placeables).
    3. Let last be the Record { [[0]]: head, [[1]]: parts }.
    4. Set parts to DeconstructPattern(pattern, placeables).
    5. Decrement i by 1.
  • Return parts.
    •  Note
    The index n to select across multiple templates permits the conjunction to be dependent on the context, as in Spanish, where either "y" or "e" may be selected, depending on the following word.

    14.5.3 FormatList ( listFormat, list )

    The abstract operation FormatList takes arguments listFormat (an Intl.ListFormat) and list (a List of Strings) and returns a String. It performs the following steps when called:

    1. Let parts be CreatePartsFromList(listFormat, list).
    2. Let result be the empty String.
    3. For each string-concatenation of result and part.[[Value]].
  • Return result.
    •

    14.5.4 FormatListToParts ( listFormat, list )

    The abstract operation FormatListToParts takes arguments listFormat (an Intl.ListFormat) and list (a List of Strings) and returns an Array. It performs the following steps when called:

    1. Let parts be CreatePartsFromList(listFormat, list).
    2. Let result be ! %Object.prototype%).
    3. Perform ! ToString(𝔽(n)), O).
    4. Increment n by 1.
  • Return result.
    •

    14.5.5 StringListFromIterable ( iterable )

    The abstract operation StringListFromIterable takes argument iterable (an throw completion. It performs the following steps when called:

    1. If iterable is undefined, then
      1. Return a new empty IteratorStepValue(iteratorRecord).
      2. If next is done, then
        1. Return list.
      3. If next IteratorClose(iteratorRecord, error).
    2. Append next to list.
     Note

    This algorithm raises exceptions when it encounters values that are not Strings, because there is no obvious locale-aware coercion for arbitrary values.

    15 Locale Objects

    15.1 The Intl.Locale Constructor

    The Intl.Locale constructor:

    • is %Intl.Locale%.
    • is the initial value of the "Locale" property of the Intl object.

    15.1.1 Intl.Locale ( tag [ , options ] )

    When the Intl.Locale function is called with an argument tag and an optional argument options, the following steps are taken:

    1. If NewTarget is undefined, throw a TypeError exception.
    2. Let localeExtensionKeys be %Intl.Locale%.[[LocaleExtensionKeys]].
    3. Let internalSlotsList be « [[InitializedLocale]], [[Locale]], [[Calendar]], [[Collation]], [[HourCycle]], [[NumberingSystem]] ».
    4. If localeExtensionKeys contains "kf", then
      1. Append [[CaseFirst]] to internalSlotsList.
    5. If localeExtensionKeys contains "kn", then
      1. Append [[Numeric]] to internalSlotsList.
    6. Let locale be ? is an Object and tag has an [[InitializedLocale]] internal slot, then
      1. Let tag be tag.[[Locale]].
    7. Else,
      1. Let tag be ? SameValue(r.[[kn]], "true") is true or r.[[kn]] is the empty String, then
        1. Set locale.[[Numeric]] to true.
      2. Else,
        1. Set locale.[[Numeric]] to false.
    8. Set locale.[[NumberingSystem]] to r.[[nu]].
    9. Return locale.

    15.1.2 UpdateLanguageId ( tag, options )

    The abstract operation UpdateLanguageId takes arguments tag (a Unicode canonicalized locale identifier) and options (an Object) and returns either a throw completion. It updates the unicode_language_id subtags in tag from the corresponding properties of options and returns the structurally valid but non-canonicalized result. It performs the following steps when called:

    1. Let baseName be GetLocaleBaseName(tag).
    2. Let language be ? GetOption(options, "language", string, empty, GetLocaleLanguage(baseName)).
    3. If language cannot be matched by the unicode_language_subtag Unicode locale nonterminal, throw a RangeError exception.
    4. Let script be ? GetOption(options, "script", string, empty, GetLocaleScript(baseName)).
    5. If script is not undefined, then
      1. If script cannot be matched by the unicode_script_subtag Unicode locale nonterminal, throw a RangeError exception.
    6. Let region be ? GetOption(options, "region", string, empty, GetLocaleRegion(baseName)).
    7. If region is not undefined, then
      1. If region cannot be matched by the unicode_region_subtag Unicode locale nonterminal, throw a RangeError exception.
    8. Let variants be ? GetOption(options, "variants", string, empty, GetLocaleVariants(baseName)).
    9. If variants is not undefined, then
      1. If variants is the empty String, throw a RangeError exception.
      2. Let lowerVariants be the ASCII-lowercase of variants.
      3. Let variantSubtags be StringSplitToList(lowerVariants, "-").
      4. For each element variant of variantSubtags, do
        1. If variant cannot be matched by the unicode_variant_subtag Unicode locale nonterminal, throw a RangeError exception.
      5. If variantSubtags contains any duplicate elements, throw a RangeError exception.
    10. Let allExtensions be the suffix of tag following baseName.
    11. Let newTag be language.
    12. If script is not undefined, set newTag to the string-concatenation of newTag and allExtensions.
    13. Return newTag.

    15.1.3 MakeLocaleRecord ( tag, options, localeExtensionKeys )

    The abstract operation MakeLocaleRecord takes arguments tag (a language tag), options (a Record in which each element of localeExtensionKeys defines a corresponding field with data from any Unicode locale extension sequence of tag as overridden by a corresponding field of options, and which additionally includes a [[locale]] field containing a Unicode canonicalized locale identifier resulting from incorporating those fields into tag. It performs the following steps when called:

    1. If tag contains a substring that is a Unicode locale extension sequence, then
      1. Let extension be the String value consisting of the substring of the Unicode locale extension sequence within tag.
      2. Let components be UnicodeExtensionComponents(extension).
      3. Let attributes be components.[[Attributes]].
      4. Let keywords be components.[[Keywords]].
    2. Else,
      1. Let attributes be a new empty Assert: options has a field [[<key>]].
      2. Let overrideValue be options.[[<key>]].
      3. If overrideValue is not undefined, then
        1. Set value to CanonicalizeUValue(key, overrideValue).
        2. If entry is not empty, then
          1. Set entry.[[Value]] to value.
        3. Else,
          1. Append the Record { [[Key]]: key, [[Value]]: value } to keywords.
      4. Set result.[[<key>]] to value.
    3. Let locale be the String value that is tag with any Unicode locale extension sequences removed.
    4. If attributes is not empty or keywords is not empty, then
      1. Set result.[[locale]] to InsertUnicodeExtensionAndCanonicalize(locale, attributes, keywords).
    5. Else,
      1. Set result.[[locale]] to CanonicalizeUnicodeLocaleId(locale).
    6. Return result.

    15.2 Properties of the Intl.Locale Constructor

    The Intl.Locale constructor:

    • has a [[Prototype]] internal slot whose value is %Function.prototype%.
    • has the following properties:

    15.2.1 Intl.Locale.prototype

    The value of Intl.Locale.prototype is %Intl.Locale.prototype%.

    This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.

    15.2.2 Internal slots

    The value of the [[LocaleExtensionKeys]] internal slot is a List that must include all elements of « "ca", "co", "hc", "nu" », must additionally include any element of « "kf", "kn" » that is also an element of %Intl.Collator%.[[RelevantExtensionKeys]], and must not include any other elements.

    15.3 Properties of the Intl.Locale Prototype Object

    The Intl.Locale prototype object:

    • is %Intl.Locale.prototype%.
    • is an ordinary object.
    • is not an Intl.Locale instance and does not have an [[InitializedLocale]] internal slot or any of the other internal slots of Intl.Locale instance objects.
    • has a [[Prototype]] internal slot whose value is %Object.prototype%.

    15.3.1 Intl.Locale.prototype.constructor

    The initial value of Intl.Locale.prototype.constructor is %Intl.Locale%.

    15.3.2 get Intl.Locale.prototype.baseName

    Intl.Locale.prototype.baseName is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

    1. Let loc be the this value.
    2. Perform ? RequireInternalSlot(loc, [[InitializedLocale]]).
    3. Return GetLocaleBaseName(loc.[[Locale]]).

    15.3.3 get Intl.Locale.prototype.calendar

    Intl.Locale.prototype.calendar is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

    1. Let loc be the this value.
    2. Perform ? RequireInternalSlot(loc, [[InitializedLocale]]).
    3. Return loc.[[Calendar]].

    15.3.4 get Intl.Locale.prototype.caseFirst

    This property only exists if %Intl.Locale%.[[LocaleExtensionKeys]] contains "kf".

    Intl.Locale.prototype.caseFirst is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

    1. Let loc be the this value.
    2. Perform ? RequireInternalSlot(loc, [[InitializedLocale]]).
    3. Return loc.[[CaseFirst]].

    15.3.5 get Intl.Locale.prototype.collation

    Intl.Locale.prototype.collation is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

    1. Let loc be the this value.
    2. Perform ? RequireInternalSlot(loc, [[InitializedLocale]]).
    3. Return loc.[[Collation]].

    15.3.6 get Intl.Locale.prototype.hourCycle

    Intl.Locale.prototype.hourCycle is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

    1. Let loc be the this value.
    2. Perform ? RequireInternalSlot(loc, [[InitializedLocale]]).
    3. Return loc.[[HourCycle]].

    15.3.7 get Intl.Locale.prototype.language

    Intl.Locale.prototype.language is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

    1. Let loc be the this value.
    2. Perform ? RequireInternalSlot(loc, [[InitializedLocale]]).
    3. Return GetLocaleLanguage(loc.[[Locale]]).

    15.3.8 Intl.Locale.prototype.maximize ( )

    1. Let loc be the this value.
    2. Perform ? Construct(%Intl.Locale%, maximal).

    15.3.9 Intl.Locale.prototype.minimize ( )

    1. Let loc be the this value.
    2. Perform ? Construct(%Intl.Locale%, minimal).

    15.3.10 get Intl.Locale.prototype.numberingSystem

    Intl.Locale.prototype.numberingSystem is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

    1. Let loc be the this value.
    2. Perform ? RequireInternalSlot(loc, [[InitializedLocale]]).
    3. Return loc.[[NumberingSystem]].

    15.3.11 get Intl.Locale.prototype.numeric

    This property only exists if %Intl.Locale%.[[LocaleExtensionKeys]] contains "kn".

    Intl.Locale.prototype.numeric is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

    1. Let loc be the this value.
    2. Perform ? RequireInternalSlot(loc, [[InitializedLocale]]).
    3. Return loc.[[Numeric]].

    15.3.12 get Intl.Locale.prototype.region

    Intl.Locale.prototype.region is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

    1. Let loc be the this value.
    2. Perform ? RequireInternalSlot(loc, [[InitializedLocale]]).
    3. Return GetLocaleRegion(loc.[[Locale]]).

    15.3.13 get Intl.Locale.prototype.script

    Intl.Locale.prototype.script is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

    1. Let loc be the this value.
    2. Perform ? RequireInternalSlot(loc, [[InitializedLocale]]).
    3. Return GetLocaleScript(loc.[[Locale]]).

    15.3.14 Intl.Locale.prototype.toString ( )

    1. Let loc be the this value.
    2. Perform ? RequireInternalSlot(loc, [[InitializedLocale]]).
    3. Return loc.[[Locale]].

    15.3.15 get Intl.Locale.prototype.variants

    Intl.Locale.prototype.variants is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

    1. Let loc be the this value.
    2. Perform ? RequireInternalSlot(loc, [[InitializedLocale]]).
    3. Return GetLocaleVariants(loc.[[Locale]]).

    15.3.16 Intl.Locale.prototype [ %Symbol.toStringTag% ]

    The initial value of the %Symbol.toStringTag% property is the String value "Intl.Locale".

    This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

    15.4 Properties of Intl.Locale Instances

    Intl.Locale instances are ordinary objects that inherit properties from %Intl.Locale.prototype%.

    Intl.Locale instances have an [[InitializedLocale]] internal slot.

    Intl.Locale instances also have several internal slots that are computed by The Intl.Locale Constructor:

    • [[Locale]] is a String value with the language tag of the locale whose localization is used for formatting.
    • [[Calendar]] is either undefined or a String value that is a well-formed Unicode Calendar Identifier in canonical form.
    • [[Collation]] is either undefined or a String value that is a well-formed Unicode Collation Identifier in canonical form.
    • [[HourCycle]] is either undefined or a String value that is a valid Unicode Hour Cycle Identifier in canonical form.
    • [[NumberingSystem]] is either undefined or a String value that is a well-formed Unicode Number System Identifier in canonical form.
    • [[CaseFirst]] is either undefined or one of the String values "upper", "lower", or "false". This internal slot only exists if the [[LocaleExtensionKeys]] internal slot of %Intl.Locale% contains "kf".
    • [[Numeric]] is either undefined or a Boolean value specifying whether numeric sorting is used by the locale. This internal slot only exists if the [[LocaleExtensionKeys]] internal slot of %Intl.Locale% contains "kn".

    15.5 Abstract Operations for Locale Objects

    15.5.1 GetLocaleBaseName ( locale )

    The abstract operation GetLocaleBaseName takes argument locale (a String) and returns a String. It performs the following steps when called:

    1. Assert: locale can be matched by the unicode_locale_id Unicode locale nonterminal.
    2. Return the longest prefix of locale matched by the unicode_language_id Unicode locale nonterminal.

    15.5.2 GetLocaleLanguage ( locale )

    The abstract operation GetLocaleLanguage takes argument locale (a String) and returns a String. It performs the following steps when called:

    1. Let baseName be GetLocaleBaseName(locale).
    2. Assert: The first subtag of baseName can be matched by the unicode_language_subtag Unicode locale nonterminal.
    3. Return the first subtag of baseName.

