ECMA-402

7th Edition / June 2020

ECMAScript® 2020 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 2020 Internationalization API Specification (ECMA-402 7th Edition), provides key language sensitive functionality as a complement to the ECMAScript 2020 Language Specification (ECMA-262 11th Edition or successor). Its functionality has been selected from that of well-established internationalization APIs such as those of the Internationalization Components for Unicode (ICU) library, of the .NET framework, or of the Java platform.

The 1st Edition API was developed by an ad-hoc group established by Ecma TC39 in September 2010 based on a proposal by Nebojša Ćirić and Jungshik Shin.

The 2nd Edition API was adopted by the General Assembly of June 2015, as a complement to the ECMAScript 6th Edition.

The 3rd Edition API was the first edition released under Ecma TC39's new yearly release cadence and open development process. A plain-text source document was built from the ECMA-402 source document to serve as the base for further development entirely on GitHub. Over the year of this standard's development, dozens of pull requests and issues were filed representing several of bug fixes, editorial fixes and other improvements. Additionally, numerous software tools were developed to aid in this effort including Ecmarkup, Ecmarkdown, and Grammarkdown.

Dozens of individuals representing many organizations have made very significant contributions within Ecma TC39 to the development of this edition and to the prior editions. In addition, a vibrant community has emerged supporting TC39's ECMAScript efforts. This community has reviewed numerous drafts, filed dozens of bug reports, performed implementation experiments, contributed test suites, and educated the world-wide developer community about ECMAScript Internationalization. Unfortunately, it is impossible to identify and acknowledge every person and organization who has contributed to this effort.

Norbert Lindenberg
ECMA-402, 1st Edition Project Editor

Rick Waldron
ECMA-402, 2nd Edition Project Editor

Caridy Patiño
ECMA-402, 3rd, 4th and 5th Editions Project Editor

Caridy Patiño, Daniel Ehrenberg, Leo Balter
ECMA-402, 6th Edition Project Editors

Leo Balter, Valerie Young, Isaac Durazo
ECMA-402, 7th Edition Project Editors

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 the ECMAScript 2020 Internationalization API Specification must conform to the ECMAScript 2020 Language Specification (ECMA-262 11th Edition, or successor), and must provide and support all the objects, properties, functions, and program semantics described in this specification.

A conforming implementation of the ECMAScript 2020 Internationalization API Specification is permitted to provide additional objects, properties, and functions beyond those described in this specification. In particular, a conforming implementation of the ECMAScript 2020 Internationalization API Specification is permitted to provide properties not described in this specification, and values for those properties, for objects that are described in this specification. 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:

  • The options property "localeMatcher" in all constructors and supportedLocalesOf methods.
  • The options properties "usage" and "sensitivity" in the Collator constructor.
  • The options properties "style" and "currencyDisplay" in the NumberFormat constructor.
  • The options properties "minimumIntegerDigits", "minimumFractionDigits", "maximumFractionDigits", "minimumSignificantDigits", and "maximumSignificantDigits" in the NumberFormat constructor, provided that the additional values are interpreted as integer values higher than the specified limits.
  • The options properties listed in Table 6 in the DateTimeFormat constructor.
  • The options property "formatMatcher" in the DateTimeFormat constructor.
  • The options property "type" in the PluralRules constructor.

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 2020 Language Specification (ECMA-262 11th Edition, or successor).
https://www.ecma-international.org/publications-and-standards/standards/ecma-262/

Note
Throughout this document, the phrase “ES2020, x” (where x is a sequence of numbers separated by periods) may be used as shorthand for "ECMAScript 2020 Language Specification (ECMA-262 11th Edition, sub clause x)".

4 Overview

This section contains a non-normative overview of the ECMAScript 2020 Internationalization API Specification.

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.

The ECMAScript 2020 Language Specification 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. The ECMAScript 2020 Internationalization API Specification builds on this 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

The ECMAScript 2020 Internationalization API Specification is designed to complement the ECMAScript 2020 Language Specification by providing key language-sensitive functionality. The API can be added to an implementation of the ECMAScript 2020 Language Specification (ECMA-262 11th Edition, or successor).

The ECMAScript 2020 Internationalization API Specification provides several key pieces of language-sensitive functionality that are required in most applications: String comparison (collation), number formatting, date and time formatting, pluralization rules, and case conversion. While the ECMAScript 2020 Language Specification provides functions for this basic functionality (on Array.prototype: toLocaleString; on String.prototype: localeCompare, toLocaleLowerCase, toLocaleUpperCase; on Number.prototype: toLocaleString; on Date.prototype: toLocaleString, toLocaleDateString, and toLocaleTimeString), it leaves the actual behaviour of these functions largely up to implementations to define. The ECMAScript 2020 Internationalization API 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 the constructors Intl.Collator, Intl.NumberFormat, Intl.DateTimeFormat, or Intl.PluralRules to construct an object, specifying a list of preferred languages and options to configure the behaviour of the resulting object. The object then provides a main function (compare, select, or format), 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 the ECMAScript 2020 Language Specification 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 the ECMAScript 2020 Internationalization API Specification to avoid name collisions.

4.3 Implementation Dependencies

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

  • The set of locales that an implementation supports with adequate localizations: Linguists estimate the number of human languages to around 6000, and the more widely spoken ones have variations based on regions or other parameters. Even large locale data collections, such as the Common Locale Data Repository, cover only a subset of this large set. 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.

4.3.1 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 the ECMAScript 2020 Language Specification (ECMA-262 11th Edition), as ES2020:

  • Object Internal Methods and Internal Slots, as described in ES2020, 6.1.7.2.
  • Algorithm conventions, as described in ES2020, 5.2, and the use of abstract operations, as described in ES2020, 7.1, 7.2, 7.3.
  • Internal Slots, as described in ES2020, 9.1.
  • The List and Record Specification Type, as described in ES2020, 6.2.1.
Note
As described in the ECMAScript Language Specification, 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 Normative Optional to denote the sense of Annex B in ECMA 262. That is, normative optional sections are required when the ECMAScript host is a web browser. The content of the section is normative but optional if the ECMAScript host is not a web browser.

5.1 Well-Known Intrinsic Objects

The following table extends the Well-Known Intrinsic Objects table defined in ES2020, 6.1.7.4.

Table 1: Well-known Intrinsic Objects (Extensions)
Intrinsic Name Global Name ECMAScript Language Association
%Collator% Intl.Collator The Intl.Collator constructor (11.1)
%CollatorPrototype% Intl.Collator.prototype The initial value of the "prototype" data property of the intrinsic %Collator% (11.2.1).
%Date_now% Date.now The initial value of the "now" data property of the intrinsic %Date% (ES2020, 20.4.3.1)
%DateTimeFormat% Intl.DateTimeFormat The Intl.DateTimeFormat constructor (13.2).
%DateTimeFormatPrototype% Intl.DateTimeFormat.prototype The initial value of the "prototype" data property of the intrinsic %DateTimeFormat% (13.3.1).
%Intl% Intl The Intl object (8).
%Locale% Intl.Locale The Intl.Locale constructor (10.1).
%LocalePrototype% Intl.Locale.prototype The initial value of the prototype data property of the intrinsic %Locale% (10.2.1).
%NumberFormat% Intl.NumberFormat The Intl.NumberFormat constructor (12.2)
%NumberFormatPrototype% Intl.NumberFormat.prototype The initial value of the "prototype" data property of the intrinsic %NumberFormat% (12.3.1).
%PluralRules% Intl.PluralRules The Intl.PluralRules constructor (15.2).
%PluralRulesPrototype% Intl.PluralRules.prototype The initial value of the "prototype" data property of the intrinsic %PluralRules% (15.3.1).
%RelativeTimeFormat% Intl.RelativeTimeFormat The Intl.RelativeTimeFormat constructor (14.2).
%RelativeTimeFormatPrototype% Intl.RelativeTimeFormat.prototype The initial value of the prototype data property of the intrinsic %RelativeTimeFormat% (14.3.1).
%StringProto_indexOf% String.prototype.indexOf The initial value of the "indexOf" data property of the intrinsic %StringPrototype% (ES2020, 21.1.3.8)

6 Identification of Locales, Currencies, Time Zones, and Measurement Units

This clause describes the String values used in the ECMAScript 2020 Internationalization API Specification to identify locales, currencies, time zones, and measurement units.

6.1 Case Sensitivity and Case Mapping

The String values used to identify locales, currencies, and time zones are interpreted in a case-insensitive manner, treating the Unicode Basic Latin characters "A" to "Z" (U+0041 to U+005A) as equivalent to the corresponding Basic Latin characters "a" to "z" (U+0061 to U+007A). No other case folding equivalences are applied. When mapping to upper case, a mapping shall be used that maps characters in the range "a" to "z" (U+0061 to U+007A) to the corresponding characters in the range "A" to "Z" (U+0041 to U+005A) and maps no other characters to the latter range.

EXAMPLES "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).

6.2 Language Tags

The ECMAScript 2020 Internationalization API Specification identifies locales using Unicode BCP 47 locale identifiers as defined by Unicode Technical Standard #35 LDML § 3 Unicode Language and Locale Identifiers, which may include extensions such as the Unicode BCP 47 U Extension. Their canonical form is specified in Unicode Technical Standard #35 LDML § 3.2.1 Canonical Unicode Locale Identifiers.

Unicode BCP 47 locale identifiers are structurally valid when they match those syntactical formatting criteria of Unicode Technical Standard 35, section 3.2, but it is not required to validate them according to the Unicode validation data. All structurally valid language tags are valid for use with the APIs defined by this standard. However, the set of locales and thus language tags that an implementation supports with adequate localizations is implementation dependent. The constructors Collator, NumberFormat, DateTimeFormat, and PluralRules map the language tags used in requests to locales supported by their respective implementations.

6.2.1 Unicode Locale Extension Sequences

This standard uses the term "Unicode locale extension sequence" - as described in unicode_locale_extensions in UTS 35 Unicode Locale Identifier, section 3.2 - for any substring of a language tag that is not part of a private use subtag sequence, starts with a separator "-" and the singleton "u", and includes the maximum sequence of following non-singleton subtags and their preceding "-" separators.

6.2.2 IsStructurallyValidLanguageTag ( locale )

The IsStructurallyValidLanguageTag abstract operation verifies that the locale argument (which must be a String value)

  • represents a well-formed "Unicode BCP 47 locale identifier" as specified in Unicode Technical Standard 35 section 3.2,
  • does not include duplicate variant subtags, and
  • does not include duplicate singleton subtags.

The abstract operation returns true if locale can be generated from the EBNF grammar in section 3.2 of the Unicode Technical Standard 35, starting with unicode_locale_id, and does not contain duplicate variant or singleton subtags (other than as a private use subtag). It returns false otherwise. Terminal value characters in the grammar are interpreted as the Unicode equivalents of the ASCII octet values given.

6.2.3 CanonicalizeUnicodeLocaleId ( locale )

The CanonicalizeUnicodeLocaleId abstract operation returns the canonical and case-regularized form of the locale argument (which must be a String value that is a structurally valid Unicode BCP 47 locale identifier as verified by the IsStructurallyValidLanguageTag abstract operation). The following steps are taken:

  1. Let localeId be the string locale after performing the algorithm to transform it to canonical syntax per Unicode Technical Standard #35 LDML § 3.2.1 Canonical Unicode Locale Identifiers. (The result is a Unicode BCP 47 locale identifier, in canonical syntax but not necessarily in canonical form.)
  2. Let localeId be the string localeId after performing the algorithm to transform it to canonical form. (The result is a Unicode BCP 47 locale identifier, in both canonical syntax and canonical form.)
  3. If localeId contains a substring extension that is a Unicode locale extension sequence, then
    1. Let components be ! UnicodeExtensionComponents(extension).
    2. Let attributes be components.[[Attributes]].
    3. Let keywords be components.[[Keywords]].
    4. Let newExtension be "u".
    5. For each element attr of attributes in List order, do
      1. Append "-" to newExtension.
      2. Append attr to newExtension.
    6. For each element keyword of keywords in List order, do
      1. Append "-" to newExtension.
      2. Append keyword.[[Key]] to newExtension.
      3. If keyword.[[Value]] is not the empty String, then
        1. Append "-" to newExtension.
        2. Append keyword.[[Value]] to newExtension.
    7. Assert: newExtension is not equal to "u".
    8. Let localeId be localeId with the substring corresponding to extension replaced by the string newExtension.
  4. Return localeId.
Note
The third step of this algorithm 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.

6.2.4 DefaultLocale ()

The DefaultLocale abstract operation returns a String value representing the structurally valid (6.2.2) and canonicalized (6.2.3) Unicode BCP 47 locale identifier for the host environment's current locale.

6.3 Currency Codes

The ECMAScript 2020 Internationalization API Specification identifies currencies using 3-letter currency codes as defined by ISO 4217. Their canonical form is upper case.

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 IsWellFormedCurrencyCode abstract operation verifies that the currency argument (which must be a String value) represents a well-formed 3-letter ISO currency code. The following steps are taken:

  1. Let normalized be the result of mapping currency to upper case as described in 6.1.
  2. If the number of elements in normalized is not 3, return false.
  3. If normalized contains any character that is not in the range "A" to "Z" (U+0041 to U+005A), return false.
  4. Return true.

6.4 Time Zone Names

The ECMAScript 2020 Internationalization API Specification identifies time zones using the Zone and Link names of the IANA Time Zone Database. Their canonical form is the corresponding Zone name in the casing used in the IANA Time Zone Database.

All registered Zone and Link names are allowed. Implementations must recognize all such names, and use best available current and historical information about their offsets from UTC and their daylight saving time rules in calculations. However, the set of combinations of time zone name and language tag for which localized time zone names are available is implementation dependent.

6.4.1 IsValidTimeZoneName ( timeZone )

The IsValidTimeZoneName abstract operation verifies that the timeZone argument (which must be a String value) represents a valid Zone or Link name of the IANA Time Zone Database.

The abstract operation returns true if timeZone, converted to upper case as described in 6.1, is equal to one of the Zone or Link names of the IANA Time Zone Database, converted to upper case as described in 6.1. It returns false otherwise.

6.4.2 CanonicalizeTimeZoneName

The CanonicalizeTimeZoneName abstract operation returns the canonical and case-regularized form of the timeZone argument (which must be a String value that is a valid time zone name as verified by the IsValidTimeZoneName abstract operation). The following steps are taken:

  1. Let ianaTimeZone be the Zone or Link name of the IANA Time Zone Database such that timeZone, converted to upper case as described in 6.1, is equal to ianaTimeZone, converted to upper case as described in 6.1.
  2. If ianaTimeZone is a Link name, let ianaTimeZone be the corresponding Zone name as specified in the "backward" file of the IANA Time Zone Database.
  3. If ianaTimeZone is "Etc/UTC" or "Etc/GMT", return "UTC".
  4. Return ianaTimeZone.

The Intl.DateTimeFormat constructor allows this time zone name; if the time zone is not specified, the host environment's current time zone is used. Implementations shall support UTC and the host environment's current time zone (if different from UTC) in formatting.

6.4.3 DefaultTimeZone ()

The DefaultTimeZone abstract operation returns a String value representing the valid (6.4.1) and canonicalized (6.4.2) time zone name for the host environment's current time zone.

6.5 Measurement Unit Identifiers

The ECMAScript 2020 Internationalization API Specification identifies measurement units using a core unit identifier as defined by Unicode Technical Standard #35, Part 2, Section 6. Their canonical form is a string containing all lowercase letters with zero or more hyphens.

Only a limited set of core unit identifiers are allowed. An illegal core unit identifier results in a RangeError.

6.5.1 IsWellFormedUnitIdentifier ( unitIdentifier )

The IsWellFormedUnitIdentifier abstract operation verifies that the unitIdentifier argument (which must be a String value) represents a well-formed core unit identifier as defined in UTS #35, Part 2, Section 6. In addition to obeying the UTS #35 core unit identifier syntax, unitIdentifier must be one of the identifiers sanctioned by UTS #35 or be a compound unit composed of two sanctioned simple units. The following steps are taken:

  1. If the result of IsSanctionedSimpleUnitIdentifier(unitIdentifier) is true, then
    1. Return true.
  2. If the substring "-per-" does not occur exactly once in unitIdentifier, then
    1. Return false.
  3. Let numerator be the substring of unitIdentifier from the beginning to just before "-per-".
  4. If the result of IsSanctionedSimpleUnitIdentifier(numerator) is false, then
    1. Return false.
  5. Let denominator be the substring of unitIdentifier from just after "-per-" to the end.
  6. If the result of IsSanctionedSimpleUnitIdentifier(denominator) is false, then
    1. Return false.
  7. Return true.