    15.5.3 GetLocaleScript ( locale )

    The abstract operation GetLocaleScript takes argument locale (a String) and returns a String or undefined. It performs the following steps when called:

    1. Let baseName be GetLocaleBaseName(locale).
    2. Assert: baseName contains at most one subtag that can be matched by the unicode_script_subtag Unicode locale nonterminal.
    3. If baseName contains a subtag matched by the unicode_script_subtag Unicode locale nonterminal, return that subtag.
    4. Return undefined.

    15.5.4 GetLocaleRegion ( locale )

    The abstract operation GetLocaleRegion takes argument locale (a String) and returns a String or undefined. It performs the following steps when called:

    1. Let baseName be GetLocaleBaseName(locale).
    2. NOTE: A unicode_region_subtag subtag is only valid immediately after an initial unicode_language_subtag subtag, optionally with a single unicode_script_subtag subtag between them. In that position, unicode_region_subtag cannot be confused with any other valid subtag because all their productions are disjoint.
    3. Assert: baseNameTail contains at most one subtag that can be matched by the unicode_region_subtag Unicode locale nonterminal.
    4. If baseNameTail contains a subtag matched by the unicode_region_subtag Unicode locale nonterminal, return that subtag.
    5. Return undefined.

    15.5.5 GetLocaleVariants ( locale )

    The abstract operation GetLocaleVariants takes argument locale (a String) and returns a String or undefined. It performs the following steps when called:

    1. Let baseName be GetLocaleBaseName(locale).
    2. NOTE: Each subtag in baseName that is preceded by "-" is either a unicode_script_subtag, unicode_region_subtag, or unicode_variant_subtag, but any substring matched by unicode_variant_subtag is strictly longer than any prefix thereof which could also be matched by one of the other productions.
    3. Let variants be the longest suffix of baseName that starts with a "-" followed by a substring that is matched by the unicode_variant_subtag Unicode locale nonterminal. If there is no such suffix, return undefined.
    4. Return the substring of variants from 1.

    16 NumberFormat Objects

    16.1 The Intl.NumberFormat Constructor

    The Intl.NumberFormat constructor:

    • is %Intl.NumberFormat%.
    • is the initial value of the "NumberFormat" property of the Intl object.

    Behaviour common to all service constructor properties of the Intl object is specified in 9.1.

    16.1.1 Intl.NumberFormat ( [ locales [ , options ] ] )

    When the Intl.NumberFormat function is called with optional arguments locales and options, the following steps are taken:

    1. If NewTarget is undefined, let newTarget be the constructor mode of 4.3 Note 1, then
      1. Let this be the this value.
      2. Return ? ChainNumberFormat(numberFormat, NewTarget, this).
    2. Return numberFormat.
    Normative Optional

    16.1.1.1 ChainNumberFormat ( numberFormat, newTarget, this )

    The abstract operation ChainNumberFormat takes arguments numberFormat (an Intl.NumberFormat), newTarget (an throw completion. It performs the following steps when called:

    1. If newTarget is undefined and ? DefinePropertyOrThrow(this, %Intl%.[[FallbackSymbol]], PropertyDescriptor{ [[Value]]: numberFormat, [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }).
    2. Return this.
  • Return numberFormat.
    •

    16.1.2 SetNumberFormatDigitOptions ( intlObj, options, mnfdDefault, mxfdDefault, notation )

    The abstract operation SetNumberFormatDigitOptions takes arguments intlObj (an Object), options (an Object), mnfdDefault (an throw completion. It populates the internal slots of intlObj that affect locale-independent number rounding (see 16.5.3). It performs the following steps when called:

    1. Let mnid be ? GetNumberOption(options, "minimumIntegerDigits,", 1, 21, 1).
    2. Let mnfd be ? Get(options, "maximumSignificantDigits").
    3. Set intlObj.[[MinimumIntegerDigits]] to mnid.
    4. Let roundingIncrement be ? GetNumberOption(options, "roundingIncrement", 1, 5000, 1).
    5. If roundingIncrement is not in « 1, 2, 5, 10, 20, 25, 50, 100, 200, 250, 500, 1000, 2000, 2500, 5000 », throw a RangeError exception.
    6. Let roundingMode be ? GetOption(options, "roundingMode", string, « "ceil", "floor", "expand", "trunc", "halfCeil", "halfFloor", "halfExpand", "halfTrunc", "halfEven" », "halfExpand").
    7. Let roundingPriority be ? GetOption(options, "roundingPriority", string, « "auto", "morePrecision", "lessPrecision" », "auto").
    8. Let trailingZeroDisplay be ? GetOption(options, "trailingZeroDisplay", string, « "auto", "stripIfInteger" », "auto").
    9. NOTE: All fields required by SetNumberFormatDigitOptions have now been read from options. The remainder of this AO interprets the options and may throw exceptions.
    10. If roundingIncrement is not 1, set mxfdDefault to mnfdDefault.
    11. Set intlObj.[[RoundingIncrement]] to roundingIncrement.
    12. Set intlObj.[[RoundingMode]] to roundingMode.
    13. Set intlObj.[[TrailingZeroDisplay]] to trailingZeroDisplay.
    14. If mnsd is undefined and mxsd is undefined, let hasSd be false. Otherwise, let hasSd be true.
    15. If mnfd is undefined and mxfd is undefined, let hasFd be false. Otherwise, let hasFd be true.
    16. Let needSd be true.
    17. Let needFd be true.
    18. If roundingPriority is "auto", then
      1. Set needSd to hasSd.
      2. If needSd is true, or hasFd is false and notation is "compact", then
        1. Set needFd to false.
    19. If needSd is true, then
      1. If hasSd is true, then
        1. Set intlObj.[[MinimumSignificantDigits]] to ? DefaultNumberOption(mnsd, 1, 21, 1).
        2. Set intlObj.[[MaximumSignificantDigits]] to ? DefaultNumberOption(mxsd, intlObj.[[MinimumSignificantDigits]], 21, 21).
      2. Else,
        1. Set intlObj.[[MinimumSignificantDigits]] to 1.
        2. Set intlObj.[[MaximumSignificantDigits]] to 21.
    20. If needFd is true, then
      1. If hasFd is true, then
        1. Set mnfd to ? DefaultNumberOption(mnfd, 0, 100, undefined).
        2. Set mxfd to ? DefaultNumberOption(mxfd, 0, 100, undefined).
        3. If mnfd is undefined, set mnfd to max(mxfdDefault, mnfd).
        4. Else if mnfd is greater than mxfd, throw a RangeError exception.
        5. Set intlObj.[[MinimumFractionDigits]] to mnfd.
        6. Set intlObj.[[MaximumFractionDigits]] to mxfd.
      2. Else,
        1. Set intlObj.[[MinimumFractionDigits]] to mnfdDefault.
        2. Set intlObj.[[MaximumFractionDigits]] to mxfdDefault.
    21. If needSd is false and needFd is false, then
      1. Set intlObj.[[MinimumFractionDigits]] to 0.
      2. Set intlObj.[[MaximumFractionDigits]] to 0.
      3. Set intlObj.[[MinimumSignificantDigits]] to 1.
      4. Set intlObj.[[MaximumSignificantDigits]] to 2.
      5. Set intlObj.[[RoundingType]] to more-precision.
      6. Set intlObj.[[ComputedRoundingPriority]] to "morePrecision".
    22. Else if roundingPriority is "morePrecision", then
      1. Set intlObj.[[RoundingType]] to more-precision.
      2. Set intlObj.[[ComputedRoundingPriority]] to "morePrecision".
    23. Else if roundingPriority is "lessPrecision", then
      1. Set intlObj.[[RoundingType]] to less-precision.
      2. Set intlObj.[[ComputedRoundingPriority]] to "lessPrecision".
    24. Else if hasSd is true, then
      1. Set intlObj.[[RoundingType]] to significant-digits.
      2. Set intlObj.[[ComputedRoundingPriority]] to "auto".
    25. Else,
      1. Set intlObj.[[RoundingType]] to fraction-digits.
      2. Set intlObj.[[ComputedRoundingPriority]] to "auto".
    26. If roundingIncrement is not 1, then
      1. If intlObj.[[RoundingType]] is not fraction-digits, throw a TypeError exception.
      2. If intlObj.[[MaximumFractionDigits]] is not intlObj.[[MinimumFractionDigits]], throw a RangeError exception.
    27. Return unused.

    16.1.3 SetNumberFormatUnitOptions ( intlObj, options )

    The abstract operation SetNumberFormatUnitOptions takes arguments intlObj (an Intl.NumberFormat) and options (an Object) and returns either a throw completion. It resolves the user-specified options relating to units onto intlObj. It performs the following steps when called:

    1. Let style be ? GetOption(options, "style", string, « "decimal", "percent", "currency", "unit" », "decimal").
    2. Set intlObj.[[Style]] to style.
    3. Let currency be ? GetOption(options, "currency", string, empty, undefined).
    4. If currency is undefined, then
      1. If style is "currency", throw a TypeError exception.
    5. Else,
      1. If IsWellFormedCurrencyCode(currency) is false, throw a RangeError exception.
    6. Let currencyDisplay be ? GetOption(options, "currencyDisplay", string, « "code", "symbol", "narrowSymbol", "name" », "symbol").
    7. Let currencySign be ? GetOption(options, "currencySign", string, « "standard", "accounting" », "standard").
    8. Let unit be ? GetOption(options, "unit", string, empty, undefined).
    9. If unit is undefined, then
      1. If style is "unit", throw a TypeError exception.
    10. Else,
      1. If IsWellFormedUnitIdentifier(unit) is false, throw a RangeError exception.
    11. Let unitDisplay be ? GetOption(options, "unitDisplay", string, « "short", "narrow", "long" », "short").
    12. If style is "currency", then
      1. Set intlObj.[[Currency]] to the ASCII-uppercase of currency.
      2. Set intlObj.[[CurrencyDisplay]] to currencyDisplay.
      3. Set intlObj.[[CurrencySign]] to currencySign.
    13. If style is "unit", then
      1. Set intlObj.[[Unit]] to unit.
      2. Set intlObj.[[UnitDisplay]] to unitDisplay.
    14. Return unused.

    16.2 Properties of the Intl.NumberFormat Constructor

    The Intl.NumberFormat constructor:

    • has a [[Prototype]] internal slot whose value is %Function.prototype%.
    • has the following properties:

    16.2.1 Intl.NumberFormat.prototype

    The value of Intl.NumberFormat.prototype is %Intl.NumberFormat.prototype%.

    This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.

    16.2.2 Intl.NumberFormat.supportedLocalesOf ( locales [ , options ] )

    When the supportedLocalesOf method is called with arguments locales and options, the following steps are taken:

    1. Let availableLocales be %Intl.NumberFormat%.[[AvailableLocales]].
    2. Let requestedLocales be ? CanonicalizeLocaleList(locales).
    3. Return ? FilterLocales(availableLocales, requestedLocales, options).

    16.2.3 Internal slots

    The value of the [[AvailableLocales]] internal slot is implementation-defined within the constraints described in 9.1.

    The value of the [[RelevantExtensionKeys]] internal slot is « "nu" ».

    The value of the [[ResolutionOptionDescriptors]] internal slot is « { [[Key]]: "nu", [[Property]]: "numberingSystem" } ».

    Note 1
    Unicode Technical Standard #35 Part 1 Core, Section 3.6.1 Key and Type Definitions describes three locale extension keys that are relevant to number formatting: "cu" for currency, "cf" for currency format style, and "nu" for numbering system. Intl.NumberFormat, however, requires that the currency of a currency format is specified through the currency property in the options objects, and the currency format style of a currency format is specified through the currencySign property in the options objects.

    The value of the [[LocaleData]] internal slot is implementation-defined within the constraints described in 9.1 and the following additional constraints:

    • The List that is the value of the "nu" field of any locale field of [[LocaleData]] must not include the values "native", "traditio", or "finance".
    • [[LocaleData]].[[<locale>]] must have a [[patterns]] field for all locale values locale. The value of this field must be a Record, which must have fields with the names of the four number format styles: "decimal", "percent", "currency", and "unit".
    • The two fields "currency" and "unit" noted above must be Records with at least one field, "fallback". The "currency" may have additional fields with keys corresponding to currency codes according to 6.3. Each field of "currency" must be a Record with fields corresponding to the possible currencyDisplay values: "code", "symbol", "narrowSymbol", and "name". Each of those fields must contain a Record with fields corresponding to the possible currencySign values: "standard" or "accounting". The "unit" field (of [[LocaleData]].[[<locale>]]) may have additional fields beyond the required field "fallback" with keys corresponding to core measurement unit identifiers corresponding to 6.6. Each field of "unit" must be a Record with fields corresponding to the possible unitDisplay values: "narrow", "short", and "long".
    • All of the leaf fields so far described for the patterns tree ("decimal", "percent", great-grandchildren of "currency", and grandchildren of "unit") must be Records with the keys "positivePattern", "zeroPattern", and "negativePattern".
    • The value of the aforementioned fields (the sign-dependent pattern fields) must be string values that must contain the substring "{number}". "positivePattern" must contain the substring "{minusSign}" but not "{plusSign}"; and "zeroPattern" must not contain either "{plusSign}" or "{minusSign}". Additionally, the values within the "percent" field must also contain the substring "{percentSign}"; the values within the "currency" field must also contain one or more of the following substrings: "{currencyCode}", "{currencyPrefix}", or "{currencySuffix}"; and the values within the "unit" field must also contain one or more of the following substrings: "{unitPrefix}" or "{unitSuffix}". The pattern strings, when interpreted as a sequence of UTF-16 encoded code points as described in ECMA-262, 6.1.4, must not contain any code points in the General Category "Number, decimal digit" as specified by the Unicode Standard.
    • [[LocaleData]].[[<locale>]] must also have a [[notationSubPatterns]] field for all locale values locale. The value of this field must be a integer keys corresponding to all discrete magnitudes the implementation supports for compact notation. Each of these fields must be a string value which may contain the substring "{compactName}".
    Note 2
    It is recommended that implementations use the locale data provided by the Common Locale Data Repository (available at https://cldr.unicode.org/).

    16.3 Properties of the Intl.NumberFormat Prototype Object

    The Intl.NumberFormat prototype object:

    • is %Intl.NumberFormat.prototype%.
    • is an ordinary object.
    • is not an Intl.NumberFormat instance and does not have an [[InitializedNumberFormat]] internal slot or any of the other internal slots of Intl.NumberFormat instance objects.
    • has a [[Prototype]] internal slot whose value is %Object.prototype%.

    16.3.1 Intl.NumberFormat.prototype.constructor

    The initial value of Intl.NumberFormat.prototype.constructor is %Intl.NumberFormat%.

    16.3.2 Intl.NumberFormat.prototype.resolvedOptions ( )

    This function provides access to the locale and options computed during initialization of the object.

    1. Let nf be the this value.
    2. If the implementation supports the normative optional %Object.prototype%).
    3. For each row of Table 26, except the header row, in table order, do
      1. Let p be the Property value of the current row.
      2. Let v be the value of nf's internal slot whose name is the Internal Slot value of the current row.
      3. If v is not undefined, then
        1. If there is a Conversion value in the current row, then
          1. CreateDataPropertyOrThrow(options, p, v).
      4. Return options.
      Table 26: Resolved Options of NumberFormat Instances
      Internal Slot Property Conversion
      [[Locale]] "locale"
      [[NumberingSystem]] "numberingSystem"
      [[Style]] "style"
      [[Currency]] "currency"
      [[CurrencyDisplay]] "currencyDisplay"
      [[CurrencySign]] "currencySign"
      [[Unit]] "unit"
      [[UnitDisplay]] "unitDisplay"
      [[MinimumIntegerDigits]] "minimumIntegerDigits" number
      [[MinimumFractionDigits]] "minimumFractionDigits" number
      [[MaximumFractionDigits]] "maximumFractionDigits" number
      [[MinimumSignificantDigits]] "minimumSignificantDigits" number
      [[MaximumSignificantDigits]] "maximumSignificantDigits" number
      [[UseGrouping]] "useGrouping"
      [[Notation]] "notation"
      [[CompactDisplay]] "compactDisplay"
      [[SignDisplay]] "signDisplay"
      [[RoundingIncrement]] "roundingIncrement" number
      [[RoundingMode]] "roundingMode"
      [[ComputedRoundingPriority]] "roundingPriority"
      [[TrailingZeroDisplay]] "trailingZeroDisplay"

      16.3.3 get Intl.NumberFormat.prototype.format

      Intl.NumberFormat.prototype.format is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

      1. Let nf be the this value.
      2. If the implementation supports the normative optional function object as defined in Number Format Functions (16.5.2).
      3. Set F.[[NumberFormat]] to nf.
      4. Set nf.[[BoundFormat]] to F.
    4. Return nf.[[BoundFormat]].
     Note
    The returned function is bound to nf so that it can be passed directly to Array.prototype.map or other functions. This is considered a historical artefact, as part of a convention which is no longer followed for new features, but is preserved to maintain compatibility with existing programs.

    16.3.4 Intl.NumberFormat.prototype.formatRange ( start, end )

    When the formatRange method is called with arguments start and end, the following steps are taken:

    1. Let nf be the this value.
    2. Perform ? RequireInternalSlot(nf, [[InitializedNumberFormat]]).
    3. If start is undefined or end is undefined, throw a TypeError exception.
    4. Let x be ? ToIntlMathematicalValue(start).
    5. Let y be ? ToIntlMathematicalValue(end).
    6. Return ? FormatNumericRange(nf, x, y).

    16.3.5 Intl.NumberFormat.prototype.formatRangeToParts ( start, end )

    When the formatRangeToParts method is called with arguments start and end, the following steps are taken:

    1. Let nf be the this value.
    2. Perform ? RequireInternalSlot(nf, [[InitializedNumberFormat]]).
    3. If start is undefined or end is undefined, throw a TypeError exception.
    4. Let x be ? ToIntlMathematicalValue(start).
    5. Let y be ? ToIntlMathematicalValue(end).
    6. Return ? FormatNumericRangeToParts(nf, x, y).

    16.3.6 Intl.NumberFormat.prototype.formatToParts ( value )

    When the formatToParts method is called with an optional argument value, the following steps are taken:

    1. Let nf be the this value.
    2. Perform ? RequireInternalSlot(nf, [[InitializedNumberFormat]]).
    3. Let x be ? ToIntlMathematicalValue(value).
    4. Return FormatNumericToParts(nf, x).

    16.3.7 Intl.NumberFormat.prototype [ %Symbol.toStringTag% ]

    The initial value of the %Symbol.toStringTag% property is the String value "Intl.NumberFormat".

    This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

    16.4 Properties of Intl.NumberFormat Instances

    Intl.NumberFormat instances are ordinary objects that inherit properties from %Intl.NumberFormat.prototype%.

    Intl.NumberFormat instances have an [[InitializedNumberFormat]] internal slot.

    Intl.NumberFormat instances also have several internal slots that are computed by The Intl.NumberFormat Constructor:

    • [[Locale]] is a String value with the language tag of the locale whose localization is used for formatting.
    • [[LocaleData]] is a Record representing the data available to the implementation for formatting. It is the value of an entry in %Intl.NumberFormat%.[[LocaleData]] associated with either the value of [[Locale]] or a prefix thereof.
    • [[NumberingSystem]] Unicode Number System Identifier used for formatting.
    • [[Style]] is one of the String values "decimal", "currency", "percent", or "unit", identifying the type of quantity being measured.
    • [[Currency]] is a String value with the currency code identifying the currency to be used if formatting with the "currency" unit type. It is only used when [[Style]] has the value "currency".
    • [[CurrencyDisplay]] is one of the String values "code", "symbol", "narrowSymbol", or "name", specifying whether to display the currency as an ISO 4217 alphabetic currency code, a localized currency symbol, or a localized currency name if formatting with the "currency" style. It is only used when [[Style]] has the value "currency".
    • [[CurrencySign]] is one of the String values "standard" or "accounting", specifying whether to render negative numbers in accounting format, often signified by parenthesis. It is only used when [[Style]] has the value "currency" and when [[SignDisplay]] is not "never".
    • [[Unit]] is a core unit identifier. It is only used when [[Style]] has the value "unit".
    • [[UnitDisplay]] is one of the String values "short", "narrow", or "long", specifying whether to display the unit as a symbol, narrow symbol, or localized long name if formatting with the "unit" style. It is only used when [[Style]] has the value "unit".
    • [[MinimumIntegerDigits]] is a non-negative integer digits to be used. Numbers will be padded with leading zeroes if necessary.
    • [[MinimumFractionDigits]] and [[MaximumFractionDigits]] are non-negative integers indicating the minimum and maximum fraction digits to be used. Numbers will be rounded or padded with trailing zeroes if necessary. These properties are only used when [[RoundingType]] is fraction-digits, more-precision, or less-precision.
    • [[MinimumSignificantDigits]] and [[MaximumSignificantDigits]] are positive integers indicating the minimum and maximum fraction digits to be shown. If present, the formatter uses however many fraction digits are required to display the specified number of significant digits. These properties are only used when [[RoundingType]] is significant-digits, more-precision, or less-precision.
    • [[UseGrouping]] implementation-defined. A value "always" hints the implementation to display grouping separators if possible; "min2", if there are at least 2 digits in a group; "auto", if the locale prefers to use grouping separators for the formatted number. A value false disables grouping separators.
    • [[RoundingType]] is one of the values fraction-digits, significant-digits, more-precision, or less-precision, indicating which rounding strategy to use. If fraction-digits, formatted numbers are rounded according to [[MinimumFractionDigits]] and [[MaximumFractionDigits]], as described above. If significant-digits, formatted numbers are rounded according to [[MinimumSignificantDigits]] and [[MaximumSignificantDigits]] as described above. If more-precision or less-precision, all four of those settings are used, with specific rules for disambiguating when to use one set versus the other. [[RoundingType]] is derived from the "roundingPriority" option.
    • [[ComputedRoundingPriority]] is one of the String values "auto", "morePrecision", or "lessPrecision". It is only used in 16.3.2 to convert [[RoundingType]] back to a valid "roundingPriority" option.
    • [[Notation]] is one of the String values "standard", "scientific", "engineering", or "compact", specifying whether the formatted number should be displayed without scaling, scaled to the units place with the power of ten in scientific notation, scaled to the nearest thousand with the power of ten in scientific notation, or scaled to the nearest ILD compact decimal notation power of ten with the corresponding compact decimal notation affix.
    • [[CompactDisplay]] is one of the String values "short" or "long", specifying whether to display compact notation affixes in short form ("5K") or long form ("5 thousand") if formatting with the "compact" notation. It is only used when [[Notation]] has the value "compact".
    • [[SignDisplay]] is one of the String values "auto", "always", "never", "exceptZero", or "negative", specifying when to include a sign (with non-"auto" options respectively corresponding with inclusion always, never, only for non-zero numbers, or only for non-zero negative numbers). In scientific notation, this slot affects the sign display of the mantissa but not the exponent.
    • [[RoundingIncrement]] is an integer that evenly divides 10, 100, 1000, or 10000 into tenths, fifths, quarters, or halves. It indicates the increment at which rounding should take place relative to the calculated rounding magnitude. For example, if [[MaximumFractionDigits]] is 2 and [[RoundingIncrement]] is 5, then formatted numbers are rounded to the nearest 0.05 ("nickel rounding").
    • [[RoundingMode]] is a rounding mode, one of the String values in the Identifier column of Table 27.
    • [[TrailingZeroDisplay]] is one of the String values "auto" or "stripIfInteger", indicating whether to strip trailing zeros if the formatted number is an integer (i.e., has no non-zero fraction digit).
    Table 27: Rounding modes in Intl.NumberFormat
    Identifier Description Examples: Round to 0 fraction digits
    -1.5 0.4 0.5 0.6 1.5
    "ceil" Toward positive infinity ⬆️ [-1] ⬆️ [1] ⬆️ [2]
    "floor" Toward negative infinity ⬇️ [-2] ⬇️ [0] ⬇️ [1]
    "expand" Away from zero ⬇️ [-2] ⬆️ [1] ⬆️ [2]
    "trunc" Toward zero ⬆️ [-1] ⬇️ [0] ⬇️ [1]
    "halfCeil" Ties toward positive infinity ⬆️ [-1] ⬇️ [0] ⬆️ [1] ⬆️ [2]
    "halfFloor" Ties toward negative infinity ⬇️ [-2] ⬇️ [0] ⬆️ [1] ⬇️ [1]
    "halfExpand" Ties away from zero ⬇️ [-2] ⬇️ [0] ⬆️ [1] ⬆️ [2]
    "halfTrunc" Ties toward zero ⬆️ [-1] ⬇️ [0] ⬆️ [1] ⬇️ [1]
    "halfEven" Ties toward an even rounding increment multiple ⬇️ [-2] ⬇️ [0] ⬆️ [1] ⬆️ [2]
    Note
    The examples are illustrative of the unique behaviour of each option. ⬆️ means "resolves toward positive infinity"; ⬇️ means "resolves toward negative infinity".

    Finally, Intl.NumberFormat instances have a [[BoundFormat]] internal slot that caches the function returned by the format accessor (16.3.3).

    16.5 Abstract Operations for NumberFormat Objects

    16.5.1 CurrencyDigits ( currency )

    The integer. It performs the following steps when called:

    1. integer indicating the number of fractional digits used when formatting quantities of the currency corresponding to currency. If there is no available information on the number of digits to be used, return 2.

    16.5.2 Number Format Functions

    A Number format function is an anonymous built-in function that has a [[NumberFormat]] internal slot.

    When a Number format function F is called with optional argument value, the following steps are taken:

    1. Let nf be F.[[NumberFormat]].
    2. is an Object and nf has an [[InitializedNumberFormat]] internal slot.
    3. If value is not provided, let value be undefined.
    4. Let x be ? ToIntlMathematicalValue(value).
    5. Return FormatNumeric(nf, x).

    The "length" property of a Number format function is 1𝔽.

    16.5.3 FormatNumericToString ( intlObject, x )

    The abstract operation FormatNumericToString takes arguments intlObject (an Object) and x (a mathematical value or negative-zero) and [[FormattedString]] (a String). It rounds x to an Intl mathematical value according to the internal slots of intlObject. The [[RoundedNumber]] field contains the rounded result value and the [[FormattedString]] field contains a String value representation of that result formatted according to the internal slots of intlObject. It performs the following steps when called:

    1. modulo 1 = 0, then
      1. Let i be Record { [[RoundedNumber]]: x, [[FormattedString]]: string }.