6.5.2 IsSanctionedSimpleUnitIdentifier ( unitIdentifier )

The IsSanctionedSimpleUnitIdentifier abstract operation verifies that the given core unit identifier is among the simple units sanctioned in the current version of the ECMAScript Internationalization API Specification, a subset of the Validity Data as described in UTS #35, Part 1, Section 3.11; the list may grow over time. As discussed in UTS #35, a simple unit is one that does not have a numerator and denominator. The following steps are taken:

  1. If unitIdentifier is listed in Table 2 below, return true.
  2. Else, Return false.
Table 2: Simple units sanctioned for use in ECMAScript
Simple Unit
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
mile
mile-scandinavian
milliliter
millimeter
millisecond
minute
month
ounce
percent
petabyte
pound
second
stone
terabit
terabyte
week
yard
year

7 Requirements for Standard Built-in ECMAScript Objects

Unless specified otherwise in this document, the objects, functions, and constructors described in this standard are subject to the generic requirements and restrictions specified for standard built-in ECMAScript objects in the ECMAScript 2020 Language Specification, 11th edition, clause 17, or successor.

8 The Intl Object

The Intl object is the %Intl% intrinsic object and the initial value of the "Intl" property of the global object. The Intl object is a single ordinary object.

The value of the [[Prototype]] internal slot of the Intl object is the intrinsic object %ObjectPrototype%.

The Intl object is not a function object. It does not have a [[Construct]] internal method; it is not possible to use the Intl object as a constructor with the new operator. The Intl object does not have a [[Call]] internal method; it is not possible to invoke the Intl object as a function.

The Intl object has an internal slot, [[FallbackSymbol]], which is a new %Symbol% in the current realm with the [[Description]] "IntlLegacyConstructedSymbol".

8.1 Constructor Properties of the Intl Object

8.1.1 Intl.Locale (...)

See 10.

8.1.2 Intl.Collator (...)

See 11.

8.1.3 Intl.NumberFormat (...)

See 12.

8.1.4 Intl.DateTimeFormat (...)

See 13.

8.1.5 Intl.RelativeTimeFormat (...)

See 14.

8.1.6 Intl.PluralRules (...)

See 15.

Note
In ECMA 402 v1, Intl constructors supported a mode of operation where calling them with an existing object as a receiver would transform the receiver into the relevant Intl instance with all internal slots. In ECMA 402 v2, this capability was removed, to avoid adding internal slots on existing objects. In ECMA 402 v3, the capability was re-added as "normative optional" in a mode which chains the underlying Intl instance on any object, when the constructor is called. See Issue 57 for details.

8.2 Function Properties of the Intl Object

8.2.1 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).

9 Locale and Parameter Negotiation

The constructors for the objects providing locale sensitive services, Collator, NumberFormat, DateTimeFormat, PluralRules, and RelativeTimeFormat, use a common pattern to negotiate the requests represented by the locales and options arguments against the actual capabilities of their implementations. The common behaviour is described here in terms of internal slots describing the capabilities and of abstract operations using these internal slots.

9.1 Internal slots of Service Constructors

The constructors Intl.Collator, Intl.NumberFormat, Intl.DateTimeFormat, Intl.PluralRules, and Intl.RelativeTimeFormat have the following internal slots:

  • [[AvailableLocales]] is a List that contains structurally valid (6.2.2) and canonicalized (6.2.3) Unicode BCP 47 locale identifiers identifying the locales for which the implementation provides the functionality of the constructed objects. Language tags on the list must not have a Unicode locale extension sequence. The list must include the value returned by the DefaultLocale abstract operation (6.2.4), and must not include duplicates. Implementations must include in [[AvailableLocales]] locales that can serve as fallbacks in the algorithm used to resolve locales (see 9.2.7). For example, implementations that provide a "de-DE" locale must include a "de" locale that can serve as a fallback for requests such as "de-AT" and "de-CH". For locales that in current usage would include a script subtag (such as Chinese locales), old-style language tags without script subtags must be included such that, for example, requests for "zh-TW" and "zh-HK" lead to output in traditional Chinese rather than the default simplified Chinese. The ordering of the locales within [[AvailableLocales]] is irrelevant.
  • [[RelevantExtensionKeys]] is a List of keys of the language tag extensions defined in Unicode Technical Standard 35 that are relevant for the functionality of the constructed objects.
  • [[SortLocaleData]] and [[SearchLocaleData]] (for Intl.Collator) and [[LocaleData]] (for Intl.NumberFormat, Intl.DateTimeFormat, Intl.PluralRules, and Intl.RelativeTimeFormat) are records that have fields for each locale contained in [[AvailableLocales]]. The value of each of these fields must be a record that has fields for each key contained in [[RelevantExtensionKeys]]. The value of each of these fields must be a non-empty list of those values defined in Unicode Technical Standard 35 for the given key that are supported by the implementation for the given locale, with the first element providing the default value.

EXAMPLE An implementation of DateTimeFormat might include the language tag "th" in its [[AvailableLocales]] internal slot, and must (according to 13.3.3) include the key "ca" in its [[RelevantExtensionKeys]] internal slot. For Thai, the "buddhist" calendar is usually the default, but an implementation might also support the calendars "gregory", "chinese", and "islamicc" for the locale "th". The [[LocaleData]] internal slot would therefore at least include {[[th]]: {[[ca]]: « "buddhist", "gregory", "chinese", "islamicc" »}}.

9.2 Abstract Operations

Where the following abstract operations take an availableLocales argument, it must be an [[AvailableLocales]] List as specified in 9.1.

9.2.1 CanonicalizeLocaleList ( locales )

The abstract operation CanonicalizeLocaleList takes the following steps:

  1. If locales is undefined, then
    1. Return a new empty List.
  2. Let seen be a new empty List.
  3. If Type(locales) is String or Type(locales) is Object and locales has an [[InitializedLocale]] internal slot, then
    1. Let O be CreateArrayFromList(« locales »).
  4. Else,
    1. Let O be ? ToObject(locales).
  5. Let len be ? ToLength(? Get(O, "length")).
  6. Let k be 0.
  7. Repeat, while k < len
    1. Let Pk be ToString(k).
    2. Let kPresent be ? HasProperty(O, Pk).
    3. If kPresent is true, then
      1. Let kValue be ? Get(O, Pk).
      2. If Type(kValue) is not String or Object, throw a TypeError exception.
      3. If Type(kValue) is Object and kValue has an [[InitializedLocale]] internal slot, then
        1. Let tag be kValue.[[Locale]].
      4. Else,
        1. Let tag be ? ToString(kValue).
      5. If IsStructurallyValidLanguageTag(tag) is false, throw a RangeError exception.
      6. Let canonicalizedTag be CanonicalizeUnicodeLocaleId(tag).
      7. If canonicalizedTag is not an element of seen, append canonicalizedTag as the last element of seen.
    4. Increase k by 1.
  8. 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 BestAvailableLocale ( availableLocales, locale )

The BestAvailableLocale abstract operation compares the provided argument locale, which must be a String value with a structurally valid and canonicalized Unicode BCP 47 locale identifier, against the locales in availableLocales and returns either the longest non-empty prefix of locale that is an element of availableLocales, or undefined if there is no such element. It uses the fallback mechanism of RFC 4647, section 3.4. The following steps are taken:

  1. Let candidate be locale.
  2. Repeat,
    1. If availableLocales contains an element equal to candidate, return candidate.
    2. Let pos be the character index of the last occurrence of "-" (U+002D) within candidate. If that character does not occur, return undefined.
    3. If pos ≥ 2 and the character "-" occurs at index pos-2 of candidate, decrease pos by 2.
    4. Let candidate be the substring of candidate from position 0, inclusive, to position pos, exclusive.

9.2.3 LookupMatcher ( availableLocales, requestedLocales )

The LookupMatcher abstract operation compares requestedLocales, which must be a List as returned by CanonicalizeLocaleList, against the locales in availableLocales and determines the best available language to meet the request. The following steps are taken:

  1. Let result be a new Record.
  2. For each element locale of requestedLocales in List order, do
    1. Let noExtensionsLocale be the String value that is locale with all Unicode locale extension sequences removed.
    2. Let availableLocale be BestAvailableLocale(availableLocales, noExtensionsLocale).
    3. If availableLocale is not undefined, then
      1. Set result.[[locale]] to availableLocale.
      2. If locale and noExtensionsLocale are not the same String value, then
        1. Let extension be the String value consisting of the first substring of locale that is a Unicode locale extension sequence.
        2. Set result.[[extension]] to extension.
      3. Return result.
  3. Let defLocale be DefaultLocale().
  4. Set result.[[locale]] to defLocale.
  5. Return result.
Note
The algorithm is based on the Lookup algorithm described in RFC 4647 section 3.4, but options specified through Unicode locale extension sequences are ignored in the lookup. Information about such subsequences is returned separately. The abstract operation returns a record with a [[locale]] field, whose value is the language tag of the selected locale, which must be an element of availableLocales. If the language tag of the request locale that led to the selected locale contained a Unicode locale extension sequence, then the returned record also contains an [[extension]] field whose value is the first Unicode locale extension sequence within the request locale language tag.

9.2.4 BestFitMatcher ( availableLocales, requestedLocales )

The BestFitMatcher abstract operation compares requestedLocales, which must be a List as returned by CanonicalizeLocaleList, against the locales in availableLocales and determines the best available language to meet the request. The algorithm is implementation dependent, but should produce results that a typical user of the requested locales would perceive as at least as good as those produced by the LookupMatcher abstract operation. Options specified through Unicode locale extension sequences must be ignored by the algorithm. Information about such subsequences is returned separately. The abstract operation returns a record with a [[locale]] field, whose value is the language tag of the selected locale, which must be an element of availableLocales. If the language tag of the request locale that led to the selected locale contained a Unicode locale extension sequence, then the returned record also contains an [[extension]] field whose value is the first Unicode locale extension sequence within the request locale language tag.

9.2.5 UnicodeExtensionComponents( extension )

The UnicodeExtensionComponents abstract operation returns the attributes and keywords from extension, which must be a Unicode locale extension sequence. If an attribute or a keyword occurs multiple times in extension, only the first occurence is returned. The following steps are taken:

  1. Let attributes be the empty List.
  2. Let keywords be the empty List.
  3. Let isKeyword be false.
  4. Let size be the number of elements in extension.
  5. Let k be 3.
  6. Repeat, while k < size
    1. Let e be ! Call(%StringProto_indexOf%, extension, « "-", k »).
    2. If e = -1, let len be size - k; else let len be e - k.
    3. Let subtag be the String value equal to the substring of extension consisting of the code units at indices k (inclusive) through k + len (exclusive).
    4. If isKeyword is false, then
      1. If len ≠ 2 and subtag is not an element of attributes, then
        1. Append subtag to attributes.
    5. Else,
      1. If len = 2, then
        1. If keywords does not contain an element whose [[Key]] is the same as key, then
          1. Append the Record{[[Key]]: key, [[Value]]: value} to keywords.
      2. Else,
        1. If value is not the empty String, then
          1. Let value be the string-concatenation of value and "-".
        2. Let value be the string-concatenation of value and subtag.
    6. If len = 2, then
      1. Let isKeyword be true.
      2. Let key be subtag.
      3. Let value be the empty String.
    7. Let k be k + len + 1.
  7. If isKeyword is true, then
    1. If keywords does not contain an element whose [[Key]] is the same as key, then
      1. Append the Record{[[Key]]: key, [[Value]]: value} to keywords.
  8. Return the Record{[[Attributes]]: attributes, [[Keywords]]: keywords}.

9.2.6 InsertUnicodeExtensionAndCanonicalize( locale, extension )

The InsertUnicodeExtensionAndCanonicalize abstract operation inserts extension, which must be a Unicode locale extension sequence, into locale, which must be a String value with a structurally valid and canonicalized Unicode BCP 47 locale identifier. The following steps are taken:

The following algorithm refers to UTS 35's Unicode Language and Locale Identifiers grammar.

  1. Assert: locale does not contain a substring that is a Unicode locale extension sequence.
  2. Assert: extension is a Unicode locale extension sequence.
  3. Assert: tag matches the unicode_locale_id production.
  4. Let privateIndex be ! Call(%StringProto_indexOf%, locale, « "-x-" »).
  5. If privateIndex = -1, then
    1. Let locale be the string-concatenation of locale and extension.
  6. Else,
    1. Let preExtension be the substring of locale from position 0, inclusive, to position privateIndex, exclusive.
    2. Let postExtension be the substring of locale from position privateIndex to the end of the string.
    3. Let locale be the string-concatenation of preExtension, extension, and postExtension.
  7. Assert: IsStructurallyValidLanguageTag(locale) is true.
  8. Return ! CanonicalizeUnicodeLocaleId(locale).

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

The ResolveLocale abstract operation compares a BCP 47 language priority list requestedLocales against the locales in availableLocales and determines the best available language to meet the request. availableLocales, requestedLocales, and relevantExtensionKeys must be provided as List values, options and localeData as Records.

The following steps are taken:

  1. Let matcher be options.[[localeMatcher]].
  2. If matcher is "lookup", then
    1. Let r be LookupMatcher(availableLocales, requestedLocales).
  3. Else,
    1. Let r be BestFitMatcher(availableLocales, requestedLocales).
  4. Let foundLocale be r.[[locale]].
  5. Let result be a new Record.
  6. Set result.[[dataLocale]] to foundLocale.
  7. If r has an [[extension]] field, then
    1. Let components be ! UnicodeExtensionComponents(r.[[extension]]).
    2. Let keywords be components.[[Keywords]].
  8. Let supportedExtension be "-u".
  9. For each element key of relevantExtensionKeys in List order, do
    1. Let foundLocaleData be localeData.[[<foundLocale>]].
    2. Assert: Type(foundLocaleData) is Record.
    3. Let keyLocaleData be foundLocaleData.[[<key>]].
    4. Assert: Type(keyLocaleData) is List.
    5. Let value be keyLocaleData[0].
    6. Assert: Type(value) is either String or Null.
    7. Let supportedExtensionAddition be "".
    8. If r has an [[extension]] field, then
      1. If keywords contains an element whose [[Key]] is the same as key, then
        1. Let entry be the element of keywords whose [[Key]] is the same as key.
        2. Let requestedValue be entry.[[Value]].
        3. If requestedValue is not the empty String, then
          1. If keyLocaleData contains requestedValue, then
            1. Let value be requestedValue.
            2. Let supportedExtensionAddition be the string-concatenation of "-", key, "-", and value.
        4. Else if keyLocaleData contains "true", then
          1. Let value be "true".
          2. Let supportedExtensionAddition be the string-concatenation of "-" and key.
    9. If options has a field [[<key>]], then
      1. Let optionsValue be options.[[<key>]].
      2. Assert: Type(optionsValue) is either String, Undefined, or Null.
      3. If Type(optionsValue) is String, then
        1. Let optionsValue be the string optionsValue after performing the algorithm steps to transform Unicode extension values to canonical syntax per Unicode Technical Standard #35 LDML § 3.2.1 Canonical Unicode Locale Identifiers, treating key as ukey and optionsValue as uvalue productions.
        2. Let optionsValue be the string optionsValue after performing the algorithm steps to replace Unicode extension values with their canonical form per Unicode Technical Standard #35 LDML § 3.2.1 Canonical Unicode Locale Identifiers, treating key as ukey and optionsValue as uvalue productions.
        3. If optionsValue is the empty String, then
          1. Let optionsValue be "true".
      4. If keyLocaleData contains optionsValue, then
        1. If SameValue(optionsValue, value) is false, then
          1. Let value be optionsValue.
          2. Let supportedExtensionAddition be "".
    10. Set result.[[<key>]] to value.
    11. Append supportedExtensionAddition to supportedExtension.
  10. If the number of elements in supportedExtension is greater than 2, then
    1. Let foundLocale be InsertUnicodeExtensionAndCanonicalize(foundLocale, supportedExtension).
  11. Set result.[[locale]] to foundLocale.
  12. Return result.
Note
Non-normative summary: Two algorithms are available to match the locales: the Lookup algorithm described in RFC 4647 section 3.4, and an implementation dependent best-fit algorithm. Independent of the locale matching algorithm, options specified through Unicode locale extension sequences are negotiated separately, taking the caller's relevant extension keys and locale data as well as client-provided options into consideration. The abstract operation returns a record with a [[locale]] field whose value is the language tag of the selected locale, and fields for each key in relevantExtensionKeys providing the selected value for that key.

9.2.8 LookupSupportedLocales ( availableLocales, requestedLocales )

The LookupSupportedLocales abstract operation returns the subset of the provided BCP 47 language priority list requestedLocales for which availableLocales has a matching locale when using the BCP 47 Lookup algorithm. Locales appear in the same order in the returned list as in requestedLocales. The following steps are taken:

  1. Let subset be a new empty List.
  2. For each element locale of requestedLocales in List order, do
    1. Let noExtensionsLocale be the String value that is locale with all Unicode locale extension sequences removed.
    2. Let availableLocale be BestAvailableLocale(availableLocales, noExtensionsLocale).
    3. If availableLocale is not undefined, append locale to the end of subset.
  3. Return subset.