      16.5.4 PartitionNumberPattern ( numberFormat, x )

      The abstract operation PartitionNumberPattern takes arguments numberFormat (an object initialized as a NumberFormat) and x (an Intl mathematical value) and returns a mathematical value of x according to the effective locale and the formatting options of numberFormat. It performs the following steps when called:

      1. Let exponent be 0.
      2. If x is not-a-number, then
        1. Let n be an ILD String value indicating the NaN value.
      3. Else if x is positive-infinity, then
        1. Let n be an ILD String value indicating positive infinity.
      4. Else if x is negative-infinity, then
        1. Let n be an ILD String value indicating negative infinity.
      5. Else,
        1. If x is not negative-zero, then
          1. Record { [[Type]], [[Value]] } patternPart of patternParts, do
            1. Let p be patternPart.[[Type]].
            2. If p is "literal", then
              1. Append the Record { [[Type]]: "minusSign", [[Value]]: minusSignSymbol } to result.
            3. Else if p is "percentSign" and numberFormat.[[Style]] is "percent", then
              1. Let percentSignSymbol be the ILND String representing the percent sign.
              2. Append the Record { [[Type]]: "currency", [[Value]]: cd } to result.
            4. Else if p is "currencyPrefix" and numberFormat.[[Style]] is "currency", then
              1. Let currency be numberFormat.[[Currency]].
              2. Let currencyDisplay be numberFormat.[[CurrencyDisplay]].
              3. Let cd be an ILD String value representing currency before x in currencyDisplay form, which may depend on x in languages having different plural forms.
              4. Append the Record { [[Type]]: "unknown", [[Value]]: unknown } to result.
          2. Return result.

          16.5.5 PartitionNotationSubPattern ( numberFormat, x, n, exponent )

          The abstract operation PartitionNotationSubPattern takes arguments numberFormat (an Intl.NumberFormat), x (an Intl mathematical value), n (a String), and exponent (an Records with fields [[Type]] (a String) and [[Value]] (a String). x is an Intl mathematical value after rounding is applied and n is an intermediate formatted string. It creates the corresponding parts for the number and notation according to the effective locale and the formatting options of numberFormat. It performs the following steps when called:

          1. Let result be a new empty Record { [[Type]], [[Value]] } patternPart of patternParts, do
            1. Let p be patternPart.[[Type]].
            2. If p is "literal", then
              1. Append the CodePointsToString(« digits[i] »).
            3. Set transliterated to the substring of n from decimalSepIndex + 1.
          2. Else,
            1. Let integer be n.
            2. Let fraction be undefined.
          3. If the numberFormat.[[UseGrouping]] is false, then
            1. Append the List is greater than 0.
            2. Repeat, while groups Record { [[Type]]: "group", [[Value]]: groupSepSymbol } to result.
      6. If fraction is not undefined, then
        1. Let decimalSepSymbol be the ILND String representing the decimal separator.
        2. Append the Record { [[Type]]: "compact", [[Value]]: compactName } to result.
      7. Else if p is "scientificSeparator", then
        1. Let scientificSeparator be the ILND String representing the exponent separator.
        2. Append the Record { [[Type]]: "unknown", [[Value]]: unknown } to result.
  • Return result.
    •
    Table 28: Numbering systems with simple digit mappings
    Numbering System Digits
    adlm U+1E950 to U+1E959
    ahom U+11730 to U+11739
    arab U+0660 to U+0669
    arabext U+06F0 to U+06F9
    bali U+1B50 to U+1B59
    beng U+09E6 to U+09EF
    bhks U+11C50 to U+11C59
    brah U+11066 to U+1106F
    cakm U+11136 to U+1113F
    cham U+AA50 to U+AA59
    deva U+0966 to U+096F
    diak U+11950 to U+11959
    fullwide U+FF10 to U+FF19
    gara U+10D40 to U+10D49
    gong U+11DA0 to U+11DA9
    gonm U+11D50 to U+11D59
    gujr U+0AE6 to U+0AEF
    gukh U+16130 to U+16139
    guru U+0A66 to U+0A6F
    hanidec U+3007, U+4E00, U+4E8C, U+4E09, U+56DB, U+4E94, U+516D, U+4E03, U+516B, U+4E5D
    hmng U+16B50 to U+16B59
    hmnp U+1E140 to U+1E149
    java U+A9D0 to U+A9D9
    kali U+A900 to U+A909
    kawi U+11F50 to U+11F59
    khmr U+17E0 to U+17E9
    knda U+0CE6 to U+0CEF
    krai U+16D70 to U+16D79
    lana U+1A80 to U+1A89
    lanatham U+1A90 to U+1A99
    laoo U+0ED0 to U+0ED9
    latn U+0030 to U+0039
    lepc U+1C40 to U+1C49
    limb U+1946 to U+194F
    mathbold U+1D7CE to U+1D7D7
    mathdbl U+1D7D8 to U+1D7E1
    mathmono U+1D7F6 to U+1D7FF
    mathsanb U+1D7EC to U+1D7F5
    mathsans U+1D7E2 to U+1D7EB
    mlym U+0D66 to U+0D6F
    modi U+11650 to U+11659
    mong U+1810 to U+1819
    mroo U+16A60 to U+16A69
    mtei U+ABF0 to U+ABF9
    mymr U+1040 to U+1049
    mymrepka U+116DA to U+116E3
    mymrpao U+116D0 to U+116D9
    mymrshan U+1090 to U+1099
    mymrtlng U+A9F0 to U+A9F9
    nagm U+1E4F0 to U+1E4F9
    newa U+11450 to U+11459
    nkoo U+07C0 to U+07C9
    olck U+1C50 to U+1C59
    onao U+1E5F1 to U+1E5FA
    orya U+0B66 to U+0B6F
    osma U+104A0 to U+104A9
    outlined U+1CCF0 to U+1CCF9
    rohg U+10D30 to U+10D39
    saur U+A8D0 to U+A8D9
    segment U+1FBF0 to U+1FBF9
    shrd U+111D0 to U+111D9
    sind U+112F0 to U+112F9
    sinh U+0DE6 to U+0DEF
    sora U+110F0 to U+110F9
    sund U+1BB0 to U+1BB9
    sunu U+11BF0 to U+11BF9
    takr U+116C0 to U+116C9
    talu U+19D0 to U+19D9
    tamldec U+0BE6 to U+0BEF
    telu U+0C66 to U+0C6F
    thai U+0E50 to U+0E59
    tibt U+0F20 to U+0F29
    tirh U+114D0 to U+114D9
    tnsa U+16AC0 to U+16AC9
    vaii U+A620 to U+A629
    wara U+118E0 to U+118E9
    wcho U+1E2F0 to U+1E2F9
    Note 1
    The computations rely on ILD and ILND String values and locations within numeric strings that depend on the effective locale of numberFormat, or upon the effective locale and numbering system of numberFormat. The ILD and ILND String values mentioned, other than those for currency names, must not contain any code points in the General Category "Number, decimal digit" as specified by the Unicode Standard.
    Note 2
    It is recommended that implementations use the locale provided by the Common Locale Data Repository (available at https://cldr.unicode.org/).

    16.5.6 FormatNumeric ( numberFormat, x )

    The abstract operation FormatNumeric takes arguments numberFormat (an Intl.NumberFormat) and x (an Intl mathematical value) and returns a String. It performs the following steps when called:

    1. Let parts be PartitionNumberPattern(numberFormat, x).
    2. Let result be the empty String.
    3. For each string-concatenation of result and part.[[Value]].
  • Return result.
    •

    16.5.7 FormatNumericToParts ( numberFormat, x )

    The abstract operation FormatNumericToParts takes arguments numberFormat (an Intl.NumberFormat) and x (an Intl mathematical value) and returns an Array. It performs the following steps when called:

    1. Let parts be PartitionNumberPattern(numberFormat, x).
    2. Let result be ! %Object.prototype%).
    3. Perform ! ToString(𝔽(n)), O).
    4. Increment n by 1.
  • Return result.
    •

    16.5.8 ToRawPrecision ( x, minPrecision, maxPrecision, unsignedRoundingMode )

    The abstract operation ToRawPrecision takes arguments x (a non-negative integer in the integer), and [[RoundingMagnitude]] (an integer).

    It involves solving the following equation, which returns a valid integer inputs:

    ToRawPrecisionFn(n, e, p) = n × 10e–p+1
    where 10p–1 ≤ n < 10p

    It performs the following steps when called:

    1. Let p be maxPrecision.
    2. If x = 0, then
      1. Let m be the String consisting of p occurrences of the code unit 0x0030 (DIGIT ZERO).
      2. Let e be 0.
      3. Let xFinal be 0.
    3. Else,
      1. Let n1 and e1 each be an mathematical value, with r2 = ToRawPrecisionFn(n2, e2, p), such that r2 ≥ x and r2 is minimized.
      2. Let xFinal be ApplyUnsignedRoundingMode(x, r1, r2, unsignedRoundingMode).
      3. If xFinal is r1, then
        1. Let n be n1.
        2. Let e be e1.
      4. Else,
        1. Let n be n2.
        2. Let e be e2.
      5. Let m be the String consisting of the digits of the decimal representation of n (in order, with no leading zeroes).
    4. If e ≥ (p - 1), then
      1. Set m to the string-concatenation of "0.", -(e + 1) occurrences of the code unit 0x0030 (DIGIT ZERO), and m.
      2. Let int be 1.
    5. If m contains the code unit 0x002E (FULL STOP) and maxPrecision > minPrecision, then
      1. Let cut be maxPrecision - minPrecision.
      2. Repeat, while cut > 0 and the last code unit of m is 0x0030 (DIGIT ZERO),
        1. Remove the last code unit from m.
        2. Set cut to cut - 1.
      3. If the last code unit of m is 0x002E (FULL STOP), then
        1. Remove the last code unit from m.
    6. Return the Record { [[FormattedString]]: m, [[RoundedNumber]]: xFinal, [[IntegerDigitsCount]]: int, [[RoundingMagnitude]]: e–p+1 }.

    16.5.9 ToRawFixed ( x, minFraction, maxFraction, roundingIncrement, unsignedRoundingMode )

    The abstract operation ToRawFixed takes arguments x (a non-negative integer in the mathematical value), [[IntegerDigitsCount]] (an integer).

    It involves solving the following equation, which returns a valid integer inputs:

    ToRawFixedFn(n, f) = n × 10–f

    It performs the following steps when called:

    1. Let f be maxFraction.
    2. Let n1 be an integer and r2 a string-concatenation of a, ".", and b.
    3. Let int be the length of a.
  • Else,
    1. Let int be the length of m.
  • Let cut be maxFraction - minFraction.
  • Repeat, while cut > 0 and the last code unit of m is 0x0030 (DIGIT ZERO),
    1. Remove the last code unit from m.
    2. Set cut to cut - 1.
  • If the last code unit of m is 0x002E (FULL STOP), then
    1. Remove the last code unit from m.
  • Return the Record { [[FormattedString]]: m, [[RoundedNumber]]: xFinal, [[IntegerDigitsCount]]: int, [[RoundingMagnitude]]: –f }.
    •
    Normative Optional

    16.5.10 UnwrapNumberFormat ( nf )

    The abstract operation UnwrapNumberFormat takes argument nf (an throw completion. It returns the NumberFormat instance of its input object, which is either the value itself or a value associated with it by %Intl.NumberFormat% according to the normative optional constructor mode of 4.3 Note 1. It performs the following steps when called:

    1. If nf Get(nf, %Intl%.[[FallbackSymbol]]).
  • Return nf.
    •

    16.5.11 GetNumberFormatPattern ( numberFormat, x )

    The abstract operation GetNumberFormatPattern takes arguments numberFormat (an Intl.NumberFormat) and x (an Intl mathematical value) and returns a String. It considers the resolved unit-related options in the number format object along with the final scaled and rounded number being formatted (an Intl mathematical value) and returns a pattern, a String value as described in 16.2.3. It performs the following steps when called:

    1. Let resolvedLocaleData be numberFormat.[[LocaleData]].
    2. Let patterns be resolvedLocaleData.[[patterns]].
    3. Assert: x is a Assert: signDisplay is "negative".
    4. If category is negative-non-zero, then
      1. Let pattern be patterns.[[negativePattern]].
    5. Else,
      1. Let pattern be patterns.[[zeroPattern]].
  • Return pattern.
    •

    16.5.12 GetNotationSubPattern ( numberFormat, exponent )

    The abstract operation GetNotationSubPattern takes arguments numberFormat (an Intl.NumberFormat) and exponent (an integer) and returns a String. It considers the resolved notation and exponent, and returns a String value for the notation sub pattern as described in 16.2.3. It performs the following steps when called:

    1. Let resolvedLocaleData be numberFormat.[[LocaleData]].
    2. Let notationSubPatterns be resolvedLocaleData.[[notationSubPatterns]].
    3. Assert: notation is "compact".
    4. Let compactDisplay be numberFormat.[[CompactDisplay]].
    5. Let compactPatterns be notationSubPatterns.[[compact]].[[<compactDisplay>]].
    6. Return compactPatterns.[[<exponent>]].
  • Else,
    1. Return "{number}".
    •

    16.5.13 ComputeExponent ( numberFormat, x )

    The abstract operation ComputeExponent takes arguments numberFormat (an Intl.NumberFormat) and x (a integer. It computes an exponent (power of ten) by which to scale x according to the number formatting settings. It handles cases such as 999 rounding up to 1000, requiring a different exponent. It performs the following steps when called:

    1. If x = 0, then
      1. Return 0.
    2. If x < 0, then
      1. Let x = -x.
    3. Let magnitude be the base 10 logarithm of x rounded down to the nearest integer.
    4. If newMagnitude is magnitude - exponent, then
      1. Return exponent.
    5. Return ComputeExponentForMagnitude(numberFormat, magnitude + 1).