9.2.9 BestFitSupportedLocales ( availableLocales, requestedLocales )

The BestFitSupportedLocales abstract operation returns the subset of the provided BCP 47 language priority list requestedLocales for which availableLocales has a matching locale when using the Best Fit Matcher algorithm. Locales appear in the same order in the returned list as in requestedLocales. The steps taken are implementation dependent.

9.2.10 SupportedLocales ( availableLocales, requestedLocales, options )

The SupportedLocales abstract operation returns the subset of the provided BCP 47 language priority list requestedLocales for which availableLocales has a matching locale. Two algorithms are available to match the locales: the Lookup algorithm described in RFC 4647 section 3.4, and an implementation dependent best-fit algorithm. Locales appear in the same order in the returned list as in requestedLocales. The following steps are taken:

  1. If options is not undefined, then
    1. Let options be ? ToObject(options).
    2. Let matcher be ? GetOption(options, "localeMatcher", "string", « "lookup", "best fit" », "best fit").
  2. Else, let matcher be "best fit".
  3. If matcher is "best fit", then
    1. Let supportedLocales be BestFitSupportedLocales(availableLocales, requestedLocales).
  4. Else,
    1. Let supportedLocales be LookupSupportedLocales(availableLocales, requestedLocales).
  5. Return CreateArrayFromList(supportedLocales).

9.2.11 GetOption ( options, property, type, values, fallback )

The abstract operation GetOption extracts the value of the property named property from the provided options object, converts it to the required type, checks whether it is one of a List of allowed values, and fills in a fallback value if necessary. If values is undefined, there is no fixed set of values and any is permitted.

  1. Let value be ? Get(options, property).
  2. If value is not undefined, then
    1. Assert: type is "boolean" or "string".
    2. If type is "boolean", then
      1. Let value be ToBoolean(value).
    3. If type is "string", then
      1. Let value be ? ToString(value).
    4. If values is not undefined, then
      1. If values does not contain an element equal to value, throw a RangeError exception.
    5. Return value.
  3. Else, return fallback.

9.2.12 DefaultNumberOption ( value, minimum, maximum, fallback )

The abstract operation DefaultNumberOption converts value to a Number value, checks whether it is in the allowed range, and fills in a fallback value if necessary.

  1. If value is not undefined, then
    1. Let value be ? ToNumber(value).
    2. If value is NaN or less than minimum or greater than maximum, throw a RangeError exception.
    3. Return floor(value).
  2. Else, return fallback.

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

The abstract operation GetNumberOption extracts the value of the property named property from the provided options object, converts it to a Number value, checks whether it is in the allowed range, and fills in a fallback value if necessary.

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

9.2.14 PartitionPattern ( pattern )

The PartitionPattern abstract operation is called with argument pattern. This abstract operation parses an abstract pattern string into a list of Records with two fields, [[Type]] and [[Value]]. The [[Value]] field will be a String value if [[Type]] is "literal", and undefined otherwise. The syntax of the abstract pattern strings is an implementation detail and is not exposed to users of ECMA-402. The following steps are taken:

  1. Let result be a new empty List.
  2. Let beginIndex be ! Call(%StringProto_indexOf%, pattern, « "{", 0 »).
  3. Let endIndex be 0.
  4. Let nextIndex be 0.
  5. Let length be the number of code units in pattern.
  6. Repeat, while beginIndex is an integer index into pattern
    1. Set endIndex to ! Call(%StringProto_indexOf%, pattern, « "}", beginIndex »).
    2. Assert: endIndex is greater than beginIndex.
    3. If beginIndex is greater than nextIndex, then
      1. Let literal be a substring of pattern from position nextIndex, inclusive, to position beginIndex, exclusive.
      2. Append a new Record { [[Type]]: "literal", [[Value]]: literal } as the last element of the list result.
    4. Let p be the substring of pattern from position beginIndex, exclusive, to position endIndex, exclusive.
    5. Append a new Record { [[Type]]: p, [[Value]]: undefined } as the last element of the list result.
    6. Set nextIndex to endIndex + 1.
    7. Set beginIndex to ! Call(%StringProto_indexOf%, pattern, « "{", nextIndex »).
  7. If nextIndex is less than length, then
    1. Let literal be the substring of pattern from position nextIndex, inclusive, to position length, exclusive.
    2. Append a new Record { [[Type]]: "literal", [[Value]]: literal } as the last element of the list result.
  8. Return result.

10 Locale Objects

10.1 The Intl.Locale Constructor

The Locale constructor is the %Locale% intrinsic object and a standard built-in property of the Intl object.

10.1.1 ApplyOptionsToTag( tag, options )

The following algorithm refers to UTS 35's Unicode Language and Locale Identifiers grammar.

  1. Assert: Type(tag) is String.
  2. If IsStructurallyValidLanguageTag(tag) is false, throw a RangeError exception.
  3. Let language be ? GetOption(options, "language", "string", undefined, undefined).
  4. If language is not undefined, then
    1. If language does not match the unicode_language_subtag production, throw a RangeError exception.
  5. Let script be ? GetOption(options, "script", "string", undefined, undefined).
  6. If script is not undefined, then
    1. If script does not match the unicode_script_subtag production, throw a RangeError exception.
  7. Let region be ? GetOption(options, "region", "string", undefined, undefined).
  8. If region is not undefined, then
    1. If region does not match the unicode_region_subtag production, throw a RangeError exception.
  9. Set tag to CanonicalizeUnicodeLocaleId(tag).
  10. Assert: tag matches the unicode_locale_id production.
  11. Let languageId be the substring of tag corresponding to the unicode_language_id production.
  12. If language is not undefined, then
    1. Set languageId to languageId with the substring corresponding to the unicode_language_subtag production replaced by the string language.
  13. If script is not undefined, then
    1. If languageId does not contain a unicode_script_subtag production, then
      1. Set languageId to the string-concatenation of the unicode_language_subtag production of languageId, "-", script, and the rest of languageId.
    2. Else,
      1. Set languageId to languageId with the substring corresponding to the unicode_script_subtag production replaced by the string script.
  14. If region is not undefined, then
    1. If languageId does not contain a unicode_region_subtag production, then
      1. Set languageId to the string-concatenation of the unicode_language_subtag production of languageId, the substring corresponding to "-" and the unicode_script_subtag production if present, "-", region, and the rest of languageId.
    2. Else,
      1. Set languageId to languageId with the substring corresponding to the unicode_region_subtag production replaced by the string region.
  15. Set tag to tag with the substring corresponding to the unicode_language_id production replaced by the string languageId.
  16. Return CanonicalizeUnicodeLocaleId(tag).

10.1.2 ApplyUnicodeExtensionToTag( tag, options, relevantExtensionKeys )

The following algorithm refers to UTS 35's Unicode Language and Locale Identifiers grammar.

  1. Assert: Type(tag) is String.
  2. Assert: tag matches the unicode_locale_id production.
  3. If tag contains a substring that is a Unicode locale extension sequence, then
    1. Let extension be the String value consisting of the first substring of tag that is a Unicode locale extension sequence.
    2. Let components be ! UnicodeExtensionComponents(extension).
    3. Let attributes be components.[[Attributes]].
    4. Let keywords be components.[[Keywords]].
  4. Else,
    1. Let attributes be the empty List.
    2. Let keywords be the empty List.
  5. Let result be a new Record.
  6. Repeat for each element key of relevantExtensionKeys in List order,
    1. Let value be undefined.
    2. If keywords contains an element whose [[Key]] is the same as key, then
      1. Let entry be the element of keywords whose [[Key]] is the same as key.
      2. Let value be entry.[[Value]].
    3. Else
      1. Let entry be empty.
    4. Assert: options has a field [[<key>]].
    5. Let optionsValue be options.[[<key>]].
    6. If optionsValue is not undefined, then
      1. Assert: Type(optionsValue) is String.
      2. Let value be optionsValue.
      3. If entry is not empty, then
        1. Set entry.[[Value]] to value.
      4. Else,
        1. Append the Record{[[Key]]: key, [[Value]]: value} to keywords.
    7. Set result.[[<key>]] to value.
  7. Let locale be the String value that is tag with all Unicode locale extension sequences removed.
  8. Let newExtension be a Unicode BCP 47 U Extension based on attributes and keywords.
  9. If newExtension is not the empty String, then
    1. Let locale be ! InsertUnicodeExtensionAndCanonicalize(locale, newExtension).
  10. Set result.[[locale]] to locale.
  11. Return result.

10.1.3 Intl.Locale( tag [, options] )

The following algorithm refers to UTS 35's Unicode Language and Locale Identifiers grammar. 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 relevantExtensionKeys be %Locale%.[[RelevantExtensionKeys]].
  3. Let internalSlotsList be « [[InitializedLocale]], [[Locale]], [[Calendar]], [[Collation]], [[HourCycle]], [[NumberingSystem]] ».
  4. If relevantExtensionKeys contains "kf", then
    1. Append [[CaseFirst]] as the last element of internalSlotsList.
  5. If relevantExtensionKeys contains "kn", then
    1. Append [[Numeric]] as the last element of internalSlotsList.
  6. Let locale be ? OrdinaryCreateFromConstructor(NewTarget, %LocalePrototype%, internalSlotsList).
  7. If Type(tag) is not String or Object, throw a TypeError exception.
  8. If Type(tag) is Object and tag has an [[InitializedLocale]] internal slot, then
    1. Let tag be tag.[[Locale]].
  9. Else,
    1. Let tag be ? ToString(tag).
  10. If options is undefined, then
    1. Let options be ! ObjectCreate(null).
  11. Else
    1. Let options be ? ToObject(options).
  12. Set tag to ? ApplyOptionsToTag(tag, options).
  13. Let opt be a new Record.
  14. Let calendar be ? GetOption(options, "calendar", "string", undefined, undefined).
  15. If calendar is not undefined, then
    1. If calendar does not match the type sequence (from UTS 35 Unicode Locale Identifier, section 3.2), throw a RangeError exception.
  16. Set opt.[[ca]] to calendar.
  17. Let collation be ? GetOption(options, "collation", "string", undefined, undefined).
  18. If collation is not undefined, then
    1. If collation does not match the type sequence (from UTS 35 Unicode Locale Identifier, section 3.2), throw a RangeError exception.
  19. Set opt.[[co]] to collation.
  20. Let hc be ? GetOption(options, "hourCycle", "string", « "h11", "h12", "h23", "h24" », undefined).
  21. Set opt.[[hc]] to hc.
  22. Let kf be ? GetOption(options, "caseFirst", "string", « "upper", "lower", "false" », undefined).
  23. Set opt.[[kf]] to kf.
  24. Let kn be ? GetOption(options, "numeric", "boolean", undefined, undefined).
  25. If kn is not undefined, set kn to ! ToString(kn).
  26. Set opt.[[kn]] to kn.
  27. Let numberingSystem be ? GetOption(options, "numberingSystem", "string", undefined, undefined).
  28. If numberingSystem is not undefined, then
    1. If numberingSystem does not match the type sequence (from UTS 35 Unicode Locale Identifier, section 3.2), throw a RangeError exception.
  29. Set opt.[[nu]] to numberingSystem.
  30. Let r be ! ApplyUnicodeExtensionToTag(tag, opt, relevantExtensionKeys).
  31. Set locale.[[Locale]] to r.[[locale]].
  32. Set locale.[[Calendar]] to r.[[ca]].
  33. Set locale.[[Collation]] to r.[[co]].
  34. Set locale.[[HourCycle]] to r.[[hc]].
  35. If relevantExtensionKeys contains "kf", then
    1. Set locale.[[CaseFirst]] to r.[[kf]].
  36. If relevantExtensionKeys contains "kn", then
    1. If ! SameValue(r.[[kn]], "true") is true or ! SameValue(r.[[kn]], "") is true, then
      1. Let numeric be true.
    2. Else,
      1. Let numeric be false.
    3. Set locale.[[Numeric]] to numeric.
  37. Set locale.[[NumberingSystem]] to r.[[nu]].
  38. Return locale.

10.2 Properties of the Intl.Locale Constructor

The Intl.Locale constructor has the following properties:

10.2.1 Intl.Locale.prototype

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

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

10.2.2 Internal slots

The value of the [[RelevantExtensionKeys]] internal slot is « "ca", "co", "hc", "kf", "kn", "nu" ». If %Collator%.[[RelevantExtensionKeys]] does not contain "kf", then remove "kf" from %Locale%.[[RelevantExtensionKeys]]. If %Collator%.[[RelevantExtensionKeys]] does not contain "kn", then remove "kn" from %Locale%.[[RelevantExtensionKeys]].

10.3 Properties of the Intl.Locale Prototype Object

The Intl.Locale prototype object is itself an ordinary object. %LocalePrototype% 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.

10.3.1 Intl.Locale.prototype.constructor

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

10.3.2 Intl.Locale.prototype[ @@toStringTag ]

The initial value of the @@toStringTag property is the string value "Intl.Locale".

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

10.3.3 Intl.Locale.prototype.maximize ()

  1. Let loc be the this value.
  2. Perform ? RequireInternalSlot(loc, [[InitializedLocale]]).
  3. Let maximal be the result of the Add Likely Subtags algorithm applied to loc.[[Locale]]. If an error is signaled, set maximal to loc.[[Locale]].
  4. Return ! Construct(%Locale%, maximal).

10.3.4 Intl.Locale.prototype.minimize ()

  1. Let loc be the this value.
  2. Perform ? RequireInternalSlot(loc, [[InitializedLocale]]).
  3. Let minimal be the result of the Remove Likely Subtags algorithm applied to loc.[[Locale]]. If an error is signaled, set minimal to loc.[[Locale]].
  4. Return ! Construct(%Locale%, minimal).

10.3.5 Intl.Locale.prototype.toString ()

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

10.3.6 get Intl.Locale.prototype.baseName

Intl.Locale.prototype.baseName is an accessor property whose set accessor function is undefined. The following algorithm refers to UTS 35's Unicode Language and Locale Identifiers grammar. Its get accessor function performs the following steps:

  1. Let loc be the this value.
  2. Perform ? RequireInternalSlot(loc, [[InitializedLocale]]).
  3. Let locale be loc.[[Locale]].
  4. Return the substring of locale corresponding to the unicode_language_id production.

10.3.7 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]].

10.3.8 get Intl.Locale.prototype.caseFirst

This property only exists if %Locale%.[[RelevantExtensionKeys]] 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]].

10.3.9 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]].

10.3.10 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]].

10.3.11 get Intl.Locale.prototype.numeric

This property only exists if %Locale%.[[RelevantExtensionKeys]] 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]].

10.3.12 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]].

10.3.13 get Intl.Locale.prototype.language

Intl.Locale.prototype.language is an accessor property whose set accessor function is undefined. The following algorithm refers to UTS 35's Unicode Language and Locale Identifiers grammar. Its get accessor function performs the following steps:

  1. Let loc be the this value.
  2. Perform ? RequireInternalSlot(loc, [[InitializedLocale]]).
  3. Let locale be loc.[[Locale]].
  4. Assert: locale matches the unicode_locale_id production.
  5. Return the substring of locale corresponding to the unicode_language_subtag production of the unicode_language_id.

10.3.14 get Intl.Locale.prototype.script

Intl.Locale.prototype.script is an accessor property whose set accessor function is undefined. The following algorithm refers to UTS 35's Unicode Language and Locale Identifiers grammar. Its get accessor function performs the following steps:

  1. Let loc be the this value.
  2. Perform ? RequireInternalSlot(loc, [[InitializedLocale]]).
  3. Let locale be loc.[[Locale]].
  4. Assert: locale matches the unicode_locale_id production.
  5. If the unicode_language_id production of locale does not contain the ["-" unicode_script_subtag] sequence, return undefined.
  6. Return the substring of locale corresponding to the unicode_script_subtag production of the unicode_language_id.

10.3.15 get Intl.Locale.prototype.region

Intl.Locale.prototype.region is an accessor property whose set accessor function is undefined. The following algorithm refers to UTS 35's Unicode Language and Locale Identifiers grammar. Its get accessor function performs the following steps:

  1. Let loc be the this value.
  2. Perform ? RequireInternalSlot(loc, [[InitializedLocale]]).
  3. Let locale be loc.[[Locale]].
  4. Assert: locale matches the unicode_locale_id production.
  5. If the unicode_language_id production of locale does not contain the ["-" unicode_region_subtag] sequence, return undefined.
  6. Return the substring of locale corresponding to the unicode_region_subtag production of the unicode_language_id.

11 Collator Objects

11.1 The Intl.Collator Constructor

The Intl.Collator constructor is the %Collator% intrinsic object and a standard built-in property of the Intl object. Behaviour common to all service constructor properties of the Intl object is specified in 9.1.

11.1.1 InitializeCollator ( collator, locales, options )

The abstract operation InitializeCollator accepts the arguments collator (which must be an object), locales, and options. It initializes collator as a Collator object. The following steps are taken:

  1. Let requestedLocales be ? CanonicalizeLocaleList(locales).
  2. If options is undefined, then
    1. Let options be ObjectCreate(null).
  3. Else,
    1. Let options be ? ToObject(options).
  4. Let usage be ? GetOption(options, "usage", "string", « "sort", "search" », "sort").
  5. Set collator.[[Usage]] to usage.
  6. If usage is "sort", then
    1. Let localeData be %Collator%.[[SortLocaleData]].
  7. Else,
    1. Let localeData be %Collator%.[[SearchLocaleData]].
  8. Let opt be a new Record.
  9. Let matcher be ? GetOption(options, "localeMatcher", "string", « "lookup", "best fit" », "best fit").
  10. Set opt.[[localeMatcher]] to matcher.
  11. Let numeric be ? GetOption(options, "numeric", "boolean", undefined, undefined).
  12. If numeric is not undefined, then
    1. Let numeric be ! ToString(numeric).
  13. Set opt.[[kn]] to numeric.
  14. Let caseFirst be ? GetOption(options, "caseFirst", "string", « "upper", "lower", "false" », undefined).
  15. Set opt.[[kf]] to caseFirst.
  16. Let relevantExtensionKeys be %Collator%.[[RelevantExtensionKeys]].
  17. Let r be ResolveLocale(%Collator%.[[AvailableLocales]], requestedLocales, opt, relevantExtensionKeys, localeData).
  18. Set collator.[[Locale]] to r.[[locale]].
  19. Let collation be r.[[co]].
  20. If collation is null, let collation be "default".
  21. Set collator.[[Collation]] to collation.
  22. If relevantExtensionKeys contains "kn", then
    1. Set collator.[[Numeric]] to ! SameValue(r.[[kn]], "true").
  23. If relevantExtensionKeys contains "kf", then
    1. Set collator.[[CaseFirst]] to r.[[kf]].
  24. Let sensitivity be ? GetOption(options, "sensitivity", "string", « "base", "accent", "case", "variant" », undefined).
  25. If sensitivity is undefined, then
    1. If usage is "sort", then
      1. Let sensitivity be "variant".
    2. Else,
      1. Let dataLocale be r.[[dataLocale]].
      2. Let dataLocaleData be localeData.[[<dataLocale>]].
      3. Let sensitivity be dataLocaleData.[[sensitivity]].
  26. Set collator.[[Sensitivity]] to sensitivity.
  27. Let ignorePunctuation be ? GetOption(options, "ignorePunctuation", "boolean", undefined, false).
  28. Set collator.[[IgnorePunctuation]] to ignorePunctuation.
  29. Return collator.

11.1.2 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 active function object, else let newTarget be NewTarget.
  2. Let internalSlotsList be « [[InitializedCollator]], [[Locale]], [[Usage]], [[Sensitivity]], [[IgnorePunctuation]], [[Collation]], [[BoundCompare]] ».
  3. If %Collator%.[[RelevantExtensionKeys]] contains "kn", then
    1. Append [[Numeric]] as the last element of internalSlotsList.
  4. If %Collator%.[[RelevantExtensionKeys]] contains "kf", then
    1. Append [[CaseFirst]] as the last element of internalSlotsList.
  5. Let collator be ? OrdinaryCreateFromConstructor(newTarget, "%CollatorPrototype%", internalSlotsList).
  6. Return ? InitializeCollator(collator, locales, options).

11.2 Properties of the Intl.Collator Constructor

The Intl.Collator constructor has the following properties:

11.2.1 Intl.Collator.prototype

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

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

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

The value of the "length" property of the supportedLocalesOf method is 1.

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 a List that must include the element "co", may include any or all of the elements "kn" and "kf", and must not include any other elements.

Note
Unicode Technical Standard 35 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, "kn" for numeric, "kh" for hiragana quaternary, "kk" for normalization, "kf" for case first, "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 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 a String value equal to "base", "accent", "case", or "variant".

11.3 Properties of the Intl.Collator Prototype Object

The Intl.Collator prototype object is itself an ordinary object. %CollatorPrototype% 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.

11.3.1 Intl.Collator.prototype.constructor

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

11.3.2 Intl.Collator.prototype [ @@toStringTag ]

The initial value of the @@toStringTag property is the String value "Object".

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

11.3.3 get Intl.Collator.prototype.compare

This named accessor property returns a function that compares two strings according to the 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 this value.
  2. Perform ? RequireInternalSlot(collator, [[InitializedCollator]]).
  3. If collator.[[BoundCompare]] is undefined, then
    1. Let F be a new built-in function object as defined in 11.3.3.1.
    2. Set F.[[Collator]] to collator.
    3. Set collator.[[BoundCompare]] to F.
  4. 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.

11.3.3.1 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. Assert: Type(collator) is Object and collator has an [[InitializedCollator]] internal slot.
  3. If x is not provided, let x be undefined.
  4. If y is not provided, let y be undefined.
  5. Let X be ? ToString(x).
  6. Let Y be ? ToString(y).
  7. Return CompareStrings(collator, X, Y).

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

11.3.3.2 CompareStrings ( collator, x, y )

When the CompareStrings abstract operation is called with arguments collator (which must be an object initialized as a Collator), x and y (which must be String values), it returns a Number other than NaN that represents the result of a locale-sensitive String comparison of x with y. The two Strings are compared in an implementation-defined fashion. The result is intended to order String values in the sort order specified by the effective locale and collation options computed during construction of collator, and will be negative, zero, or positive, depending on whether x comes before y in the sort order, the Strings are equal under the sort order, or x comes after y in the sort order, respectively. String values must be interpreted as UTF-16 code unit sequences, and a 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.

The sensitivity of collator is interpreted as follows:

  • base: Only strings that differ in base letters compare as unequal. Examples: a ≠ b, a = á, a = A.
  • accent: Only strings that differ in base letters or accents and other diacritic marks compare as unequal. Examples: a ≠ b, a ≠ á, a = A.
  • case: Only strings that differ in base letters or case compare as unequal. Examples: a ≠ b, a = á, a ≠ A.
  • variant: Strings that differ in base letters, accents and other diacritic marks, or case compare as unequal. Other differences may also be taken into consideration. Examples: a ≠ b, a ≠ á, a ≠ A.
Note 1
In some languages, certain letters with diacritic marks are considered base letters. For example, in Swedish, "ö" is a base letter that's different from "o".

If the collator is set to ignore punctuation, then strings that differ only in punctuation compare as equal.

For the interpretation of options settable through extension keys, see Unicode Technical Standard 35.

The CompareStrings abstract operation with any given collator argument, if considered as a function of the remaining two arguments x and y, must be a consistent comparison function (as defined in ES2020, 22.1.3.27) on the set of all Strings.

The actual return values are implementation-defined to permit implementers to encode additional information in the value. The method is required to return +0 when comparing Strings that are considered canonically equivalent by the Unicode standard.

Note 2
It is recommended that the CompareStrings abstract operation be implemented following Unicode Technical Standard 10, Unicode Collation Algorithm (available at https://unicode.org/reports/tr10/), 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 http://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.

11.3.4 Intl.Collator.prototype.resolvedOptions ()

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

  1. Let collator be this value.
  2. Perform ? RequireInternalSlot(collator, [[InitializedCollator]]).
  3. Let options be ! ObjectCreate(%ObjectPrototype%).
  4. For each row of Table 3, 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 collator's internal slot whose name is the Internal Slot value of the current row.
    3. If the current row has an Extension Key value, then
      1. Let extensionKey be the Extension Key value of the current row.
      2. If %Collator%.[[RelevantExtensionKeys]] does not contain extensionKey, then
        1. Let v be undefined.
    4. If v is not undefined, then
      1. Perform ! CreateDataPropertyOrThrow(options, p, v).
  5. 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"

11.4 Properties of Intl.Collator Instances

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

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

Intl.Collator instances also have several internal slots that are computed by the 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]] is a String value with the "type" given in Unicode Technical Standard 35 for the 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 (11.3.3).

12 NumberFormat Objects

12.1 Abstract Operations For NumberFormat Objects

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

The abstract operation SetNumberFormatDigitOptions applies digit options used for number formatting onto the intl object.

  1. Assert: Type(intlObj) is Object.
  2. Assert: Type(options) is Object.
  3. Assert: Type(mnfdDefault) is Number.
  4. Assert: Type(mxfdDefault) is Number.
  5. Let mnid be ? GetNumberOption(options, "minimumIntegerDigits,", 1, 21, 1).
  6. Let mnfd be ? Get(options, "minimumFractionDigits").
  7. Let mxfd be ? Get(options, "maximumFractionDigits").
  8. Let mnsd be ? Get(options, "minimumSignificantDigits").
  9. Let mxsd be ? Get(options, "maximumSignificantDigits").
  10. Set intlObj.[[MinimumIntegerDigits]] to mnid.
  11. If mnsd is not undefined or mxsd is not undefined, then
    1. Set intlObj.[[RoundingType]] to significantDigits.
    2. Let mnsd be ? DefaultNumberOption(mnsd, 1, 21, 1).
    3. Let mxsd be ? DefaultNumberOption(mxsd, mnsd, 21, 21).
    4. Set intlObj.[[MinimumSignificantDigits]] to mnsd.
    5. Set intlObj.[[MaximumSignificantDigits]] to mxsd.
  12. Else if mnfd is not undefined or mxfd is not undefined, then
    1. Set intlObj.[[RoundingType]] to fractionDigits.
    2. Let mnfd be ? DefaultNumberOption(mnfd, 0, 20, mnfdDefault).
    3. Let mxfdActualDefault be max( mnfd, mxfdDefault ).
    4. Let mxfd be ? DefaultNumberOption(mxfd, mnfd, 20, mxfdActualDefault).
    5. Set intlObj.[[MinimumFractionDigits]] to mnfd.
    6. Set intlObj.[[MaximumFractionDigits]] to mxfd.
  13. Else if notation is "compact", then
    1. Set intlObj.[[RoundingType]] to compactRounding.
  14. Else,
    1. Set intlObj.[[RoundingType]] to fractionDigits.
    2. Set intlObj.[[MinimumFractionDigits]] to mnfdDefault.
    3. Set intlObj.[[MaximumFractionDigits]] to mxfdDefault.

12.1.2 InitializeNumberFormat ( numberFormat, locales, options )

The abstract operation InitializeNumberFormat accepts the arguments numberFormat (which must be an object), locales, and options. It initializes numberFormat as a NumberFormat object. The following steps are taken:

The following algorithm refers to the type nonterminal from UTS 35's Unicode Locale Identifier grammar.

  1. Let requestedLocales be ? CanonicalizeLocaleList(locales).
  2. If options is undefined, then
    1. Let options be ObjectCreate(null).
  3. Else,
    1. Let options be ? ToObject(options).
  4. Let opt be a new Record.
  5. Let matcher be ? GetOption(options, "localeMatcher", "string", « "lookup", "best fit" », "best fit").
  6. Set opt.[[localeMatcher]] to matcher.
  7. Let numberingSystem be ? GetOption(options, "numberingSystem", "string", undefined, undefined).
  8. If numberingSystem is not undefined, then
    1. If numberingSystem does not match the Unicode Locale Identifier type nonterminal, throw a RangeError exception.
  9. Set opt.[[nu]] to numberingSystem.
  10. Let localeData be %NumberFormat%.[[LocaleData]].
  11. Let r be ResolveLocale(%NumberFormat%.[[AvailableLocales]], requestedLocales, opt, %NumberFormat%.[[RelevantExtensionKeys]], localeData).
  12. Set numberFormat.[[Locale]] to r.[[locale]].
  13. Set numberFormat.[[DataLocale]] to r.[[dataLocale]].
  14. Set numberFormat.[[NumberingSystem]] to r.[[nu]].
  15. Perform ? SetNumberFormatUnitOptions(numberFormat, options).
  16. Let style be numberFormat.[[Style]].
  17. If style is "currency", then
    1. Let currency be numberFormat.[[Currency]].
    2. Let cDigits be CurrencyDigits(currency).
    3. Let mnfdDefault be cDigits.
    4. Let mxfdDefault be cDigits.
  18. Else,
    1. Let mnfdDefault be 0.
    2. If style is "percent", then
      1. Let mxfdDefault be 0.
    3. Else,
      1. Let mxfdDefault be 3.
  19. Let notation be ? GetOption(options, "notation", "string", « "standard", "scientific", "engineering", "compact" », "standard").
  20. Set numberFormat.[[Notation]] to notation.
  21. Perform ? SetNumberFormatDigitOptions(numberFormat, options, mnfdDefault, mxfdDefault, notation).
  22. Let compactDisplay be ? GetOption(options, "compactDisplay", "string", « "short", "long" », "short").
  23. If notation is "compact", then
    1. Set numberFormat.[[CompactDisplay]] to compactDisplay.
  24. Let useGrouping be ? GetOption(options, "useGrouping", "boolean", undefined, true).
  25. Set numberFormat.[[UseGrouping]] to useGrouping.
  26. Let signDisplay be ? GetOption(options, "signDisplay", "string", « "auto", "never", "always", "exceptZero" », "auto").
  27. Set numberFormat.[[SignDisplay]] to signDisplay.
  28. Return numberFormat.

12.1.3 CurrencyDigits ( currency )

When the CurrencyDigits abstract operation is called with an argument currency (which must be an upper case String value), the following steps are taken:

  1. If the ISO 4217 currency and funds code list contains currency as an alphabetic code, return the minor unit value corresponding to the currency from the list; otherwise, return 2.

12.1.4 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. Assert: Type(nf) is Object and nf has an [[InitializedNumberFormat]] internal slot.
  3. If value is not provided, let value be undefined.
  4. Let x be ? ToNumeric(value).
  5. Return ? FormatNumeric(nf, x).

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

12.1.5 FormatNumericToString ( intlObject, x )

The FormatNumericToString abstract operation is called with arguments intlObject (which must be an object with [[RoundingType]], [[MinimumSignificantDigits]], [[MaximumSignificantDigits]], [[MinimumIntegerDigits]], [[MinimumFractionDigits]], and [[MaximumFractionDigits]] internal slots), and x (which must be a Number or BigInt value), and returns a Record containing two values: x as a String value with digits formatted according to the five formatting parameters in the field [[FormattedString]], and the final floating decimal value of x after rounding has been performed in the field [[RoundedNumber]].

  1. If x < 0 or x is -0, let isNegative be true; else let isNegative be false.
  2. If isNegative, then
    1. Let x be -x.
  3. If intlObject.[[RoundingType]] is significantDigits, then
    1. Let result be ToRawPrecision(x, intlObject.[[MinimumSignificantDigits]], intlObject.[[MaximumSignificantDigits]]).
  4. Else if intlObject.[[RoundingType]] is fractionDigits, then
    1. Let result be ToRawFixed(x, intlObject.[[MinimumFractionDigits]], intlObject.[[MaximumFractionDigits]]).
  5. Else,
    1. Assert: intlObject.[[RoundingType]] is compactRounding.
    2. Let result be ToRawPrecision(x, 1, 2).
    3. If result.[[IntegerDigitsCount]] > 1, then
      1. Let result be ToRawFixed(x, 0, 0).
  6. Let x be result.[[RoundedNumber]].
  7. Let string be result.[[FormattedString]].
  8. Let int be result.[[IntegerDigitsCount]].
  9. Let minInteger be intlObject.[[MinimumIntegerDigits]].
  10. If int < minInteger, then
    1. Let forwardZeros be the String consisting of minInteger–int occurrences of the character "0".
    2. Set string to the string-concatenation of forwardZeros and string.
  11. If isNegative, then
    1. Let x be -x.
  12. Return the Record { [[RoundedNumber]]: x, [[FormattedString]]: string }.