    16.5.14 ComputeExponentForMagnitude ( numberFormat, magnitude )

    The abstract operation ComputeExponentForMagnitude takes arguments numberFormat (an Intl.NumberFormat) and magnitude (an integer. It computes an exponent by which to scale a number of the given magnitude (power of ten of the most significant digit) according to the locale and the desired notation (scientific, engineering, or compact). It performs the following steps when called:

    1. Let notation be numberFormat.[[Notation]].
    2. If notation is "standard", then
      1. Return 0.
    3. Else if notation is "scientific", then
      1. Return magnitude.
    4. Else if notation is "engineering", then
      1. Let thousands be the greatest integer by which to scale a number of the given magnitude in compact notation for the current locale.
      2. Return exponent.

    16.5.15 Runtime Semantics: StringIntlMV

    The syntax-directed operation StringIntlMV takes no arguments.

    Note

    The conversion of a 12.9.3), but some of the details are different.

    It is defined piecewise over the following productions:

    StrWhiteSpaceopt
    1. Return 0.
     StringNumericLiteral ::: StrWhiteSpaceopt StrNumericLiteral StrWhiteSpaceopt
    1. Return StringIntlMV of StrNumericLiteral.
     NonDecimalIntegerLiteral
    1. Return MV of NonDecimalIntegerLiteral.
     StrDecimalLiteral ::: - StrUnsignedDecimalLiteral
    1. Let a be StringIntlMV of StrUnsignedDecimalLiteral.
    2. If a is 0, return negative-zero.
    3. If a is positive-infinity, return negative-infinity.
    4. Return -a.
     StrUnsignedDecimalLiteral ::: Infinity
    1. Return positive-infinity.
     StrUnsignedDecimalLiteral ::: DecimalDigits . DecimalDigitsopt ExponentPartopt
    1. Let a be MV of the first DecimalDigits.
  • Else,
    1. Let b be 0.
    2. Let n be 0.
  • If ExponentPart. Otherwise, let e be 0.
  • Return (a + (b × 10-n)) × 10e.
    •  StrUnsignedDecimalLiteral ::: . DecimalDigits ExponentPartopt
    1. Let b be MV of DecimalDigits.
    2. Return b × 10e - n.
     StrUnsignedDecimalLiteral ::: DecimalDigits ExponentPartopt
    1. Let a be MV of ExponentPart. Otherwise, let e be 0.
    2. Return a × 10e.

    16.5.16 ToIntlMathematicalValue ( value )

    The abstract operation ToIntlMathematicalValue takes argument value (an throw completion. It returns value converted to an Intl mathematical value, which is a mathematical value together with positive-infinity, negative-infinity, not-a-number, and negative-zero. This abstract operation is similar to mathematical value can be returned instead of a Number or BigInt, so that exact decimal values can be represented. It performs the following steps when called:

    1. Let primValue be ? is a String, then
      1. Let str be primValue.
    2. Else,
      1. Let x be ? ParseText(text, RoundMVResult(abs(intlMV)).
      2. If rounded is +∞𝔽 and intlMV < 0, return negative-infinity.
      3. If rounded is +∞𝔽, return positive-infinity.
      4. If rounded is +0𝔽 and intlMV < 0, return negative-zero.
      5. If rounded is +0𝔽, return 0.
    3. Return intlMV.

    16.5.17 GetUnsignedRoundingMode ( roundingMode, sign )

    The abstract operation GetUnsignedRoundingMode takes arguments roundingMode (a rounding mode) and sign (negative or positive) and returns a specification type from the Unsigned Rounding Mode column of Table 29. It returns the rounding mode that should be applied to the absolute value of a number to produce the same result as if roundingMode were applied to the signed value of the number (negative if sign is negative, or positive otherwise). It performs the following steps when called:

    1. Return the specification type in the Unsigned Rounding Mode column of Table 29 for the row where the value in the Identifier column is roundingMode and the value in the Sign column is sign.
    Table 29: Conversion from rounding mode to unsigned rounding mode
    Identifier Sign Unsigned Rounding Mode
    "ceil" positive infinity
    negative zero
    "floor" positive zero
    negative infinity
    "expand" positive infinity
    negative infinity
    "trunc" positive zero
    negative zero
    "halfCeil" positive half-infinity
    negative half-zero
    "halfFloor" positive half-zero
    negative half-infinity
    "halfExpand" positive half-infinity
    negative half-infinity
    "halfTrunc" positive half-zero
    negative half-zero
    "halfEven" positive half-even
    negative half-even

    16.5.18 ApplyUnsignedRoundingMode ( x, r1, r2, unsignedRoundingMode )

    The abstract operation ApplyUnsignedRoundingMode takes arguments x (a mathematical value. It considers x, bracketed below by r1 and above by r2, and returns either r1 or r2 according to unsignedRoundingMode. It performs the following steps when called:

    1. If x is r1, return r1.
    2. Assert: unsignedRoundingMode is half-even.
    3. Let cardinality be (r1 / (r2 – r1)) modulo 2.
    4. If cardinality is 0, return r1.
    5. Return r2.

    16.5.19 PartitionNumberRangePattern ( numberFormat, x, y )

    The abstract operation PartitionNumberRangePattern takes arguments numberFormat (an Intl.NumberFormat), x (an Intl mathematical value), and y (an Intl mathematical value) and returns either a throw completion. It creates the parts for a localized number range according to x, y, and the formatting options of numberFormat. It performs the following steps when called:

    1. If x is not-a-number or y is not-a-number, throw a RangeError exception.
    2. Let xResult be PartitionNumberPattern(numberFormat, x).
    3. Let yResult be PartitionNumberPattern(numberFormat, y).
    4. If FormatNumeric(numberFormat, x) is FormatNumeric(numberFormat, y), then
      1. Let appxResult be FormatApproximately(numberFormat, xResult).
      2. For each element r of appxResult, do
        1. Set r.[[Source]] to "shared".
      3. Return appxResult.
    5. Let result be a new empty Record { [[Type]]: r.[[Type]], [[Value]]: r.[[Value]], [[Source]]: "endRange" } to result.
  • Return CollapseNumberRange(numberFormat, result).
    •

    16.5.20 FormatApproximately ( numberFormat, result )

    The abstract operation FormatApproximately takes arguments numberFormat (an Intl.NumberFormat) and result (a Records with fields [[Type]] (a String) and [[Value]] (a String). It modifies result, which must be a Record for the approximately sign, which may depend on numberFormat. It performs the following steps when called:

    1. Let approximatelySign be an ILND String value used to signify that a number is approximate.
    2. If approximatelySign is not empty, insert the Record might be inserted before the first element of result.
    3. Return result.

    16.5.21 CollapseNumberRange ( numberFormat, result )

    The List of List. The algorithm is ILND, but must not introduce ambiguity that would cause the result of Intl.NumberFormat.prototype.formatRange ( start, end ) with arguments Lists would not be equal with a trivial implementation of CollapseNumberRange that always returns result unmodified.

    For example, an implementation may remove the List representing "$3–$5" into one representing "$3–5".

    An implementation may also modify List representing "0.5 miles–1 mile" into one representing "0.5–1 miles".

    Returning result unmodified is guaranteed to be a correct implementation of CollapseNumberRange.

    16.5.22 FormatNumericRange ( numberFormat, x, y )

    The abstract operation FormatNumericRange takes arguments numberFormat (an Intl.NumberFormat), x (an Intl mathematical value), and y (an Intl mathematical value) and returns either a throw completion. It performs the following steps when called:

    1. Let parts be ? PartitionNumberRangePattern(numberFormat, x, y).
    2. Let result be the empty String.
    3. For each element part of parts, do
      1. Set result to the string-concatenation of result and part.[[Value]].
    4. Return result.

    16.5.23 FormatNumericRangeToParts ( numberFormat, x, y )

    The abstract operation FormatNumericRangeToParts takes arguments numberFormat (an Intl.NumberFormat), x (an Intl mathematical value), and y (an Intl mathematical value) and returns either a throw completion. It performs the following steps when called:

    1. Let parts be ? PartitionNumberRangePattern(numberFormat, x, y).
    2. Let result be ! CreateDataPropertyOrThrow(O, "type", part.[[Type]]).
    3. Perform ! ToString(𝔽(n)), O).
    4. Increment n by 1.
  • Return result.
    •

    17 PluralRules Objects

    17.1 The Intl.PluralRules Constructor

    The Intl.PluralRules constructor:

    • is %Intl.PluralRules%.
    • is the initial value of the "PluralRules" property of the Intl object.

    Behaviour common to all service constructor properties of the Intl object is specified in 9.1.

    17.1.1 Intl.PluralRules ( [ locales [ , options ] ] )

    When the Intl.PluralRules function is called with optional arguments locales and options, the following steps are taken:

    1. If NewTarget is undefined, throw a TypeError exception.
    2. Let pluralRules be ? OrdinaryCreateFromConstructor(NewTarget, "%Intl.PluralRules.prototype%", « [[InitializedPluralRules]], [[Locale]], [[Type]], [[Notation]], [[CompactDisplay]], [[MinimumIntegerDigits]], [[MinimumFractionDigits]], [[MaximumFractionDigits]], [[MinimumSignificantDigits]], [[MaximumSignificantDigits]], [[RoundingType]], [[RoundingIncrement]], [[RoundingMode]], [[ComputedRoundingPriority]], [[TrailingZeroDisplay]] »).
    3. Let optionsResolution be ? ResolveOptions(%Intl.PluralRules%, %Intl.PluralRules%.[[LocaleData]], locales, options, « coerce-options »).
    4. Set options to optionsResolution.[[Options]].
    5. Let r be optionsResolution.[[ResolvedLocale]].
    6. Set pluralRules.[[Locale]] to r.[[Locale]].
    7. Let t be ? GetOption(options, "type", string, « "cardinal", "ordinal" », "cardinal").
    8. Set pluralRules.[[Type]] to t.
    9. Let notation be ? GetOption(options, "notation", string, « "standard", "scientific", "engineering", "compact" », "standard").
    10. Set pluralRules.[[Notation]] to notation.
    11. Let compactDisplay be ? GetOption(options, "compactDisplay", string, « "short", "long" », "short").
    12. Set pluralRules.[[CompactDisplay]] to compactDisplay.
    13. Perform ? SetNumberFormatDigitOptions(pluralRules, options, 0, 3, notation).
    14. Return pluralRules.

    17.2 Properties of the Intl.PluralRules Constructor

    The Intl.PluralRules constructor:

    • has a [[Prototype]] internal slot whose value is %Function.prototype%.
    • has the following properties:

    17.2.1 Intl.PluralRules.prototype

    The value of Intl.PluralRules.prototype is %Intl.PluralRules.prototype%.

    This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.

    17.2.2 Intl.PluralRules.supportedLocalesOf ( locales [ , options ] )

    When the supportedLocalesOf method is called with arguments locales and options, the following steps are taken:

    1. Let availableLocales be %Intl.PluralRules%.[[AvailableLocales]].
    2. Let requestedLocales be ? CanonicalizeLocaleList(locales).
    3. Return ? FilterLocales(availableLocales, requestedLocales, options).

    17.2.3 Internal slots

    The value of the [[AvailableLocales]] internal slot is implementation-defined within the constraints described in 9.1.

    The value of the [[RelevantExtensionKeys]] internal slot is « ».

    The value of the [[ResolutionOptionDescriptors]] internal slot is « ».

    Note 1
    Unicode Technical Standard #35 Part 1 Core, Section 3.6.1 Key and Type Definitions describes no locale extension keys that are relevant to the pluralization process.

    The value of the [[LocaleData]] internal slot is implementation-defined within the constraints described in 9.1.

    Note 2
    It is recommended that implementations use the locale data provided by the Common Locale Data Repository (available at https://cldr.unicode.org/).

    17.3 Properties of the Intl.PluralRules Prototype Object

    The Intl.PluralRules prototype object:

    • is %Intl.PluralRules.prototype%.
    • is an ordinary object.
    • is not an Intl.PluralRules instance and does not have an [[InitializedPluralRules]] internal slot or any of the other internal slots of Intl.PluralRules instance objects.
    • has a [[Prototype]] internal slot whose value is %Object.prototype%.

    17.3.1 Intl.PluralRules.prototype.constructor

    The initial value of Intl.PluralRules.prototype.constructor is %Intl.PluralRules%.

    17.3.2 Intl.PluralRules.prototype.resolvedOptions ( )

    This function provides access to the locale and options computed during initialization of the object.

    1. Let pr be the this value.
    2. Perform ? List of Strings containing all possible results of PluralRuleSelect for the selected locale pr.[[Locale]], sorted according to the following order: "zero", "one", "two", "few", "many", "other".
    3. For each row of Table 30, except the header row, in table order, do
      1. Let p be the Property value of the current row.
      2. If p is "pluralCategories", then
        1. Let v be CreateDataPropertyOrThrow(options, p, v).
    4. Return options.
    Table 30: Resolved Options of PluralRules Instances
    Internal Slot Property Conversion
    [[Locale]] "locale"
    [[Type]] "type"
    [[Notation]] "notation"
    [[CompactDisplay]] "compactDisplay"
    [[MinimumIntegerDigits]] "minimumIntegerDigits" number
    [[MinimumFractionDigits]] "minimumFractionDigits" number
    [[MaximumFractionDigits]] "maximumFractionDigits" number
    [[MinimumSignificantDigits]] "minimumSignificantDigits" number
    [[MaximumSignificantDigits]] "maximumSignificantDigits" number
    "pluralCategories"
    [[RoundingIncrement]] "roundingIncrement" number
    [[RoundingMode]] "roundingMode"
    [[ComputedRoundingPriority]] "roundingPriority"
    [[TrailingZeroDisplay]] "trailingZeroDisplay"

    17.3.3 Intl.PluralRules.prototype.select ( value )

    When the select method is called with an argument value, the following steps are taken:

    1. Let pr be the this value.
    2. Perform ? ToNumber(value).
    3. Return ResolvePlural(pr, n).[[PluralCategory]].

    17.3.4 Intl.PluralRules.prototype.selectRange ( start, end )

    When the selectRange method is called with arguments start and end, the following steps are taken:

    1. Let pr be the this value.
    2. Perform ? ToNumber(end).
    3. Return ? ResolvePluralRange(pr, x, y).

    17.3.5 Intl.PluralRules.prototype [ %Symbol.toStringTag% ]

    The initial value of the %Symbol.toStringTag% property is the String value "Intl.PluralRules".