12.1.6 PartitionNumberPattern ( numberFormat, x )

The PartitionNumberPattern abstract operation is called with arguments numberFormat (which must be an object initialized as a NumberFormat) and x (which must be a Number or BigInt value), interprets x as a numeric value, and creates the corresponding parts according to the effective locale and the formatting options of numberFormat. The following steps are taken:

  1. Let exponent be 0.
  2. If x is NaN, then
    1. Let n be an implementation- and locale-dependent (ILD) String value indicating the NaN value.
  3. Else if x is a non-finite Number, then
    1. Let n be an ILD String value indicating infinity.
  4. Else,
    1. If numberFormat.[[Style]] is "percent", let x be 100 × x.
    2. Let exponent be ComputeExponent(numberFormat, x).
    3. Let x be x × 10-exponent.
    4. Let formatNumberResult be FormatNumericToString(numberFormat, x).
    5. Let n be formatNumberResult.[[FormattedString]].
    6. Let x be formatNumberResult.[[RoundedNumber]].
  5. Let pattern be GetNumberFormatPattern(numberFormat, x)
  6. Let result be a new empty List.
  7. Let patternParts be PartitionPattern(pattern).
  8. For each element patternPart of patternParts, in List order, do
    1. Let p be patternPart.[[Type]].
    2. If p is "literal", then
      1. Append a new Record { [[Type]]: "literal", [[Value]]: patternPart.[[Value]] } as the last element of result.
    3. Else if p is equal to "number", then
      1. Let notationSubParts be PartitionNotationSubPattern(numberFormat, x, n, exponent).
      2. Append all elements of notationSubParts to result.
    4. Else if p is equal to "plusSign", then
      1. Let plusSignSymbol be the ILND String representing the plus sign.
      2. Append a new Record { [[Type]]: "plusSign", [[Value]]: plusSignSymbol } as the last element of result.
    5. Else if p is equal to "minusSign", then
      1. Let minusSignSymbol be the ILND String representing the minus sign.
      2. Append a new Record { [[Type]]: "minusSign", [[Value]]: minusSignSymbol } as the last element of result.
    6. Else if p is equal to "percentSign" and numberFormat.[[Style]] is "percent", then
      1. Let percentSignSymbol be the ILND String representing the percent sign.
      2. Append a new Record { [[Type]]: "percentSign", [[Value]]: percentSignSymbol } as the last element of result.
    7. Else if p is equal to "unitPrefix" and numberFormat.[[Style]] is "unit", then
      1. Let unit be numberFormat.[[Unit]].
      2. Let unitDisplay be numberFormat.[[UnitDisplay]].
      3. Let mu be an ILD String value representing unit before x in unitDisplay form, which may depend on x in languages having different plural forms.
      4. Append a new Record { [[Type]]: "unit", [[Value]]: mu } as the last element of result.
    8. Else if p is equal to "unitSuffix" and numberFormat.[[Style]] is "unit", then
      1. Let unit be numberFormat.[[Unit]].
      2. Let unitDisplay be numberFormat.[[UnitDisplay]].
      3. Let mu be an ILD String value representing unit after x in unitDisplay form, which may depend on x in languages having different plural forms.
      4. Append a new Record { [[Type]]: "unit", [[Value]]: mu } as the last element of result.
    9. Else if p is equal to "currencyCode" and numberFormat.[[Style]] is "currency", then
      1. Let currency be numberFormat.[[Currency]].
      2. Let cd be currency.
      3. Append a new Record { [[Type]]: "currency", [[Value]]: cd } as the last element of result.
    10. Else if p is equal to "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 a new Record { [[Type]]: "currency", [[Value]]: cd } as the last element of result.
    11. Else if p is equal to "currencySuffix" 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 after x in currencyDisplay form, which may depend on x in languages having different plural forms. If the implementation does not have such a representation of currency, use currency itself.
      4. Append a new Record { [[Type]]: "currency", [[Value]]: cd } as the last element of result.
    12. Else,
      1. Let unknown be an ILND String based on x and p.
      2. Append a new Record { [[Type]]: "unknown", [[Value]]: unknown } as the last element of result.
  9. Return result.

12.1.7 PartitionNotationSubPattern ( numberFormat, x, n, exponent )

The PartitionNotationSubPattern abstract operation is called with arguments numberFormat (which must be an object initialized as a NumberFormat), x (which is a numeric value after rounding is applied), n (which is an intermediate formatted string), and exponent (an integer), and creates the corresponding parts for the number and notation according to the effective locale and the formatting options of numberFormat. The following steps are taken:

  1. Let result be a new empty List.
  2. If x is NaN, then
    1. Append a new Record { [[Type]]: "nan", [[Value]]: n } as the last element of result.
  3. Else if x is a non-finite Number, then
    1. Append a new Record { [[Type]]: "infinity", [[Value]]: n } as the last element of result.
  4. Else,
    1. Let notationSubPattern be GetNotationSubPattern(numberFormat, exponent)
    2. Let patternParts be PartitionPattern(notationSubPattern).
    3. For each element patternPart of patternParts, in List order, do
      1. Let p be patternPart.[[Type]].
      2. If p is "literal", then
        1. Append a new Record { [[Type]]: "literal", [[Value]]: patternPart.[[Value]] } as the last element of result.
      3. Else if p is equal to "number", then
        1. If the numberFormat.[[NumberingSystem]] matches one of the values in the "Numbering System" column of Table 4 below, then
          1. Let digits be a List whose 10 String valued elements are the UTF-16 string representations of the 10 digits specified in the "Digits" column of the matching row in Table 4.
          2. Replace each digit in n with the value of digits[digit].
        2. Else use an implementation dependent algorithm to map n to the appropriate representation of n in the given numbering system.
        3. Let decimalSepIndex be Call(%StringProto_indexOf%, n, « ".", 0 »).
        4. If decimalSepIndex > 0, then
          1. Let integer be the substring of n from position 0, inclusive, to position decimalSepIndex, exclusive.
          2. Let fraction be the substring of n from position decimalSepIndex, exclusive, to the end of n.
        5. Else,
          1. Let integer be n.
          2. Let fraction be undefined.
        6. If the numberFormat.[[UseGrouping]] is true, then
          1. Let groupSepSymbol be the implementation-, locale-, and numbering system-dependent (ILND) String representing the grouping separator.
          2. Let groups be a List whose elements are, in left to right order, the substrings defined by ILND set of locations within the integer.
          3. Assert: The number of elements in groups List is greater than 0.
          4. Repeat, while groups List is not empty
            1. Remove the first element from groups and let integerGroup be the value of that element.
            2. Append a new Record { [[Type]]: "integer", [[Value]]: integerGroup } as the last element of result.
            3. If groups List is not empty, then
              1. Append a new Record { [[Type]]: "group", [[Value]]: groupSepSymbol } as the last element of result.
        7. Else,
          1. Append a new Record { [[Type]]: "integer", [[Value]]: integer } as the last element of result.
        8. If fraction is not undefined, then
          1. Let decimalSepSymbol be the ILND String representing the decimal separator.
          2. Append a new Record { [[Type]]: "decimal", [[Value]]: decimalSepSymbol } as the last element of result.
          3. Append a new Record { [[Type]]: "fraction", [[Value]]: fraction } as the last element of result.
      4. Else if p is equal to "compactSymbol", then
        1. Let compactSymbol be an ILD string representing exponent in short form, which may depend on x in languages having different plural forms. The implementation must be able to provide this string, or else the pattern would not have a "{compactSymbol}" placeholder.
        2. Append a new Record { [[Type]]: "compact", [[Value]]: compactSymbol } as the last element of result.
      5. Else if p is equal to "compactName", then
        1. Let compactName be an ILD string representing exponent in long form, which may depend on x in languages having different plural forms. The implementation must be able to provide this string, or else the pattern would not have a "{compactName}" placeholder.
        2. Append a new Record { [[Type]]: "compact", [[Value]]: compactName } as the last element of result.
      6. Else if p is equal to "scientificSeparator", then
        1. Let scientificSeparator be the ILND String representing the exponent separator.
        2. Append a new Record { [[Type]]: "exponentSeparator", [[Value]]: scientificSeparator } as the last element of result.
      7. Else if p is equal to "scientificExponent", then
        1. If exponent < 0, then
          1. Let minusSignSymbol be the ILND String representing the minus sign.
          2. Append a new Record { [[Type]]: "exponentMinusSign", [[Value]]: minusSignSymbol } as the last element of result.
          3. Let exponent be -exponent.
        2. Let exponentResult be ToRawFixed(exponent, 1, 0, 0).
        3. Append a new Record { [[Type]]: "exponentInteger", [[Value]]: exponentResult.[[FormattedString]] } as the last element of result.
      8. Else,
        1. Let unknown be an ILND String based on x and p.
        2. Append a new Record { [[Type]]: "unknown", [[Value]]: unknown } as the last element of result.
  5. Return result.
Table 4: Numbering systems with simple digit mappings
Numbering System Digits
arab U+0660 to U+0669
arabext U+06F0 to U+06F9
bali U+1B50 to U+1B59
beng U+09E6 to U+09EF
deva U+0966 to U+096F
fullwide U+FF10 to U+FF19
gujr U+0AE6 to U+0AEF
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
khmr U+17E0 to U+17E9
knda U+0CE6 to U+0CEF
laoo U+0ED0 to U+0ED9
latn U+0030 to U+0039
limb U+1946 to U+194F
mlym U+0D66 to U+0D6F
mong U+1810 to U+1819
mymr U+1040 to U+1049
orya U+0B66 to U+0B6F
tamldec U+0BE6 to U+0BEF
telu U+0C66 to U+0C6F
thai U+0E50 to U+0E59
tibt U+0F20 to U+0F29
Note 1
The computations rely on String values and locations within numeric strings that are dependent upon the implementation and the effective locale of numberFormat ("ILD") or upon the implementation, the effective locale, and the numbering system of numberFormat ("ILND"). The ILD and ILND Strings mentioned, other than those for currency names, must not contain any characters 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 http://cldr.unicode.org).

12.1.8 FormatNumeric( numberFormat, x )

The FormatNumeric abstract operation is called with arguments numberFormat (which must be an object initialized as a NumberFormat) and x (which must be a Number or BigInt value), and performs the following steps:

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

12.1.9 FormatNumericToParts( numberFormat, x )

The FormatNumericToParts abstract operation is called with arguments numberFormat (which must be an object initialized as a NumberFormat) and x (which must be a Number or BigInt value), and performs the following steps:

  1. Let parts be ? PartitionNumberPattern(numberFormat, x).
  2. Let result be ArrayCreate(0).
  3. Let n be 0.
  4. For each part in parts, do
    1. Let O be ObjectCreate(%ObjectPrototype%).
    2. Perform ! CreateDataPropertyOrThrow(O, "type", part.[[Type]]).
    3. Perform ! CreateDataPropertyOrThrow(O, "value", part.[[Value]]).
    4. Perform ! CreateDataPropertyOrThrow(result, ! ToString(n), O).
    5. Increment n by 1.
  5. Return result.

12.1.10 ToRawPrecision( x, minPrecision, maxPrecision )

When the ToRawPrecision abstract operation is called with arguments x (which must be a finite non-negative Number or BigInt), minPrecision, and maxPrecision (both must be integers between 1 and 21), the following steps are taken:

  1. Let p be maxPrecision.
  2. If x = 0, then
    1. Let m be the String consisting of p occurrences of the character "0".
    2. Let e be 0.
    3. Let xFinal be 0.
  3. Else,
    1. Let e be the base 10 logarithm of x rounded down to the nearest integer.
    2. Let n be an integer such that 10p–1 ≤ n < 10p and for which the exact mathematical value of n × 10e–p+1 – x is as close to zero as possible. If there is more than one such n, pick the one for which n × 10e–p+1 is larger.
    3. Let m be the String consisting of the digits of the decimal representation of n (in order, with no leading zeroes).
    4. Let xFinal be n × 10e–p+1.
  4. If e ≥ p–1, then
    1. Let m be the string-concatenation of m and e–p+1 occurrences of the character "0".
    2. Let int be e+1.
  5. Else if e ≥ 0, then
    1. Let m be the string-concatenation of the first e+1 characters of m, the character ".", and the remaining p–(e+1) characters of m.
    2. Let int be e+1.
  6. Else,
    1. Assert: e < 0.
    2. Let m be the string-concatenation of the String value "0.", –(e+1) occurrences of the character "0", and m.
    3. Let int be 1.
  7. If m contains the character ".", and maxPrecision > minPrecision, then
    1. Let cut be maxPrecision – minPrecision.
    2. Repeat, while cut > 0 and the last character of m is "0"
      1. Remove the last character from m.
      2. Decrease cut by 1.
    3. If the last character of m is ".", then
      1. Remove the last character from m.
  8. Return the Record { [[FormattedString]]: m, [[RoundedNumber]]: xFinal, [[IntegerDigitsCount]]: int }.

12.1.11 ToRawFixed( x, minInteger, minFraction, maxFraction )

When the ToRawFixed abstract operation is called with arguments x (which must be a finite non-negative Number or BigInt), minInteger (which must be an integer between 1 and 21), minFraction, and maxFraction (which must be integers between 0 and 20), the following steps are taken:

  1. Let f be maxFraction.
  2. Let n be an integer for which the exact mathematical value of n ÷ 10f – x is as close to zero as possible. If there are two such n, pick the larger n.
  3. Let xFinal be n ÷ 10f.
  4. If n = 0, let m be the String "0". Otherwise, let m be the String consisting of the digits of the decimal representation of n (in order, with no leading zeroes).
  5. If f ≠ 0, then
    1. Let k be the number of characters in m.
    2. If k ≤ f, then
      1. Let z be the String value consisting of f+1–k occurrences of the character "0".
      2. Let m be the string-concatenation of z and m.
      3. Let k be f+1.
    3. Let a be the first k–f characters of m, and let b be the remaining f characters of m.
    4. Let m be the string-concatenation of a, ".", and b.
    5. Let int be the number of characters in a.
  6. Else, let int be the number of characters in m.
  7. Let cut be maxFraction – minFraction.
  8. Repeat, while cut > 0 and the last character of m is "0"
    1. Remove the last character from m.
    2. Decrease cut by 1.
  9. If the last character of m is ".", then
    1. Remove the last character from m.
  10. Return the Record { [[FormattedString]]: m, [[RoundedNumber]]: xFinal, [[IntegerDigitsCount]]: int }.

12.1.12 UnwrapNumberFormat( nf )

The UnwrapNumberFormat abstract operation gets the underlying NumberFormat operation for various methods which implement ECMA-402 v1 semantics for supporting initializing existing Intl objects.

  1. Assert: Type(nf) is Object.
  1. If nf does not have an [[InitializedNumberFormat]] internal slot and ? InstanceofOperator(nf, %NumberFormat%) is true, then
    1. Let nf be ? Get(nf, %Intl%.[[FallbackSymbol]]).
  1. Perform ? RequireInternalSlot(nf, [[InitializedNumberFormat]]).
  2. Return nf.
Note
See 8.1 Note 1 for the motivation of the normative optional text.

12.1.13 SetNumberFormatUnitOptions ( intlObj, options )

The abstract operation SetNumberFormatUnitOptions resolves the user-specified options relating to units onto the intl object.

  1. Assert: Type(intlObj) is Object.
  2. Assert: Type(options) is Object.
  3. Let style be ? GetOption(options, "style", "string", « "decimal", "percent", "currency", "unit" », "decimal").
  4. Set intlObj.[[Style]] to style.
  5. Let currency be ? GetOption(options, "currency", "string", undefined, undefined).
  6. If currency is not undefined, then
    1. If the result of IsWellFormedCurrencyCode(currency) is false, throw a RangeError exception.
  7. If style is "currency" and currency is undefined, throw a TypeError exception.
  8. Let currencyDisplay be ? GetOption(options, "currencyDisplay", "string", « "code", "symbol", "narrowSymbol", "name" », "symbol").
  9. Let currencySign be ? GetOption(options, "currencySign", "string", « "standard", "accounting" », "standard").
  10. Let unit be ? GetOption(options, "unit", "string", undefined, undefined).
  11. If unit is not undefined, then
    1. If the result of IsWellFormedUnitIdentifier(unit) is false, throw a RangeError exception.
  12. If style is "unit" and unit is undefined, throw a TypeError exception.
  13. Let unitDisplay be ? GetOption(options, "unitDisplay", "string", « "short", "narrow", "long" », "short").
  14. If style is "currency", then
    1. Let currency be the result of converting currency to upper case as specified in 6.1.
    2. Set intlObj.[[Currency]] to currency.
    3. Set intlObj.[[CurrencyDisplay]] to currencyDisplay.
    4. Set intlObj.[[CurrencySign]] to currencySign.
  15. If style is "unit", then
    1. Set intlObj.[[Unit]] to unit.
    2. Set intlObj.[[UnitDisplay]] to unitDisplay.

12.1.14 GetNumberFormatPattern ( numberFormat, x )

The abstract operation GetNumberFormatPattern considers the resolved unit-related options in the number format object along with the final scaled and rounded number being formatted and returns a pattern, a String value as described in 12.3.3.