    This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

    17.4 Properties of Intl.PluralRules Instances

    Intl.PluralRules instances are ordinary objects that inherit properties from %Intl.PluralRules.prototype%.

    Intl.PluralRules instances have an [[InitializedPluralRules]] internal slot.

    Intl.PluralRules instances also have several internal slots that are computed by The Intl.PluralRules Constructor:

    • [[Locale]] is a String value with the language tag of the locale whose localization is used by the plural rules.
    • [[Type]] is one of the String values "cardinal" or "ordinal", identifying the plural rules used.
    • [[Notation]] is one of the String values "standard", "scientific", "engineering", or "compact", identifying the notation used.
    • [[CompactDisplay]] is one of the String values "short" or "long", specifying whether to display compact notation affixes in short form ("5K") or long form ("5 thousand") if formatting with the "compact" notation, as this can in some cases influence plural form selection. It is only used when [[Notation]] has the value "compact".
    • [[MinimumIntegerDigits]] is a non-negative integer digits to be used.
    • [[MinimumFractionDigits]] and [[MaximumFractionDigits]] are non-negative integers indicating the minimum and maximum fraction digits to be used. Numbers will be rounded or padded with trailing zeroes if necessary.
    • [[MinimumSignificantDigits]] and [[MaximumSignificantDigits]] are positive integer and fraction digits.
    • [[RoundingType]] is one of the values fraction-digits, significant-digits, more-precision, or less-precision, indicating which rounding strategy to use, as discussed in 16.4.
    • [[ComputedRoundingPriority]] is one of the String values "auto", "morePrecision", or "lessPrecision". It is only used in 17.3.2 to convert [[RoundingType]] back to a valid "roundingPriority" option.
    • [[RoundingIncrement]] is an integer that evenly divides 10, 100, 1000, or 10000 into tenths, fifths, quarters, or halves. It indicates the increment at which rounding should take place relative to the calculated rounding magnitude. For example, if [[MaximumFractionDigits]] is 2 and [[RoundingIncrement]] is 5, then formatted numbers are rounded to the nearest 0.05 ("nickel rounding").
    • [[RoundingMode]] identifies the rounding mode to use.
    • [[TrailingZeroDisplay]] is one of the String values "auto" or "stripIfInteger", indicating whether to strip trailing zeros if the formatted number is an integer (i.e., has no non-zero fraction digit).

    17.5 Abstract Operations for PluralRules Objects

    17.5.1 PluralRuleSelect ( locale, type, notation, compactDisplay, s )

    The implementation-defined abstract operation PluralRuleSelect takes arguments locale (a language tag), type ("cardinal" or "ordinal"), notation (a String), compactDisplay ("short" or "long"), and s (a decimal String) and returns "zero", "one", "two", "few", "many", or "other". The returned String characterizes the plural category of s according to type, notation, and compactDisplay for the corresponding locale.

    17.5.2 ResolvePlural ( pluralRules, n )

    The abstract operation ResolvePlural takes arguments pluralRules (an Intl.PluralRules) and n (a Number) and returns a Record contains two string-valued fields describing n according to the effective locale and the options of pluralRules: [[PluralCategory]] characterizing its plural category, and [[FormattedString]] containing its formatted representation. It performs the following steps when called:

    1. If n is not a ℝ(n)).
    2. Let s be res.[[FormattedString]].
    3. Let locale be pluralRules.[[Locale]].
    4. Let type be pluralRules.[[Type]].
    5. Let notation be pluralRules.[[Notation]].
    6. Let compactDisplay be pluralRules.[[CompactDisplay]].
    7. Let p be PluralRuleSelect(locale, type, notation, compactDisplay, s).
    8. Return the Record { [[PluralCategory]]: p, [[FormattedString]]: s }.

    17.5.3 PluralRuleSelectRange ( locale, type, notation, compactDisplay, xp, yp )

    The implementation-defined abstract operation PluralRuleSelectRange takes arguments locale (a language tag), type ("cardinal" or "ordinal"), notation (a String), compactDisplay ("short" or "long"), xp ("zero", "one", "two", "few", "many", or "other"), and yp ("zero", "one", "two", "few", "many", or "other") and returns "zero", "one", "two", "few", "many", or "other". It performs an implementation-dependent algorithm to map the plural category String values xp and yp, respectively characterizing the start and end of a range, to a resolved String value for the plural form of the range as a whole denoted by type, notation, and compactDisplay for the corresponding locale, or the String value "other".

    17.5.4 ResolvePluralRange ( pluralRules, x, y )

    The abstract operation ResolvePluralRange takes arguments pluralRules (an Intl.PluralRules), x (a Number), and y (a Number) and returns either a throw completion. The returned String value represents the plural form of the range starting from x and ending at y according to the effective locale and the options of pluralRules. It performs the following steps when called:

    1. If x is NaN or y is NaN, throw a RangeError exception.
    2. Let xp be ResolvePlural(pluralRules, x).
    3. Let yp be ResolvePlural(pluralRules, y).
    4. If xp.[[FormattedString]] is yp.[[FormattedString]], then
      1. Return xp.[[PluralCategory]].
    5. Let locale be pluralRules.[[Locale]].
    6. Let type be pluralRules.[[Type]].
    7. Let notation be pluralRules.[[Notation]].
    8. Let compactDisplay be pluralRules.[[CompactDisplay]].
    9. Return PluralRuleSelectRange(locale, type, notation, compactDisplay, xp.[[PluralCategory]], yp.[[PluralCategory]]).

    18 RelativeTimeFormat Objects

    18.1 The Intl.RelativeTimeFormat Constructor

    The Intl.RelativeTimeFormat constructor:

    • is %Intl.RelativeTimeFormat%.
    • is the initial value of the "RelativeTimeFormat" property of the Intl object.

    Behaviour common to all service constructor properties of the Intl object is specified in 9.1.

    18.1.1 Intl.RelativeTimeFormat ( [ locales [ , options ] ] )

    When the Intl.RelativeTimeFormat function is called with optional arguments locales and options, the following steps are taken:

    1. If NewTarget is undefined, throw a TypeError exception.
    2. Let relativeTimeFormat be ? Construct(%Intl.NumberFormat%, « locale, nfOptions »).
    3. Let relativeTimeFormat.[[PluralRules]] be ! Construct(%Intl.PluralRules%, « locale »).
    4. Return relativeTimeFormat.

    18.2 Properties of the Intl.RelativeTimeFormat Constructor

    The Intl.RelativeTimeFormat constructor:

    • has a [[Prototype]] internal slot whose value is %Function.prototype%.
    • has the following properties:

    18.2.1 Intl.RelativeTimeFormat.prototype

    The value of Intl.RelativeTimeFormat.prototype is %Intl.RelativeTimeFormat.prototype%.

    This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.

    18.2.2 Intl.RelativeTimeFormat.supportedLocalesOf ( locales [ , options ] )

    When the supportedLocalesOf method is called with arguments locales and options, the following steps are taken:

    1. Let availableLocales be %Intl.RelativeTimeFormat%.[[AvailableLocales]].
    2. Let requestedLocales be ? CanonicalizeLocaleList(locales).
    3. Return ? FilterLocales(availableLocales, requestedLocales, options).

    18.2.3 Internal slots

    The value of the [[AvailableLocales]] internal slot is implementation-defined within the constraints described in 9.1.

    The value of the [[RelevantExtensionKeys]] internal slot is « "nu" ».

    The value of the [[ResolutionOptionDescriptors]] internal slot is « { [[Key]]: "nu", [[Property]]: "numberingSystem" } ».

    Note 1
    Unicode Technical Standard #35 Part 1 Core, Section 3.6.1 Key and Type Definitions describes one locale extension key that is relevant to relative time formatting: "nu" for numbering system (of formatted numbers).

    The value of the [[LocaleData]] internal slot is implementation-defined within the constraints described in 9.1 and the following additional constraints, for all locale values locale:

    • [[LocaleData]].[[<locale>]] has fields "second", "minute", "hour", "day", "week", "month", "quarter", and "year". Additional fields may exist with the previous names concatenated with the strings "-narrow" or "-short". The values corresponding to these fields are Records which contain these two categories of fields:
      • "future" and "past" fields, which are Records with a field for each of the plural categories relevant for locale. The value corresponding to those fields is a pattern which may contain "{0}" to be replaced by a formatted number.
      • Optionally, additional fields whose key is the result of ToString of a Number, and whose values are literal Strings which are not treated as templates.
    • The List that is the value of the "nu" field of any locale field of [[LocaleData]] must not include the values "native", "traditio", or "finance".
    Note 2
    It is recommended that implementations use the locale data provided by the Common Locale Data Repository (available at https://cldr.unicode.org/).

    18.3 Properties of the Intl.RelativeTimeFormat Prototype Object

    The Intl.RelativeTimeFormat prototype object:

    • is %Intl.RelativeTimeFormat.prototype%.
    • is an ordinary object.
    • is not an Intl.RelativeTimeFormat instance and does not have an [[InitializedRelativeTimeFormat]] internal slot or any of the other internal slots of Intl.RelativeTimeFormat instance objects.
    • has a [[Prototype]] internal slot whose value is %Object.prototype%.

    18.3.1 Intl.RelativeTimeFormat.prototype.constructor

    The initial value of Intl.RelativeTimeFormat.prototype.constructor is %Intl.RelativeTimeFormat%.

    18.3.2 Intl.RelativeTimeFormat.prototype.resolvedOptions ( )

    This function provides access to the locale and options computed during initialization of the object.

    1. Let relativeTimeFormat be the this value.
    2. Perform ? Assert: v is not undefined.
    3. Perform ! CreateDataPropertyOrThrow(options, p, v).
  • Return options.
    •
    Table 31: Resolved Options of RelativeTimeFormat Instances
    Internal Slot Property
    [[Locale]] "locale"
    [[Style]] "style"
    [[Numeric]] "numeric"
    [[NumberingSystem]] "numberingSystem"

    18.3.3 Intl.RelativeTimeFormat.prototype.format ( value, unit )

    When the format method is called with arguments value and unit, the following steps are taken:

    1. Let relativeTimeFormat be the this value.
    2. Perform ? ToString(unit).
    3. Return ? FormatRelativeTime(relativeTimeFormat, value, unit).

    18.3.4 Intl.RelativeTimeFormat.prototype.formatToParts ( value, unit )

    When the formatToParts method is called with arguments value and unit, the following steps are taken:

    1. Let relativeTimeFormat be the this value.
    2. Perform ? ToString(unit).
    3. Return ? FormatRelativeTimeToParts(relativeTimeFormat, value, unit).

    18.3.5 Intl.RelativeTimeFormat.prototype [ %Symbol.toStringTag% ]

    The initial value of the %Symbol.toStringTag% property is the String value "Intl.RelativeTimeFormat".

    This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

    18.4 Properties of Intl.RelativeTimeFormat Instances

    Intl.RelativeTimeFormat instances are ordinary objects that inherit properties from %Intl.RelativeTimeFormat.prototype%.

    Intl.RelativeTimeFormat instances have an [[InitializedRelativeTimeFormat]] internal slot.

    Intl.RelativeTimeFormat instances also have several internal slots that are computed by The Intl.RelativeTimeFormat Constructor:

    • [[Locale]] is a String value with the language tag of the locale whose localization is used for formatting.
    • [[LocaleData]] is a Record representing the data available to the implementation for formatting. It is the value of an entry in %Intl.RelativeTimeFormat%.[[LocaleData]] associated with either the value of [[Locale]] or a prefix thereof.
    • [[Style]] is one of the String values "long", "short", or "narrow", identifying the relative time format style used.
    • [[Numeric]] is one of the String values "always" or "auto", identifying whether numerical descriptions are always used, or used only when no more specific version is available (e.g., "1 day ago" vs "yesterday").
    • [[NumberFormat]] is an Intl.NumberFormat object used for formatting.
    • [[NumberingSystem]] Unicode Number System Identifier used for formatting.
    • [[PluralRules]] is an Intl.PluralRules object used for formatting.

    18.5 Abstract Operations for RelativeTimeFormat Objects

    18.5.1 SingularRelativeTimeUnit ( unit )

    The abstract operation SingularRelativeTimeUnit takes argument unit (a String) and returns either a throw completion. It performs the following steps when called:

    1. If unit is "seconds", return "second".
    2. If unit is "minutes", return "minute".
    3. If unit is "hours", return "hour".
    4. If unit is "days", return "day".
    5. If unit is "weeks", return "week".
    6. If unit is "months", return "month".
    7. If unit is "quarters", return "quarter".
    8. If unit is "years", return "year".
    9. If unit is not one of "second", "minute", "hour", "day", "week", "month", "quarter", or "year", throw a RangeError exception.
    10. Return unit.

    18.5.2 PartitionRelativeTimePattern ( relativeTimeFormat, value, unit )

    The abstract operation PartitionRelativeTimePattern takes arguments relativeTimeFormat (an Intl.RelativeTimeFormat), value (a Number), and unit (a String) and returns either a throw completion. The returned List represents value according to the effective locale and the formatting options of relativeTimeFormat. It performs the following steps when called:

    1. If value is NaN, +∞𝔽, or -∞𝔽, throw a RangeError exception.
    2. Let unit be ? SingularRelativeTimeUnit(unit).
    3. Let fields be relativeTimeFormat.[[LocaleData]].
    4. Let patterns be fields.[[<unit>]].
    5. Let style be relativeTimeFormat.[[Style]].
    6. If style is "short" or "narrow", then
      1. Let key be the Record { [[Type]]: "literal", [[Value]]: result, [[Unit]]: empty }.
  • If value is -0𝔽 or value < -0𝔽, then
    1. Let tl be "past".
  • Else,
    1. Let tl be "future".
  • Let po be patterns.[[<tl>]].
  • Let fv be PartitionNumberPattern(relativeTimeFormat.[[NumberFormat]], ℝ(value)).
  • Let pr be ResolvePlural(relativeTimeFormat.[[PluralRules]], value).[[PluralCategory]].
  • Let pattern be po.[[<pr>]].
  • Return MakePartsList(pattern, unit, fv).
    •

    18.5.3 MakePartsList ( pattern, unit, parts )

    The abstract operation MakePartsList takes arguments pattern (a Pattern String), unit (a String), and parts (a Records with fields [[Type]] (a String), [[Value]] (a String), and [[Unit]] (a String or empty). It performs the following steps when called:

    1. Let patternParts be PartitionPattern(pattern).
    2. Let result be a new empty Assert: patternPart.[[Type]] is "0".
    3. For each Record { [[Type]]: part.[[Type]], [[Value]]: part.[[Value]], [[Unit]]: unit } to result.
  • Return result.
    •  Note
    Example:
    1. Return MakePartsList("AA{0}BB", "hour", « Record { [[Type]]: "integer", [[Value]]: "15" } »).
     will return a Records like « { [[Type]]: "literal", [[Value]]: "AA", [[Unit]]: empty}, { [[Type]]: "integer", [[Value]]: "15", [[Unit]]: "hour"}, { [[Type]]: "literal", [[Value]]: "BB", [[Unit]]: empty} »

    18.5.4 FormatRelativeTime ( relativeTimeFormat, value, unit )

    The abstract operation FormatRelativeTime takes arguments relativeTimeFormat (an Intl.RelativeTimeFormat), value (a Number), and unit (a String) and returns either a throw completion. It performs the following steps when called:

    1. Let parts be ? PartitionRelativeTimePattern(relativeTimeFormat, value, unit).
    2. Let result be the empty String.
    3. For each string-concatenation of result and part.[[Value]].
  • Return result.
    •

    18.5.5 FormatRelativeTimeToParts ( relativeTimeFormat, value, unit )

    The abstract operation FormatRelativeTimeToParts takes arguments relativeTimeFormat (an Intl.RelativeTimeFormat), value (a Number), and unit (a String) and returns either a throw completion. It performs the following steps when called:

    1. Let parts be ? PartitionRelativeTimePattern(relativeTimeFormat, value, unit).
    2. Let result be ! %Object.prototype%).
    3. Perform ! CreateDataPropertyOrThrow(result, ! 𝔽(n)), O).
    4. Increment n by 1.
  • Return result.
    •

    19 Segmenter Objects

    19.1 The Intl.Segmenter Constructor

    The Intl.Segmenter constructor:

    • is %Intl.Segmenter%.
    • is the initial value of the "Segmenter" property of the Intl object.

    Behaviour common to all service constructor properties of the Intl object is specified in 9.1.

    19.1.1 Intl.Segmenter ( [ locales [ , options ] ] )

    When the Intl.Segmenter function is called with optional arguments locales and options, the following steps are taken:

    1. If NewTarget is undefined, throw a TypeError exception.
    2. Let internalSlotsList be « [[InitializedSegmenter]], [[Locale]], [[SegmenterGranularity]] ».
    3. Let segmenter be ? OrdinaryCreateFromConstructor(NewTarget, "%Intl.Segmenter.prototype%", internalSlotsList).
    4. Let optionsResolution be ? ResolveOptions(%Intl.Segmenter%, %Intl.Segmenter%.[[LocaleData]], locales, options).
    5. Set options to optionsResolution.[[Options]].
    6. Let r be optionsResolution.[[ResolvedLocale]].
    7. Set segmenter.[[Locale]] to r.[[Locale]].
    8. Let granularity be ? GetOption(options, "granularity", string, « "grapheme", "word", "sentence" », "grapheme").
    9. Set segmenter.[[SegmenterGranularity]] to granularity.
    10. Return segmenter.

    19.2 Properties of the Intl.Segmenter Constructor

    The Intl.Segmenter constructor:

    • has a [[Prototype]] internal slot whose value is %Function.prototype%.
    • has the following properties:

    19.2.1 Intl.Segmenter.prototype

    The value of Intl.Segmenter.prototype is %Intl.Segmenter.prototype%.

    This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.

    19.2.2 Intl.Segmenter.supportedLocalesOf ( locales [ , options ] )

    When the supportedLocalesOf method is called with arguments locales and options, the following steps are taken:

    1. Let availableLocales be %Intl.Segmenter%.[[AvailableLocales]].
    2. Let requestedLocales be ? CanonicalizeLocaleList(locales).
    3. Return ? FilterLocales(availableLocales, requestedLocales, options).

    19.2.3 Internal slots

    The value of the [[AvailableLocales]] internal slot is implementation-defined within the constraints described in 9.1.

    The value of the [[RelevantExtensionKeys]] internal slot is « ».

    The value of the [[ResolutionOptionDescriptors]] internal slot is « ».

    Note
    Intl.Segmenter does not have any relevant extension keys.

    The value of the [[LocaleData]] internal slot is implementation-defined within the constraints described in 9.1.

    19.3 Properties of the Intl.Segmenter Prototype Object

    The Intl.Segmenter prototype object:

    • is %Intl.Segmenter.prototype%.
    • is an ordinary object.
    • is not an Intl.Segmenter instance and does not have an [[InitializedSegmenter]] internal slot or any of the other internal slots of Intl.Segmenter instance objects.
    • has a [[Prototype]] internal slot whose value is %Object.prototype%.

    19.3.1 Intl.Segmenter.prototype.constructor

    The initial value of Intl.Segmenter.prototype.constructor is %Intl.Segmenter%.

    19.3.2 Intl.Segmenter.prototype.resolvedOptions ( )

    This function provides access to the locale and options computed during initialization of the object.

    1. Let segmenter be the this value.
    2. Perform ? Assert: v is not undefined.
    3. Perform ! CreateDataPropertyOrThrow(options, p, v).
  • Return options.
    •
    Table 32: Resolved Options of Segmenter Instances
    Internal Slot Property
    [[Locale]] "locale"
    [[SegmenterGranularity]] "granularity"

    19.3.3 Intl.Segmenter.prototype.segment ( string )

    The Intl.Segmenter.prototype.segment method is called on an Intl.Segmenter instance with argument string to create a Segments instance for the string using the locale and options of the Intl.Segmenter instance. The following steps are taken:

    1. Let segmenter be the this value.
    2. Perform ? ToString(string).
    3. Return CreateSegmentsObject(segmenter, string).

    19.3.4 Intl.Segmenter.prototype [ %Symbol.toStringTag% ]

    The initial value of the %Symbol.toStringTag% property is the String value "Intl.Segmenter".

    This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

    19.4 Properties of Intl.Segmenter Instances

    Intl.Segmenter instances are ordinary objects that inherit properties from %Intl.Segmenter.prototype%.

    Intl.Segmenter instances have an [[InitializedSegmenter]] internal slot.

    Intl.Segmenter instances also have internal slots that are computed by The Intl.Segmenter Constructor:

    • [[Locale]] is a String value with the language tag of the locale whose localization is used for segmentation.
    • [[SegmenterGranularity]] is one of the String values "grapheme", "word", or "sentence", identifying the kind of text element to segment.

    19.5 Segments Objects

    A Segments instance is an object that represents the segments of a specific string, subject to the locale and options of its constructing Intl.Segmenter instance.

    19.5.1 CreateSegmentsObject ( segmenter, string )

    The abstract operation CreateSegmentsObject takes arguments segmenter (an Intl.Segmenter) and string (a String) and returns a Segments instance. The Segments instance references segmenter and string. It performs the following steps when called:

    1. Let internalSlotsList be « [[SegmentsSegmenter]], [[SegmentsString]] ».
    2. Let segments be OrdinaryObjectCreate(%IntlSegmentsPrototype%, internalSlotsList).
    3. Set segments.[[SegmentsSegmenter]] to segmenter.
    4. Set segments.[[SegmentsString]] to string.
    5. Return segments.

    19.5.2 The %IntlSegmentsPrototype% Object

    The %IntlSegmentsPrototype% object:

    • is the prototype of all Segments objects.
    • is an ordinary object.
    • has a [[Prototype]] internal slot whose value is %Object.prototype%.
    • has the following properties:

    19.5.2.1 %IntlSegmentsPrototype%.containing ( index )

    The containing method is called on a Segments instance with argument index to return a Segment Data object describing the segment in the string including the code unit at the specified index according to the locale and options of the Segments instance's constructing Intl.Segmenter instance. The following steps are taken:

    1. Let segments be the this value.
    2. Perform ? ToIntegerOrInfinity(index).
    3. If n < 0 or n ≥ len, return undefined.
    4. Let startIndex be FindBoundary(segmenter, string, n, before).
    5. Let endIndex be FindBoundary(segmenter, string, n, after).
    6. Return CreateSegmentDataObject(segmenter, string, startIndex, endIndex).

    19.5.2.2 %IntlSegmentsPrototype% [ %Symbol.iterator% ] ( )

    The %Symbol.iterator% method is called on a Segments instance to create a Segment Iterator over its string using the locale and options of its constructing Intl.Segmenter instance. The following steps are taken:

    1. Let segments be the this value.
    2. Perform ? RequireInternalSlot(segments, [[SegmentsSegmenter]]).
    3. Let segmenter be segments.[[SegmentsSegmenter]].
    4. Let string be segments.[[SegmentsString]].
    5. Return CreateSegmentIterator(segmenter, string).

    The value of the "name" property of this function is "[Symbol.iterator]".

    19.5.3 Properties of Segments Instances

    Segments instances are ordinary objects that inherit properties from %IntlSegmentsPrototype%.

    Segments instances have a [[SegmentsSegmenter]] internal slot that references the constructing Intl.Segmenter instance.

    Segments instances have a [[SegmentsString]] internal slot that references the String value whose segments they expose.

    19.6 Segment Iterator Objects

    A Segment Iterator is an object that represents a particular iteration over the segments of a specific string.

    19.6.1 CreateSegmentIterator ( segmenter, string )

    The abstract operation CreateSegmentIterator takes arguments segmenter (an Intl.Segmenter) and string (a String) and returns a Segment Iterator. The Segment Iterator iterates over string using the locale and options of segmenter. It performs the following steps when called:

    1. Let internalSlotsList be « [[IteratingSegmenter]], [[IteratedString]], [[IteratedStringNextSegmentCodeUnitIndex]] ».
    2. Let iterator be OrdinaryObjectCreate(%IntlSegmentIteratorPrototype%, internalSlotsList).
    3. Set iterator.[[IteratingSegmenter]] to segmenter.
    4. Set iterator.[[IteratedString]] to string.
    5. Set iterator.[[IteratedStringNextSegmentCodeUnitIndex]] to 0.
    6. Return iterator.

    19.6.2 The %IntlSegmentIteratorPrototype% Object

    The %IntlSegmentIteratorPrototype% object:

    19.6.2.1 %IntlSegmentIteratorPrototype%.next ( )

    The next method is called on a Segment Iterator instance to advance it forward one segment and return an IteratorResult object either describing the new segment or declaring iteration done. The following steps are taken:

    1. Let iterator be the this value.
    2. Perform ? CreateIteratorResultObject(segmentData, false).

    19.6.2.2 %IntlSegmentIteratorPrototype% [ %Symbol.toStringTag% ]

    The initial value of the %Symbol.toStringTag% property is the String value "Segmenter String Iterator".

    This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

    19.6.3 Properties of Segment Iterator Instances

    Segment Iterator instances are ordinary objects that inherit properties from %SegmentIteratorPrototype%. Segment Iterator instances are initially created with the internal slots described in Table 33.

    Table 33: Internal Slots of Segment Iterator Instances
    Internal Slot Description
    [[IteratingSegmenter]] The Intl.Segmenter instance used for iteration.
    [[IteratedString]] The String value being iterated upon.
    [[IteratedStringNextSegmentCodeUnitIndex]] The code unit index in the String value being iterated upon at the start of the next segment.

    19.7 Segment Data Objects

    A Segment Data object is an object that represents a particular segment from a string.