  1. Let localeData be %NumberFormat%.[[LocaleData]].
  2. Let dataLocale be numberFormat.[[DataLocale]].
  3. Let dataLocaleData be localeData.[[<dataLocale>]].
  4. Let patterns be dataLocaleData.[[patterns]].
  5. Assert: patterns is a Record (see 12.3.3).
  6. Let style be numberFormat.[[Style]].
  7. If style is "percent", then
    1. Let patterns be patterns.[[percent]].
  8. Else if style is "unit", then
    1. Let unit be numberFormat.[[Unit]].
    2. Let unitDisplay be numberFormat.[[UnitDisplay]].
    3. Let patterns be patterns.[[unit]].
    4. If patterns doesn't have a field [[<unit>]], then
      1. Let unit be "fallback".
    5. Let patterns be patterns.[[<unit>]].
    6. Let patterns be patterns.[[<unitDisplay>]].
  9. Else if style is "currency", then
    1. Let currency be numberFormat.[[Currency]].
    2. Let currencyDisplay be numberFormat.[[CurrencyDisplay]].
    3. Let currencySign be numberFormat.[[CurrencySign]].
    4. Let patterns be patterns.[[currency]].
    5. If patterns doesn't have a field [[<currency>]], then
      1. Let currency be "fallback".
    6. Let patterns be patterns.[[<currency>]].
    7. Let patterns be patterns.[[<currencyDisplay>]].
    8. Let patterns be patterns.[[<currencySign>]].
  10. Else,
    1. Assert: style is "decimal".
    2. Let patterns be patterns.[[decimal]].
  11. Let signDisplay be numberFormat.[[SignDisplay]].
  12. If signDisplay is "never", then
    1. Let pattern be patterns.[[zeroPattern]].
  13. Else if signDisplay is "auto", then
    1. If x is 0 or x > 0 or x is NaN, then
      1. Let pattern be patterns.[[zeroPattern]].
    2. Else,
      1. Let pattern be patterns.[[negativePattern]].
  14. Else if signDisplay is "always", then
    1. If x is 0 or x > 0 or x is NaN, then
      1. Let pattern be patterns.[[positivePattern]].
    2. Else,
      1. Let pattern be patterns.[[negativePattern]].
  15. Else,
    1. Assert: signDisplay is "exceptZero".
    2. If x is 0 or x is -0 or x is NaN, then
      1. Let pattern be patterns.[[zeroPattern]].
    3. Else if x > 0, then
      1. Let pattern be patterns.[[positivePattern]].
    4. Else,
      1. Let pattern be patterns.[[negativePattern]].
  16. Return pattern.

12.1.15 GetNotationSubPattern ( numberFormat, exponent )

The abstract operation GetNotationSubPattern considers the resolved notation and exponent, and returns a String value for the notation sub pattern as described in 12.3.3.

  1. Let localeData be %NumberFormat%.[[LocaleData]].
  2. Let dataLocale be numberFormat.[[DataLocale]].
  3. Let dataLocaleData be localeData.[[<dataLocale>]].
  4. Let notationSubPatterns be dataLocaleData.[[notationSubPatterns]].
  5. Assert: notationSubPatterns is a Record (see 12.3.3).
  6. Let notation be numberFormat.[[Notation]].
  7. If notation is "scientific" or notation is "engineering", then
    1. Return notationSubPatterns.[[scientific]].
  8. Else if exponent is not 0, then
    1. Assert: notation is "compact".
    2. Let compactDisplay be numberFormat.[[CompactDisplay]].
    3. Let compactPatterns be notationSubPatterns.[[compact]].[[<compactDisplay>]].
    4. Return compactPatterns.[[<exponent>]].
  9. Else,
    1. Return "{number}".

12.1.16 ComputeExponent ( numberFormat, x )

The abstract operation ComputeExponent 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.

  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. Let exponent be ComputeExponentForMagnitude(numberFormat, magnitude).
  5. Let x be x × 10-exponent.
  6. Let formatNumberResult be FormatNumericToString(numberFormat, x).
  7. If formatNumberResult.[[RoundedNumber]] = 0, then
    1. Return exponent.
  8. Let newMagnitude be the base 10 logarithm of x rounded down to the nearest integer.
  9. If newMagnitude is magnitude – exponent, then
    1. Return exponent.
  10. Return ComputeExponentForMagnitude(numberFormat, magnitude + 1).

12.1.17 ComputeExponentForMagnitude ( numberFormat, magnitude )

The abstract operation ComputeExponentHelper 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).

  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 that is not greater than magnitude ÷ 3.
    2. Return thousands × 3.
  5. Else,
    1. Assert: notation is "compact".
    2. Let exponent be an implementation- and locale-dependent (ILD) integer by which to scale a number of the given magnitude in compact notation for the current locale.
    3. Return exponent.

12.2 The Intl.NumberFormat Constructor

The NumberFormat constructor is the %NumberFormat% intrinsic object and a standard built-in property of the Intl object. Behaviour common to all service constructor properties of the Intl object is specified in 9.1.

12.2.1 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 active function object, else let newTarget be NewTarget.
  2. Let numberFormat be ? OrdinaryCreateFromConstructor(newTarget, "%NumberFormatPrototype%", « [[InitializedNumberFormat]], [[Locale]], [[DataLocale]], [[NumberingSystem]], [[Style]], [[Unit]], [[UnitDisplay]], [[Currency]], [[CurrencyDisplay]], [[CurrencySign]], [[MinimumIntegerDigits]], [[MinimumFractionDigits]], [[MaximumFractionDigits]], [[MinimumSignificantDigits]], [[MaximumSignificantDigits]], [[RoundingType]], [[Notation]], [[CompactDisplay]], [[UseGrouping]], [[SignDisplay]], [[BoundFormat]] »).
  3. Perform ? InitializeNumberFormat(numberFormat, locales, options).
  1. Let this be the this value.
  2. If NewTarget is undefined and Type(this) is Object and ? InstanceofOperator(this, %NumberFormat%) is true, then
    1. Perform ? DefinePropertyOrThrow(this, %Intl%.[[FallbackSymbol]], PropertyDescriptor{ [[Value]]: numberFormat, [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }).
    2. Return this.
  1. Return numberFormat.
Note
See 8.1 Note 1 for the motivation of the normative optional text.

12.3 Properties of the Intl.NumberFormat Constructor

The Intl.NumberFormat constructor has the following properties:

12.3.1 Intl.NumberFormat.prototype

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

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

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

The value of the "length" property of the supportedLocalesOf method is 1.

12.3.3 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" ».

Note 1
Unicode Technical Standard 35 describes two locale extension keys that are relevant to number formatting, "nu" for numbering system and "cu" for currency. Intl.NumberFormat, however, requires that the currency of a currency format is specified through the currency 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 6.5. 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 "{plusSign}" but not "{minusSign}"; "negativePattern" 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 must not contain any characters 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 Record, which must have two fields: [[scientific]] and [[compact]]. The [[scientific]] field must be a string value containing the substrings "{number}", "{scientificSeparator}", and "{scientificExponent}". The [[compact]] field must be a Record with two fields: "short" and "long". Each of these fields must be a Record with 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 "{number}". Strings descended from "short" must contain the substring "{compactSymbol}", and strings descended from "long" must contain the substring "{compactName}".
Note 2
It is recommended that implementations use the locale data provided by the Common Locale Data Repository (available at http://cldr.unicode.org).

12.4 Properties of the Intl.NumberFormat Prototype Object

The Intl.NumberFormat prototype object is itself an ordinary object. %NumberFormatPrototype% 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.

12.4.1 Intl.NumberFormat.prototype.constructor

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

12.4.2 Intl.NumberFormat.prototype [ @@toStringTag ]

The initial value of the @@toStringTag property is the String value "Object".

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

12.4.3 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 Type(nf) is not Object, throw a TypeError exception.
  3. Let nf be ? UnwrapNumberFormat(nf).
  4. If nf.[[BoundFormat]] is undefined, then
    1. Let F be a new built-in function object as defined in Number Format Functions (12.1.4).
    2. Set F.[[NumberFormat]] to nf.
    3. Set nf.[[BoundFormat]] to F.
  5. 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.

12.4.4 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 ? ToNumeric(value).
  4. Return ? FormatNumericToParts(nf, x).

12.4.5 Intl.NumberFormat.prototype.resolvedOptions ()

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

  1. Let nf be this value.
  2. If Type(nf) is not Object, throw a TypeError exception.
  3. Let nf be ? UnwrapNumberFormat(nf).
  4. Let options be ! ObjectCreate(%ObjectPrototype%).
  5. For each row of Table 5, 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. Perform ! CreateDataPropertyOrThrow(options, p, v).
  6. Return options.
Table 5: Resolved Options of NumberFormat Instances
Internal Slot Property
[[Locale]] "locale"
[[NumberingSystem]] "numberingSystem"
[[Style]] "style"
[[Currency]] "currency"
[[CurrencyDisplay]] "currencyDisplay"
[[CurrencySign]] "currencySign"
[[Unit]] "unit"
[[UnitDisplay]] "unitDisplay"
[[MinimumIntegerDigits]] "minimumIntegerDigits"
[[MinimumFractionDigits]] "minimumFractionDigits"
[[MaximumFractionDigits]] "maximumFractionDigits"
[[MinimumSignificantDigits]] "minimumSignificantDigits"
[[MaximumSignificantDigits]] "maximumSignificantDigits"
[[UseGrouping]] "useGrouping"
[[Notation]] "notation"
[[CompactDisplay]] "compactDisplay"
[[SignDisplay]] "signDisplay"

12.5 Properties of Intl.NumberFormat Instances

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

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

Intl.NumberFormat instances also have several internal slots that are computed by the constructor:

  • [[Locale]] is a String value with the language tag of the locale whose localization is used for formatting.
  • [[DataLocale]] is a String value with the language tag of the nearest locale for which the implementation has data to perform the formatting operation. It will be a parent locale of [[Locale]].
  • [[NumberingSystem]] is a String value with the "type" given in Unicode Technical Standard 35 for the numbering system 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, as defined by Unicode Technical Standard #35, Part 2, Section 6. 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 Number value indicating the minimum integer digits to be used. Numbers will be padded with leading zeroes if necessary.
  • [[MinimumFractionDigits]] and [[MaximumFractionDigits]] are non-negative integer Number values 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 fractionDigits.
  • [[MinimumSignificantDigits]] and [[MaximumSignificantDigits]] are positive integer Number values 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 significantDigits.
  • [[UseGrouping]] is a Boolean value indicating whether a grouping separator should be used.
  • [[RoundingType]] is one of the values fractionDigits, significantDigits, or compactRounding, indicating which rounding strategy to use. If fractionDigits, the number is rounded according to [[MinimumFractionDigits]] and [[MaximumFractionDigits]], as described above. If significantDigits, the number is rounded according to [[MinimumSignificantDigits]] and [[MaximumSignificantDigits]] as described above. If compactRounding, the number is rounded to 1 maximum fraction digit if there is 1 digit before the decimal separator, and otherwise round to 0 fraction digits.
  • [[Notation]] is one of the String values "standard", "scientific", "engineering", or "compact", specifying whether the 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 locale-dependent 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", or "exceptZero", specifying whether to show the sign on negative numbers only, positive and negative numbers including zero, neither positive nor negative numbers, or positive and negative numbers but not zero. In scientific notation, this slot affects the sign display of the mantissa but not the exponent.

Finally, Intl.NumberFormat instances have a [[BoundFormat]] internal slot that caches the function returned by the format accessor (12.4.3).

13 DateTimeFormat Objects

13.1 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 6: Components of date and time formats
Internal Slot 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"
[[Hour]] "hour" "2-digit", "numeric"
[[Minute]] "minute" "2-digit", "numeric"
[[Second]] "second" "2-digit", "numeric"
[[TimeZoneName]] "timeZoneName" "short", "long"

13.1.1 InitializeDateTimeFormat ( dateTimeFormat, locales, options )

The abstract operation InitializeDateTimeFormat accepts the arguments dateTimeFormat (which must be an object), locales, and options. It initializes dateTimeFormat as a DateTimeFormat object. This abstract operation functions as follows:

The following algorithm refers to the type nonterminal from UTS 35's Unicode Locale Identifier grammar.

  1. Let requestedLocales be ? CanonicalizeLocaleList(locales).
  2. Let options be ? ToDateTimeOptions(options, "any", "date").
  3. Let opt be a new Record.
  4. Let matcher be ? GetOption(options, "localeMatcher", "string", « "lookup", "best fit" », "best fit").
  5. Set opt.[[localeMatcher]] to matcher.
  6. Let calendar be ? GetOption(options, "calendar", "string", undefined, undefined).
  7. If calendar is not undefined, then
    1. If calendar does not match the Unicode Locale Identifier type nonterminal, throw a RangeError exception.
  8. Set opt.[[ca]] to calendar.
  9. Let numberingSystem be ? GetOption(options, "numberingSystem", "string", undefined, undefined).
  10. If numberingSystem is not undefined, then
    1. If numberingSystem does not match the Unicode Locale Identifier type nonterminal, throw a RangeError exception.
  11. Set opt.[[nu]] to numberingSystem.
  12. Let hour12 be ? GetOption(options, "hour12", "boolean", undefined, undefined).
  13. Let hourCycle be ? GetOption(options, "hourCycle", "string", « "h11", "h12", "h23", "h24" », undefined).
  14. If hour12 is not undefined, then
    1. Let hourCycle be null.
  15. Set opt.[[hc]] to hourCycle.
  16. Let localeData be %DateTimeFormat%.[[LocaleData]].
  17. Let r be ResolveLocale( %DateTimeFormat%.[[AvailableLocales]], requestedLocales, opt, %DateTimeFormat%.[[RelevantExtensionKeys]], localeData).
  18. Set dateTimeFormat.[[Locale]] to r.[[locale]].
  19. Let calendar be r.[[ca]].
  20. Set dateTimeFormat.[[Calendar]] to calendar.
  21. Set dateTimeFormat.[[HourCycle]] to r.[[hc]].
  22. Set dateTimeFormat.[[NumberingSystem]] to r.[[nu]].
  23. Let dataLocale be r.[[dataLocale]].
  24. Let timeZone be ? Get(options, "timeZone").
  25. If timeZone is not undefined, then
    1. Let timeZone be ? ToString(timeZone).
    2. If the result of IsValidTimeZoneName(timeZone) is false, then
      1. Throw a RangeError exception.
    3. Let timeZone be CanonicalizeTimeZoneName(timeZone).
  26. Else,
    1. Let timeZone be DefaultTimeZone().
  27. Set dateTimeFormat.[[TimeZone]] to timeZone.
  28. Let opt be a new Record.
  29. For each row of Table 6, except the header row, in table order, do
    1. Let prop be the name given in the Property column of the row.
    2. Let value be ? GetOption(options, prop, "string", « the strings given in the Values column of the row », undefined).
    3. Set opt.[[<prop>]] to value.
  30. Let dataLocaleData be localeData.[[<dataLocale>]].
  31. Let formats be dataLocaleData.[[formats]].[[<calendar>]].
  32. Let matcher be ? GetOption(options, "formatMatcher", "string", « "basic", "best fit" », "best fit").
  33. If matcher is "basic", then
    1. Let bestFormat be BasicFormatMatcher(opt, formats).
  34. Else,
    1. Let bestFormat be BestFitFormatMatcher(opt, formats).
  35. For each row in Table 6, except the header row, in table order, do
    1. Let prop be the name given in the Property column of the row.
    2. Let p be bestFormat.[[<prop>]].
    3. If p not undefined, then
      1. Set dateTimeFormat's internal slot whose name is the Internal Slot column of the row to p.
  36. If dateTimeFormat.[[Hour]] is not undefined, then
    1. Let hcDefault be dataLocaleData.[[hourCycle]].
    2. Let hc be dateTimeFormat.[[HourCycle]].
    3. If hc is null, then
      1. Set hc to hcDefault.
    4. If hour12 is not undefined, then
      1. If hour12 is true, then
        1. If hcDefault is "h11" or "h23", then
          1. Set hc to "h11".
        2. Else,
          1. Set hc to "h12".
      2. Else,
        1. Assert: hour12 is false.
        2. If hcDefault is "h11" or "h23", then
          1. Set hc to "h23".
        3. Else,
          1. Set hc to "h24".
    5. Set dateTimeFormat.[[HourCycle]] to hc.
    6. If dateTimeformat.[[HourCycle]] is "h11" or "h12", then
      1. Let pattern be bestFormat.[[pattern12]].
    7. Else,
      1. Let pattern be bestFormat.[[pattern]].
  37. Else,
    1. Set dateTimeFormat.[[HourCycle]] to undefined.
    2. Let pattern be bestFormat.[[pattern]].
  38. Set dateTimeFormat.[[Pattern]] to pattern.
  39. Return dateTimeFormat.

13.1.2 ToDateTimeOptions ( options, required, defaults )

When the ToDateTimeOptions abstract operation is called with arguments options, required, and defaults, the following steps are taken:

  1. If options is undefined, let options be null; otherwise let options be ? ToObject(options).
  2. Let options be ObjectCreate(options).
  3. Let needDefaults be true.
  4. If required is "date" or "any", then
    1. For each of the property names "weekday", "year", "month", "day", do
      1. Let prop be the property name.
      2. Let value be ? Get(options, prop).
      3. If value is not undefined, let needDefaults be false.
  5. If required is "time" or "any", then
    1. For each of the property names "hour", "minute", "second", do
      1. Let prop be the property name.
      2. Let value be ? Get(options, prop).
      3. If value is not undefined, let needDefaults be false.
  6. If needDefaults is true and defaults is either "date" or "all", then
    1. For each of the property names "year", "month", "day", do
      1. Perform ? CreateDataPropertyOrThrow(options, prop, "numeric").
  7. If needDefaults is true and defaults is either "time" or "all", then
    1. For each of the property names "hour", "minute", "second", do
      1. Perform ? CreateDataPropertyOrThrow(options, prop, "numeric").
  8. Return options.

13.1.3 BasicFormatMatcher ( options, formats )

When the BasicFormatMatcher abstract operation is called with two arguments options and formats, the following steps are taken:

  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 bestScore be -Infinity.
  8. Let bestFormat be undefined.
  9. Assert: Type(formats) is List.
  10. For each element format of formats in List order, do
    1. Let score be 0.
    2. For each property shown in Table 6, do
      1. Let optionsProp be options.[[<property>]].
      2. Let formatProp be format.[[<property>]].
      3. If optionsProp is undefined and formatProp is not undefined, then decrease score by additionPenalty.
      4. Else if optionsProp is not undefined and formatProp is undefined, then decrease score by removalPenalty.
      5. Else if optionsProp ≠ formatProp,
        1. Let values be « "2-digit", "numeric", "narrow", "short", "long" ».
        2. Let optionsPropIndex be the index of optionsProp within values.
        3. Let formatPropIndex be the index of formatProp within values.
        4. Let delta be max(min(formatPropIndex - optionsPropIndex, 2), -2).
        5. If delta = 2, decrease score by longMorePenalty.
        6. Else if delta = 1, decrease score by shortMorePenalty.
        7. Else if delta = -1, decrease score by shortLessPenalty.
        8. Else if delta = -2, decrease score by longLessPenalty.
    3. If score > bestScore, then
      1. Let bestScore be score.
      2. Let bestFormat be format.
  11. Return bestFormat.

13.1.4 BestFitFormatMatcher ( options, formats )

When the BestFitFormatMatcher abstract operation is called with two arguments options and formats, it performs implementation dependent steps, which should return 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.

13.1.5 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. Assert: Type(dtf) is Object and dtf has an [[InitializedDateTimeFormat]] internal slot.
  3. If date is not provided or is undefined, then
    1. Let x be Call(%Date_now%, undefined).
  4. Else,
    1. Let x be ? ToNumber(date).
  5. Return ? FormatDateTime(dtf, x).

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

13.1.6 PartitionDateTimePattern ( dateTimeFormat, x )

The PartitionDateTimePattern abstract operation is called with arguments dateTimeFormat (which must be an object initialized as a DateTimeFormat) and x (which must be a Number value), interprets x as a time value as specified in ES2015, 20.4.1.1, and creates the corresponding parts according to the effective locale and the formatting options of dateTimeFormat. The following steps are taken:

  1. Let x be TimeClip(x).
  2. If x is NaN, throw a RangeError exception.
  3. Let locale be dateTimeFormat.[[Locale]].
  4. Let nfOptions be ObjectCreate(null).
  5. Perform ! CreateDataPropertyOrThrow(nfOptions, "useGrouping", false).
  6. Let nf be ? Construct(%NumberFormat%, « locale, nfOptions »).
  7. Let nf2Options be ObjectCreate(null).
  8. Perform ! CreateDataPropertyOrThrow(nf2Options, "minimumIntegerDigits", 2).
  9. Perform ! CreateDataPropertyOrThrow(nf2Options, "useGrouping", false).
  10. Let nf2 be ? Construct(%NumberFormat%, « locale, nf2Options »).
  11. Let tm be ToLocalTime(x, dateTimeFormat.[[Calendar]], dateTimeFormat.[[TimeZone]]).
  12. Let result be a new empty List.
  13. Let patternParts be PartitionPattern(dateTimeFormat.[[Pattern]]).
  14. For each element patternPart of patternParts, in List order, do
    1. Let p be patternPart.[[Type]].
    2. If p is "literal", then
      1. Append a new Record { [[Type]]: "literal", [[Value]]: patternPart.[[Value]] } as the last element of the list result.
    3. Else if p matches a Property column of the row in Table 6, then
      1. Let f be the value of dateTimeFormat's internal slot whose name is the Internal Slot column of the matching row.
      2. Let v be the value of tm's field whose name is the Internal Slot column of the matching row.
      3. If p is "year" and v ≤ 0, let v be 1 - v.
      4. If p is "month", increase v by 1.
      5. If p is "hour" and dateTimeFormat.[[HourCycle]] is "h11" or "h12", then
        1. Let v be v modulo 12.
        2. If v is 0 and dateTimeFormat.[[HourCycle]] is "h12", let v be 12.
      6. If p is "hour" and dateTimeFormat.[[HourCycle]] is "h24", then
        1. If v is 0, let v be 24.
      7. If f is "numeric", then
        1. Let fv be FormatNumeric(nf, v).
      8. Else if f is "2-digit", then
        1. Let fv be FormatNumeric(nf2, v).
        2. If the "length" property of fv is greater than 2, let fv be the substring of fv containing the last two characters.
      9. Else if f is "narrow", "short", or "long", then let fv be a String value representing f in the desired form; the String value depends upon the implementation and the effective locale and calendar of dateTimeFormat. If p is "month", then the String value may also depend on whether dateTimeFormat has a [[Day]] internal slot. If p is "timeZoneName", then the String value may also depend on the value of the [[InDST]] field of tm. If p is "era", then the String value may also depend on whether dateTimeFormat has a [[Era]] internal slot and if the implementation does not have a localized representation of f, then use f itself.
      10. Append a new Record { [[Type]]: p, [[Value]]: fv } as the last element of the list result.
    4. Else if p is equal to "ampm", then
      1. Let v be tm.[[Hour]].
      2. If v is greater than 11, then
        1. Let fv be an implementation and locale dependent String value representing "post meridiem".
      3. Else,
        1. Let fv be an implementation and locale dependent String value representing "ante meridiem".
      4. Append a new Record { [[Type]]: "dayPeriod", [[Value]]: fv } as the last element of the list result.
    5. Else if p is equal to "relatedYear", then
      1. Let v be tm.[[RelatedYear]].
      2. Let fv be FormatNumber(nf, v).
      3. Append a new Record { [[Type]]: "relatedYear", [[Value]]: fv } as the last element of the list result.
    6. Else if p is equal to "yearName", then
      1. Let v be tm.[[YearName]].
      2. Append a new Record { [[Type]]: "yearName", [[Value]]: v } as the last element of the list result.
    7. Else,
      1. Let unknown be an implementation-, locale-, and numbering system-dependent String based on x and p.
      2. Append a new Record { [[Type]]: "unknown", [[Value]]: unknown } as the last element of result.
  15. Return result.
Note 1
It is recommended that implementations use the locale and calendar dependent strings provided by the Common Locale Data Repository (available at http://cldr.unicode.org), and use CLDR "abbreviated" strings for DateTimeFormat "short" strings, and CLDR "wide" strings for DateTimeFormat "long" strings.
Note 2
It is recommended that implementations use the time zone information of the IANA Time Zone Database.

13.1.7 FormatDateTime( dateTimeFormat, x )

The FormatDateTime abstract operation is called with arguments dateTimeFormat (which must be an object initialized as a DateTimeFormat) and x (which must be a Number value), and performs the following steps:

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

13.1.8 FormatDateTimeToParts ( dateTimeFormat, x )

The FormatDateTimeToParts abstract operation is called with arguments dateTimeFormat (which must be an object initialized as a DateTimeFormat) and x (which must be a Number value), and performs the following steps:

  1. Let parts be ? PartitionDateTimePattern(dateTimeFormat, x).
  2. Let result be ArrayCreate(0).
  3. Let n be 0.
  4. For each part in parts, do
    1. Let O be ObjectCreate(%ObjectPrototype%).
    2. Perform ! CreateDataPropertyOrThrow(O, "type", part.[[Type]]).
    3. Perform ! CreateDataPropertyOrThrow(O, "value", part.[[Value]]).
    4. Perform ! CreateDataProperty(result, ! ToString(n), O).
    5. Increment n by 1.
  5. Return result.

13.1.9 ToLocalTime ( t, calendar, timeZone )

When the ToLocalTime abstract operation is called with arguments t, calendar, and timeZone, the following steps are taken:

  1. Assert: Type(t) is Number.
  2. If calendar is "gregory",
    1. Let timeZoneOffset be the value calculated according to LocalTZA(t, true) where the local time zone is replaced with timezone timeZone.
    2. Let tz be the time value t + timeZoneOffset.
    3. Return a record with fields calculated from tz according to Table 7.
  3. Else,
    1. Return a record with the fields of Column 1 of Table 7 calculated from t for the given calendar and timeZone. The calculations should use best available information about the specified calendar and timeZone, including current and historical information about time zone offsets from UTC and daylight saving time rules.
Table 7: Record returned by ToLocalTime
Field Value Calculation for Gregorian Calendar
[[Weekday]] WeekDay(tz) specified in ES2020's Week Day
[[Era]] Let year be YearFromTime(tz) specified in ES2020's Year Number. If year is less than 0, return 'BC', else, return 'AD'.
[[Year]] YearFromTime(tz) specified in ES2020's Year Number
[[RelatedYear]] undefined
[[YearName]] undefined
[[Month]] MonthFromTime(tz) specified in ES2020's Month Number
[[Day]] DateFromTime(tz) specified in ES2020's Date Number
[[Hour]] HourFromTime(tz) specified in ES2020's Hours, Minutes, Second, and Milliseconds
[[Minute]] MinuteFromTime(tz) specified in ES2020's Hours, Minutes, Second, and Milliseconds
[[Second]] SecondFromTime(tz) specified in ES2020's Hours, Minutes, Second, and Milliseconds
[[InDST]] Calculate true or false using the best available information about the specified calendar and timeZone, including current and historical information about time zone offsets from UTC and daylight saving time rules.
Note
It is recommended that implementations use the time zone information of the IANA Time Zone Database.

13.1.10 UnwrapDateTimeFormat( dtf )

The UnwrapDateTimeFormat abstract operation gets the underlying DateTimeFormat operation for various methods which implement ECMA-402 v1 semantics for supporting initializing existing Intl objects.

  1. Assert: Type(dtf) is Object.
  1. If dtf does not have an [[InitializedDateTimeFormat]] internal slot and ? InstanceofOperator(dtf, %DateTimeFormat%) is true, then
    1. Let dtf be ? Get(dtf, %Intl%.[[FallbackSymbol]]).
  1. Perform ? RequireInternalSlot(dtf, [[InitializedDateTimeFormat]]).
  2. Return dtf.
Note
See 8.1 Note 1 for the motivation of the normative optional text.

13.2 The Intl.DateTimeFormat Constructor

The Intl.DateTimeFormat constructor is the %DateTimeFormat% intrinsic object and a standard built-in property of the Intl object. Behaviour common to all service constructor properties of the Intl object is specified in 9.1.

13.2.1 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 active function object, else let newTarget be NewTarget.
  2. Let dateTimeFormat be ? OrdinaryCreateFromConstructor(newTarget, "%DateTimeFormatPrototype%", « [[InitializedDateTimeFormat]], [[Locale]], [[Calendar]], [[NumberingSystem]], [[TimeZone]], [[Weekday]], [[Era]], [[Year]], [[Month]], [[Day]], [[Hour]], [[Minute]], [[Second]], [[TimeZoneName]], [[HourCycle]], [[Pattern]], [[BoundFormat]] »).
  3. Perform ? InitializeDateTimeFormat(dateTimeFormat, locales, options).
  1. Let this be the this value.
  2. If NewTarget is undefined and Type(this) is Object and ? InstanceofOperator(this, %DateTimeFormat%) is true, then
    1. Perform ? DefinePropertyOrThrow(this, %Intl%.[[FallbackSymbol]], PropertyDescriptor{ [[Value]]: dateTimeFormat, [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }).
    2. Return this.
  1. Return dateTimeFormat.
Note
See 8.1 Note 1 for the motivation of the normative optional text.

13.3 Properties of the Intl.DateTimeFormat Constructor

The Intl.DateTimeFormat constructor has the following properties:

13.3.1 Intl.DateTimeFormat.prototype

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

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

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

The value of the "length" property of the supportedLocalesOf method is 1.

13.3.3 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", "nu", "hc" ».

Note 1
Unicode Technical Standard 35 describes three locale extension keys that are relevant to date and time formatting, "ca" for calendar, "tz" for time zone, "hc" for hour cycle, and implicitly "nu" for the numbering system of the number format used for numbers within the date format. DateTimeFormat, however, requires that the time zone is specified through the "timeZone" 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, 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 a String value equal to "h11", "h12", "h23", or "h24".
  • [[LocaleData]].[[<locale>]] must have a [[formats]] field. This formats field must have a [[<calendar>]] field for all calendar values calendar. The value of this field must be a list of records, each of which has a subset of the fields shown in Table 6, where each field must have one of the values specified for the field in Table 6. Multiple records in a list may use the same subset of the fields as long as they have different values for the fields. The following subsets must be available for each locale:
    • weekday, year, month, day, hour, minute, second
    • weekday, year, month, day
    • year, month, day
    • year, month
    • month, day
    • hour, minute, second
    • hour, minute
    Each of the records must also have a [[pattern]] field, whose value is a String value that 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 an hour field, it must also have a [[pattern12]] field, whose value is a String value that, in addition to the substrings of the [[pattern]] field, contains a substring "{ampm}". If the record has a [[year]] field, the [[pattern]] and [[pattern12]] values may contain the substrings "{yearName}" and "{relatedYear}".

EXAMPLE An implementation might include the following record as part of its English locale data: {[[hour]]: "numeric", [[minute]]: "2-digit", [[second]]: "2-digit", [[pattern]]: "{hour}:{minute}:{second}", [[pattern12]]: "{hour}:{minute}:{second} {ampm}"}.

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

13.4 Properties of the Intl.DateTimeFormat Prototype Object

The Intl.DateTimeFormat prototype object is itself an ordinary object. %DateTimeFormatPrototype% 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.

13.4.1 Intl.DateTimeFormat.prototype.constructor

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

13.4.2 Intl.DateTimeFormat.prototype [ @@toStringTag ]

The initial value of the @@toStringTag property is the String value "Object".

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

13.4.3 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 this value.
  2. If Type(dtf) is not Object, throw a TypeError exception.
  3. Let dtf be ? UnwrapDateTimeFormat(dtf).
  4. If dtf.[[BoundFormat]] is undefined, then
    1. Let F be a new built-in function object as defined in DateTime Format Functions (13.1.5).
    2. Set F.[[DateTimeFormat]] to dtf.
    3. 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.

13.4.4 Intl.DateTimeFormat.prototype.formatToParts ( date )

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

  1. Let dtf be this value.
  2. Perform ? RequireInternalSlot(dtf, [[InitializedDateTimeFormat]]).
  3. If date is undefined, then
    1. Let x be Call(%Date_now%, undefined).
  4. Else,
    1. Let x be ? ToNumber(date).
  5. Return ? FormatDateTimeToParts(dtf, x).

13.4.5 Intl.DateTimeFormat.prototype.resolvedOptions ()

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

  1. Let dtf be this value.
  2. If Type(dtf) is not Object, throw a TypeError exception.
  3. Let dtf be ? UnwrapDateTimeFormat(dtf).
  4. Let options be ! ObjectCreate(%ObjectPrototype%).
  5. For each row of Table 8, except the header row, in table order, do
    1. Let p be the Property value of the current row.
    2. If p is "hour12", then
      1. Let hc be dtf.[[HourCycle]].
      2. If hc is "h11" or "h12", let v be true.
      3. Else if, hc is "h23" or "h24", let v be false.
      4. Else, let v be undefined.
    3. Else,
      1. Let v be the value of dtf's internal slot whose name is the Internal Slot value of the current row.
    4. If v is not undefined, then
      1. Perform ! CreateDataPropertyOrThrow(options, p, v).
  6. Return options.
Table 8: Resolved Options of DateTimeFormat Instances
Internal Slot Property
[[Locale]] "locale"
[[Calendar]] "calendar"
[[NumberingSystem]] "numberingSystem"
[[TimeZone]] "timeZone"
[[HourCycle]] "hourCycle"
"hour12"
[[Weekday]] "weekday"
[[Era]] "era"
[[Year]] "year"
[[Month]] "month"
[[Day]] "day"
[[Hour]] "hour"
[[Minute]] "minute"
[[Second]] "second"
[[TimeZoneName]] "timeZoneName"

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 ECMAScript 2020 Internationalization API, the "timeZone" property will be the name of the default time zone if no "timeZone" property was provided in the options object provided to the Intl.DateTimeFormat 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.