    19.7.1 CreateSegmentDataObject ( segmenter, string, startIndex, endIndex )

    The abstract operation CreateSegmentDataObject takes arguments segmenter (an Intl.Segmenter), string (a String), startIndex (a non-negative integer) and returns a Segment Data object. The Segment Data object describes the segment within string from segmenter that is bounded by the indices startIndex and endIndex. It performs the following steps when called:

    1. Let len be the length of string.
    2. %Object.prototype%).
    3. Let segment be the 𝔽(startIndex)).
    4. Perform ! CreateDataPropertyOrThrow(result, "isWordLike", isWordLike).
  • Return result.
    •  Note
    Whether a segment is "word-like" is implementation-dependent, and implementations are recommended to use locale-sensitive tailorings. In general, segments consisting solely of spaces and/or punctuation (such as those terminated with "WORD_NONE" boundaries by ICU [International Components for Unicode, documented at

    19.8 Abstract Operations for Segmenter Objects

    19.8.1 FindBoundary ( segmenter, string, startIndex, direction )

    The abstract operation FindBoundary takes arguments segmenter (an Intl.Segmenter), string (a String), startIndex (a non-negative integer. It finds a segmentation boundary between two code units in string in the specified direction from the code unit at index startIndex according to the locale and options of segmenter and returns the immediately following code unit index. It performs the following steps when called:

    1. Let len be the length of string.
    2. Assert: direction is after.
    3. Search string for the first segmentation boundary that follows the code unit at index startIndex, using locale locale and text element granularity granularity.
    4. If a boundary is found, return the count of code units in string preceding it.
    5. Return len.
     Note
    Boundary determination is implementation-dependent, but general default algorithms are specified in https://cldr.unicode.org).

    20 Locale Sensitive Functions of the ECMAScript Language Specification

    ECMA-262 describes several locale-sensitive functions. An ECMAScript implementation that implements this specification shall implement these functions as described here.

    Note
    The Collator, NumberFormat, or DateTimeFormat objects created in the algorithms in this clause are only used within these algorithms. They are never directly accessed by ECMAScript code and need not actually exist within an implementation.

    20.1 Properties of the String Prototype Object

    20.1.1 String.prototype.localeCompare ( that [ , locales [ , options ] ] )

    This definition supersedes the definition provided in ECMA-262, 22.1.3.12.

    When the localeCompare method is called with argument that and optional arguments locales, and options, the following steps are taken:

    1. Let O be ? Construct(%Intl.Collator%, « locales, options »).
    2. Return CompareStrings(collator, S, thatValue).

    The "length" property of this function is 1𝔽.

    Note 1
    The localeCompare method itself is not directly suitable as an argument to Array.prototype.sort because the latter requires a function of two arguments.
    Note 2
    The localeCompare function is intentionally generic; it does not require that its this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a method.

    20.1.2 String.prototype.toLocaleLowerCase ( [ locales ] )

    This definition supersedes the definition provided in ECMA-262, 22.1.3.26.

    This function interprets a String value as a sequence of code points, as described in ECMA-262, 6.1.4. The following steps are taken:

    1. Let O be ? ToString(O).
    2. Return ? TransformCase(S, locales, lower).
     Note
    The toLocaleLowerCase function is intentionally generic; it does not require that its this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a method.

    20.1.2.1 TransformCase ( S, locales, targetCase )

    The abstract operation TransformCase takes arguments S (a String), locales (an 6.1.4, and returns the result of ILD transformation into targetCase as a new String value. It performs the following steps when called:

    1. Let requestedLocales be ? CanonicalizeLocaleList(locales).
    2. If requestedLocales is not an empty Assert: targetCase is upper.
    3. Let newCodePoints be a CodePointsToString(newCodePoints).

    Code point mappings may be derived according to a tailored version of the Default Case Conversion Algorithms of the Unicode Standard. Implementations may use locale-sensitive tailoring defined in the file SpecialCasing.txt of the Unicode Character Database and/or CLDR and/or any other custom tailoring. Regardless of tailoring, a conforming implementation's case transformation algorithm must always yield the same result given the same input code points, locale, and target case.

    Note
    The case mapping of some code points may produce multiple code points, and therefore the result may not be the same length as the input. Because both toLocaleUpperCase and toLocaleLowerCase have context-sensitive behaviour, the functions are not symmetrical. In other words, s.toLocaleUpperCase().toLocaleLowerCase() is not necessarily equal to s.toLocaleLowerCase() and s.toLocaleLowerCase().toLocaleUpperCase() is not necessarily equal to s.toLocaleUpperCase().

    20.1.3 String.prototype.toLocaleUpperCase ( [ locales ] )

    This definition supersedes the definition provided in ECMA-262, 22.1.3.27.

    This function interprets a String value as a sequence of code points, as described in ECMA-262, 6.1.4. The following steps are taken:

    1. Let O be ? ToString(O).
    2. Return ? TransformCase(S, locales, upper).
     Note
    The toLocaleUpperCase function is intentionally generic; it does not require that its this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a method.

    20.2 Properties of the Number Prototype Object

    The following definition(s) refer to the abstract operation thisNumberValue as defined in ECMA-262, 21.1.3.

    20.2.1 Number.prototype.toLocaleString ( [ locales [ , options ] ] )

    This definition supersedes the definition provided in ECMA-262, 21.1.3.4.

    When the toLocaleString method is called with optional arguments locales and options, the following steps are taken:

    1. Let x be ? Construct(%Intl.NumberFormat%, « locales, options »).
    2. Return FormatNumeric(numberFormat, ! ToIntlMathematicalValue(x)).

    20.3 Properties of the BigInt Prototype Object

    The following definition(s) refer to the abstract operation thisBigIntValue as defined in ECMA-262, 21.2.3.

    20.3.1 BigInt.prototype.toLocaleString ( [ locales [ , options ] ] )

    This definition supersedes the definition provided in ECMA-262, 21.2.3.2.

    When the toLocaleString method is called with optional arguments locales and options, the following steps are taken:

    1. Let x be ? ℝ(x)).

    20.4 Properties of the Date Prototype Object

    The following definition(s) refer to the abstract operation thisTimeValue as defined in ECMA-262, 21.4.4.

    20.4.1 Date.prototype.toLocaleString ( [ locales [ , options ] ] )

    This definition supersedes the definition provided in ECMA-262, 21.4.4.39.

    When the toLocaleString method is called with optional arguments locales and options, the following steps are taken:

    1. Let dateObject be the this value.
    2. Perform ? RequireInternalSlot(dateObject, [[DateValue]]).
    3. Let x be dateObject.[[DateValue]].
    4. If x is NaN, return "Invalid Date".
    5. Let dateFormat be ? CreateDateTimeFormat(%Intl.DateTimeFormat%, locales, options, any, all).
    6. Return ! FormatDateTime(dateFormat, x).

    20.4.2 Date.prototype.toLocaleDateString ( [ locales [ , options ] ] )

    This definition supersedes the definition provided in Date.prototype.toLocaleDateString ( [ reserved1 [ , reserved2 ] ] ).

    When the toLocaleDateString method is called with optional arguments locales and options, the following steps are taken:

    1. Let dateObject be the this value.
    2. Perform ? RequireInternalSlot(dateObject, [[DateValue]]).
    3. Let x be dateObject.[[DateValue]].
    4. If x is NaN, return "Invalid Date".
    5. Let dateFormat be ? CreateDateTimeFormat(%Intl.DateTimeFormat%, locales, options, date, date).
    6. Return ! FormatDateTime(dateFormat, x).

    20.4.3 Date.prototype.toLocaleTimeString ( [ locales [ , options ] ] )

    This definition supersedes the definition provided in Date.prototype.toLocaleTimeString ( [ reserved1 [ , reserved2 ] ] ).

    When the toLocaleTimeString method is called with optional arguments locales and options, the following steps are taken:

    1. Let dateObject be the this value.
    2. Perform ? RequireInternalSlot(dateObject, [[DateValue]]).
    3. Let x be dateObject.[[DateValue]].
    4. If x is NaN, return "Invalid Date".
    5. Let timeFormat be ? CreateDateTimeFormat(%Intl.DateTimeFormat%, locales, options, time, time).
    6. Return ! FormatDateTime(timeFormat, x).

    20.5 Properties of the Array Prototype Object

    20.5.1 Array.prototype.toLocaleString ( [ locales [ , options ] ] )

    This definition supersedes the definition provided in Array.prototype.toLocaleString ( [ reserved1 [ , reserved2 ] ] ).

    When the toLocaleString method is called with optional arguments locales and options, the following steps are taken:

    1. Let array be ? host environment's current locale (such as ", ").
    2. Let R be the empty String.
    3. Let k be 0.
    4. Repeat, while k < len,
      1. If k > 0, then
        1. Set R to the 𝔽(k))).
        2. If nextElement is not undefined or null, then
          1. Let S be ? string-concatenation of R and S.
        3. Set k to k + 1.
      2. Return R.
      Note 1
      This algorithm's steps mirror the steps taken in Invoke(nextElement, "toLocaleString") now takes locales and options as arguments.
      Note 2
      The elements of the array are converted to Strings using their toLocaleString methods, and these Strings are then concatenated, separated by occurrences of an host environment's current locale.
      Note 3
      The toLocaleString function is intentionally generic; it does not require that its this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method.

      Annex A (informative) Implementation Dependent Behaviour

      The following aspects of this specification are implementation dependent:

      • In all functionality:
      • In Collator:
        • Support for the Unicode extensions keys "kf", "kn" and the parallel options properties "caseFirst", "numeric" (10.1.1)
        • The set of supported "co" key values (collations) per locale beyond a default collation (10.2.3)
        • The set of supported "kf" key values (case order) per locale (10.2.3)
        • The set of supported "kn" key values (numeric collation) per locale (10.2.3)
        • The default search sensitivity per locale (10.2.3)
        • The default ignore punctuation value per locale (10.2.3)
        • The sort order for each supported locale and options combination (10.3.3.1)
      • In DateTimeFormat:
        • The BestFitFormatMatcher algorithm (11.1.2)
        • The set of supported "ca" key values (calendars) per locale (11.2.3)
        • The set of supported "nu" key values (numbering systems) per locale (11.2.3)
        • The default hourCycle setting per locale (11.2.3)
        • The set of supported date-time formats per locale beyond a core set, including the representations used for each component and the associated patterns (11.2.3)
        • Localized weekday names, era names, month names, day period names, am/pm indicators, and time zone names (11.5.5)
        • The calendric calculations used for calendars other than "gregory" (11.5.12)
        • The set of all known registered Zone and Link names of the IANA Time Zone Database and the information about their offsets from UTC and their daylight saving time rules (21.4.1.19)
      • In DisplayNames:
        • The localized names (12.2.3)
      • In DurationFormat:
        • The set of supported "nu" key values (numbering systems) per locale (13.2.3)
        • The digital formatting configuration (use of two-digit hours with style "numeric" and separators for numeric hours, minutes, and seconds) per locale (13.2.3)
      • In ListFormat:
        • The patterns used for formatting values (14.2.3)
      • In Locale:
        • Support for the Unicode extensions keys "kf", "kn" and the parallel options properties "caseFirst", "numeric" (15.1.1)
      • In NumberFormat:
        • The set of supported "nu" key values (numbering systems) per locale (16.2.3)
        • The patterns used for formatting values as decimal, percent, currency, or unit values per locale, with or without the sign, with or without accounting format for currencies, and in standard, compact, or scientific notation (16.5.6)
        • The number of fractional digits used when formatting currency values (16.5.6)
        • Localized representations of NaN and Infinity (16.5.6)
        • The implementation of numbering systems not listed in Table 28 (16.5.6)
        • Localized decimal and grouping separators (16.5.6)
        • Localized plus and minus signs (16.5.6)
        • Localized digit grouping schemata (16.5.6)
        • Localized magnitude thresholds for compact notation (16.5.6)
        • Localized symbols for compact and scientific notation (16.5.6)
        • Localized narrow, short, and long currency symbols and names (16.5.6)
        • Localized narrow, short, and long unit symbols (16.5.6)
      • In PluralRules:
        • List of Strings representing the possible results of plural selection and their corresponding order per locale. (17.1.1)
      • In RelativeTimeFormat:
        • The set of supported "nu" key values (numbering systems) per locale (18.2.3)
        • The patterns used for formatting values (18.2.3)
      • In Segmenter:
        • Boundary determination algorithms (19.8.1)
        • Classification of segments as "word-like" (19.7.1)

      Annex B (informative) Additions and Changes That Introduce Incompatibilities with Prior Editions

      • 10.1, 16.1, 11.1 In ECMA-402, 1st Edition, constructors could be used to create Intl objects from arbitrary objects. This is no longer possible in 2nd Edition.
      • 11.3.3 In ECMA-402, 1st Edition, the "length" property of the function object F was set to +0𝔽. In 2nd Edition, "length" is set to 1𝔽.
      • 10.3.4 In ECMA-402, 7th Edition, the %Symbol.toStringTag% is set to "Intl.Collator".
      • 11.3.7 In ECMA-402, 7th Edition, the %Symbol.toStringTag% is set to "Intl.DateTimeFormat".
      • 16.3.7 In ECMA-402, 7th Edition, the %Symbol.toStringTag% is set to "Intl.NumberFormat".
      • 17.3.5 In ECMA-402, 7th Edition, the %Symbol.toStringTag% is set to "Intl.PluralRules".
      • 8.1.1 In ECMA-402, 7th Edition, the %Symbol.toStringTag% is set to "Intl".
      • 16.1 In ECMA-402, 8th Edition, the NumberFormat constructor used to throw an error when style is "currency" and maximumFractionDigits was set to a value lower than the default fractional digits for that currency. This behaviour was corrected in the 9th edition, and it no longer throws an error.

      Annex C (informative) Colophon

      This specification is authored on Ecmarkdown for authoring algorithm steps. PDF renderings of this specification are produced by printing the HTML rendering to a PDF.

      Prior editions of this specification were authored using Word—the Ecmarkup source text that formed the basis of this edition was produced by converting the ECMAScript 2015 Word document to Ecmarkup using an automated conversion tool.

      Copyright & Software License

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