13.5 Properties of Intl.DateTimeFormat Instances

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

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

Intl.DateTimeFormat instances also have several internal slots that are computed by the constructor:

  • [[Locale]] is a String value with the language tag of the locale whose localization is used for formatting.
  • [[Calendar]] is a String value with the "type" given in Unicode Technical Standard 35 for the calendar used for formatting.
  • [[NumberingSystem]] is a String value with the "type" given in Unicode Technical Standard 35 for the numbering system used for formatting.
  • [[TimeZone]] is a String value with the IANA time zone name of the time zone used for formatting.
  • [[Weekday]], [[Era]], [[Year]], [[Month]], [[Day]], [[Hour]], [[Minute]], [[Second]], [[TimeZoneName]] are each either undefined, indicating that the component is not used for formatting, or one of the String values given in Table 6, indicating how the component should be presented in the formatted output.
  • [[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 [[Hour]] is not undefined.
  • [[Pattern]] is a String value as described in 13.3.3.

Finally, Intl.DateTimeFormat instances have a [[BoundFormat]] internal slot that caches the function returned by the format accessor (13.4.3).

14 RelativeTimeFormat Objects

14.1 Abstract Operations for RelativeTimeFormat Objects

14.1.1 InitializeRelativeTimeFormat ( relativeTimeFormat, locales, options )

The abstract operation InitializeRelativeTimeFormat accepts the arguments relativeTimeFormat (which must be an object), locales, and options. It initializes relativeTimeFormat as a RelativeTimeFormat object.

The following algorithm refers to UTS 35's Unicode Language and Locale Identifiers grammar. The following steps are taken:

  1. Let requestedLocales be ? CanonicalizeLocaleList(locales).
  2. If options is undefined, then
    1. Let options be ObjectCreate(null).
  3. Else,
    1. Let options be ? ToObject(options).
  4. Let opt be a new Record.
  5. Let matcher be ? GetOption(options, "localeMatcher", "string", «"lookup", "best fit"», "best fit").
  6. Set opt.[[LocaleMatcher]] to matcher.
  7. Let numberingSystem be ? GetOption(options, "numberingSystem", "string", undefined, undefined).
  8. If numberingSystem is not undefined, then
    1. If numberingSystem does not match the type sequence (from UTS 35 Unicode Locale Identifier, section 3.2), throw a RangeError exception.
  9. Set opt.[[nu]] to numberingSystem.
  10. Let localeData be %RelativeTimeFormat%.[[LocaleData]].
  11. Let r be ResolveLocale(%RelativeTimeFormat%.[[AvailableLocales]], requestedLocales, opt, %RelativeTimeFormat%.[[RelevantExtensionKeys]], localeData).
  12. Let locale be r.[[Locale]].
  13. Set relativeTimeFormat.[[Locale]] to locale.
  14. Set relativeTimeFormat.[[DataLocale]] to r.[[DataLocale]].
  15. Set relativeTimeFormat.[[NumberingSystem]] to r.[[nu]].
  16. Let s be ? GetOption(options, "style", "string", «"long", "short", "narrow"», "long").
  17. Set relativeTimeFormat.[[Style]] to s.
  18. Let numeric be ? GetOption(options, "numeric", "string", «"always", "auto"», "always").
  19. Set relativeTimeFormat.[[Numeric]] to numeric.
  20. Let relativeTimeFormat.[[NumberFormat]] be ! Construct(%NumberFormat%, « locale »).
  21. Let relativeTimeFormat.[[PluralRules]] be ! Construct(%PluralRules%, « locale »).
  22. Return relativeTimeFormat.

14.1.2 SingularRelativeTimeUnit ( unit )

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

14.1.3 PartitionRelativeTimePattern ( relativeTimeFormat, value, unit )

When the PartitionRelativeTimePattern abstract operation is called with arguments relativeTimeFormat, value, and unit it returns a String value representing value (which must be a Number value) according to the effective locale and the formatting options of relativeTimeFormat.

  1. Assert: relativeTimeFormat has an [[InitializedRelativeTimeFormat]] internal slot.
  2. Assert: Type(value) is Number.
  3. Assert: Type(unit) is String.
  4. If value is NaN, +∞, or -∞, throw a RangeError exception.
  5. Let unit be ? SingularRelativeTimeUnit(unit).
  6. Let localeData be %RelativeTimeFormat%.[[LocaleData]].
  7. Let dataLocale be relativeTimeFormat.[[DataLocale]].
  8. Let fields be localeData.[[<dataLocale>]].
  9. Let style be relativeTimeFormat.[[Style]].
  10. If style is equal to "short", then
    1. Let entry be the string-concatenation of unit and "-short".
  11. Else if style is equal to "narrow", then
    1. Let entry be the string-concatenation of unit and "-narrow".
  12. Else,
    1. Let entry be unit.
  13. If fields doesn't have a field [[<entry>]], then
    1. Let entry be unit.
  14. Let patterns be fields.[[<entry>]].
  15. Let numeric be relativeTimeFormat.[[Numeric]].
  16. If numeric is equal to "auto", then
    1. Let valueString be ToString(value).
    2. If patterns has a field [[<valueString>]], then
      1. Let result be patterns.[[<valueString>]].
      2. Return a List containing the Record { [[Type]]: "literal", [[Value]]: result }.
  17. If value is -0 or if value is less than 0, then
    1. Let tl be "past".
  18. Else,
    1. Let tl be "future".
  19. Let po be patterns.[[<tl>]].
  20. Let fv be ! PartitionNumberPattern(relativeTimeFormat.[[NumberFormat]], value).
  21. Let pr be ! ResolvePlural(relativeTimeFormat.[[PluralRules]], value).
  22. Let pattern be po.[[<pr>]].
  23. Return ! MakePartsList(pattern, unit, fv).

14.1.4 MakePartsList ( pattern, unit, parts )

The MakePartsList abstract operation is called with arguments pattern, a pattern String, unit, a String, and parts, a List of Records representing a formatted Number.

Note
Example: 
          MakePartsList("AA{0}BB", "hour", « { [[Type]]: "integer", [[Value]]: "15" } » )

        Output (List of Records):
          «
            { [[Type]]: "literal", [[Value]]: "AA"},
            { [[Type]]: "integer", [[Value]]: "15", [[Unit]]: "hour"},
            { [[Type]]: "literal", [[Value]]: "BB"}
          »
  1. Let patternParts be PartitionPattern(pattern).
  2. Let result be a new empty List.
  3. For each element patternPart of patternParts, in List order, do
    1. If patternPart.[[Type]] is "literal", then
      1. Append Record { [[Type]]: "literal", [[Value]]: patternPart.[[Value]] } to result.
    2. Else,
      1. Assert: patternPart.[[Type]] is "0".
      2. For each part in parts, do
        1. Append Record { [[Type]]: part.[[Type]], [[Value]]: part.[[Value]], [[Unit]]: unit } to result.
  4. Return result.

14.1.5 FormatRelativeTime ( relativeTimeFormat, value, unit )

The FormatRelativeTime abstract operation is called with arguments relativeTimeFormat (which must be an object initialized as a RelativeTimeFormat), value (which must be a Number value), and unit (which must be a String denoting the value unit) and performs the following steps:

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

14.1.6 FormatRelativeTimeToParts ( relativeTimeFormat, value, unit )

The FormatRelativeTimeToParts abstract operation is called with arguments relativeTimeFormat (which must be an object initialized as a RelativeTimeFormat), value (which must be a Number value), and unit (which must be a String denoting the value unit) and performs the following steps:

  1. Let parts be ? PartitionRelativeTimePattern(relativeTimeFormat, value, unit).
  2. Let result be ArrayCreate(0).
  3. Let n be 0.
  4. For each part in parts, do
    1. Let O be ObjectCreate(%ObjectPrototype%).
    2. Perform ! CreateDataPropertyOrThrow(O, "type", part.[[Type]]).
    3. Perform ! CreateDataPropertyOrThrow(O, "value", part.[[Value]]).
    4. If part has a [[Unit]] field,
      1. Perform ! CreateDataPropertyOrThrow(O, "unit", part.[[Unit]]).
    5. Perform ! CreateDataPropertyOrThrow(result, ! ToString(n), O).
    6. Increment n by 1.
  5. Return result.

14.2 The Intl.RelativeTimeFormat Constructor

The RelativeTimeFormat constructor is the %RelativeTimeFormat% intrinsic object and a standard built-in property of the Intl object. Behaviour common to all service constructor properties of the Intl object is specified in 9.1.

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

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

  1. If NewTarget is undefined, throw a TypeError exception.
  2. Let relativeTimeFormat be ? OrdinaryCreateFromConstructor(NewTarget, "%RelativeTimeFormatPrototype%", « [[InitializedRelativeTimeFormat]], [[Locale]], [[DataLocale]], [[Style]], [[Numeric]], [[NumberFormat]], [[NumberingSystem]], [[PluralRules]] »).
  3. Return ? InitializeRelativeTimeFormat(relativeTimeFormat, locales, options).

14.3 Properties of the Intl.RelativeTimeFormat Constructor

The Intl.RelativeTimeFormat constructor has the following properties:

14.3.1 Intl.RelativeTimeFormat.prototype

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

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

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

When the supportedLocalesOf method of %RelativeTimeFormat% is called, the following steps are taken:

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

14.3.3 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" ».

Note 1
Unicode Technical Standard 35 implicitly describes one locale extension key that is relevant to relative time formatting, "nu" for numbering system.

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 http://cldr.unicode.org/).

14.4 Properties of the Intl.RelativeTimeFormat Prototype Object

The Intl.RelativeTimeFormat prototype object is itself an ordinary object. %RelativeTimeFormatPrototype% 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.

14.4.1 Intl.RelativeTimeFormat.prototype.constructor

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

14.4.2 Intl.RelativeTimeFormat.prototype[ @@toStringTag ]

The initial value of the @@toStringTag property is the string value "Intl.RelativeTimeFormat".

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

14.4.3 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 ? RequireInternalSlot(relativeTimeFormat, [[InitializedRelativeTimeFormat]]).
  3. Let value be ? ToNumber(value).
  4. Let unit be ? ToString(unit).
  5. Return ? FormatRelativeTime(relativeTimeFormat, value, unit).

14.4.4 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 ? RequireInternalSlot(relativeTimeFormat, [[InitializedRelativeTimeFormat]]).
  3. Let value be ? ToNumber(value).
  4. Let unit be ? ToString(unit).
  5. Return ? FormatRelativeTimeToParts(relativeTimeFormat, value, unit).

14.4.5 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 ? RequireInternalSlot(relativeTimeFormat, [[InitializedRelativeTimeFormat]]).
  3. Let options be ! ObjectCreate(%ObjectPrototype%).
  4. For each row of Table 9, 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 relativeTimeFormat's internal slot whose name is the Internal Slot value of the current row.
    3. Assert: v is not undefined.
    4. Perform ! CreateDataPropertyOrThrow(options, p, v).
  5. Return options.
Table 9: Resolved Options of RelativeTimeFormat Instances
Internal Slot Property
[[Locale]] "locale"
[[Style]] "style"
[[Numeric]] "numeric"
[[NumberingSystem]] "numberingSystem"

14.5 Properties of Intl.RelativeTimeFormat Instances

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

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

Intl.RelativeTimeFormat instances also have several internal slots that are computed by the constructor:

  • [[Locale]] is a String value with the language tag of the locale whose localization is used for formatting.
  • [[DataLocale]] is a String value with the language tag of the nearest locale for which the implementation has data to perform the formatting operation. It will be a parent locale of [[Locale]].
  • [[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]] is a String value with the "type" given in Unicode Technical Standard 35 for the numbering system used for formatting.
  • [[PluralRules]] is an Intl.PluralRules object used for formatting.

15 PluralRules Objects

15.1 Abstract Operations for PluralRules Objects

15.1.1 InitializePluralRules ( pluralRules, locales, options )

The abstract operation InitializePluralRules accepts the arguments pluralRules (which must be an object), locales, and options. It initializes pluralRules as a PluralRules object. The following steps are taken:

  1. Let requestedLocales be ? CanonicalizeLocaleList(locales).
  2. If options is undefined, then
    1. Let options be ObjectCreate(null).
  3. Else
    1. Let options be ? ToObject(options).
  4. Let opt be a new Record.
  5. Let matcher be ? GetOption(options, "localeMatcher", "string", « "lookup", "best fit" », "best fit").
  6. Set opt.[[localeMatcher]] to matcher.
  7. Let t be ? GetOption(options, "type", "string", « "cardinal", "ordinal" », "cardinal").
  8. Set pluralRules.[[Type]] to t.
  9. Perform ? SetNumberFormatDigitOptions(pluralRules, options, 0, 3, "standard").
  10. Let localeData be %PluralRules%.[[LocaleData]].
  11. Let r be ResolveLocale(%PluralRules%.[[AvailableLocales]], requestedLocales, opt, %PluralRules%.[[RelevantExtensionKeys]], localeData).
  12. Set pluralRules.[[Locale]] to the value of r.[[locale]].
  13. Return pluralRules.

15.1.2 GetOperands ( s )

When the GetOperands abstract operation is called with argument s, it performs the following steps:

  1. Assert: Type(s) is String.
  2. Let n be ! ToNumber(s).
  3. Assert: n is finite.
  4. Let dp be ! Call(%StringProto_indexOf%, s, « "." »).
  5. If dp = -1, then
    1. Set iv to n.
    2. Let f be 0.
    3. Let v be 0.
  6. Else,
    1. Let iv be the substring of s from position 0, inclusive, to position dp, exclusive.
    2. Let fv be the substring of s from position dp, exclusive, to the end of s.
    3. Let f be ! ToNumber(fv).
    4. Let v be the length of fv.
  7. Let i be abs(! ToNumber(iv)).
  8. If f ≠ 0, then
    1. Let ft be the value of fv stripped of trailing "0".
    2. Let w be the length of ft.
    3. Let t be ! ToNumber(ft).
  9. Else,
    1. Let w be 0.
    2. Let t be 0.
  10. Return a new Record { [[Number]]: n, [[IntegerDigits]]: i, [[NumberOfFractionDigits]]: v, [[NumberOfFractionDigitsWithoutTrailing]]: w, [[FractionDigits]]: f, [[FractionDigitsWithoutTrailing]]: t }.
Table 10: Plural Rules Operands Record Fields
Internal Slot Type Description
[[Number]] Number Absolute value of the source number (integer and decimals)
[[IntegerDigits]] Number Number of digits of [[Number]].
[[NumberOfFractionDigits]] Number Number of visible fraction digits in [[Number]], with trailing zeroes.
[[NumberOfFractionDigitsWithoutTrailing]] Number Number of visible fraction digits in [[Number]], without trailing zeroes.
[[FractionDigits]] Number Number of visible fractional digits in [[Number]], with trailing zeroes.
[[FractionDigitsWithoutTrailing]] Number Number of visible fractional digits in [[Number]], without trailing zeroes.

15.1.3 PluralRuleSelect ( locale, type, n, operands )

When the PluralRuleSelect abstract operation is called with four arguments, it performs an implementation-dependent algorithm to map n to the appropriate plural representation of the Plural Rules Operands Record operands by selecting the rules denoted by type for the corresponding locale, or the String value "other".

15.1.4 ResolvePlural ( pluralRules, n )

When the ResolvePlural abstract operation is called with arguments pluralRules (which must be an object initialized as a PluralRules) and n (which must be a Number value), it returns a String value representing the plural form of n according to the effective locale and the options of pluralRules. The following steps are taken:

  1. Assert: Type(pluralRules) is Object.
  2. Assert: pluralRules has an [[InitializedPluralRules]] internal slot.
  3. Assert: Type(n) is Number.
  4. If n is not a finite Number, then
    1. Return "other".
  5. Let locale be pluralRules.[[Locale]].
  6. Let type be pluralRules.[[Type]].
  7. Let res be ! FormatNumericToString(pluralRules, n).
  8. Let s be res.[[FormattedString]].
  9. Let operands be ? GetOperands(s).
  10. Return ? PluralRuleSelect(locale, type, n, operands).

15.2 The Intl.PluralRules Constructor

The PluralRules constructor is the %PluralRules% intrinsic object and a standard built-in property of the Intl object. Behaviour common to all service constructor properties of the Intl object is specified in 9.1.

15.2.1 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, "%PluralRulesPrototype%", « [[InitializedPluralRules]], [[Locale]], [[Type]], [[MinimumIntegerDigits]], [[MinimumFractionDigits]], [[MaximumFractionDigits]], [[MinimumSignificantDigits]], [[MaximumSignificantDigits]], [[RoundingType]] »).
  3. Return ? InitializePluralRules(pluralRules, locales, options).

15.3 Properties of the Intl.PluralRules Constructor

The Intl.PluralRules constructor has the following properties:

15.3.1 Intl.PluralRules.prototype

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

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

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

The value of the "length" property of the supportedLocalesOf method is 1.

15.3.3 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 « ».

Note 1
Unicode Technical Standard 35 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 http://cldr.unicode.org).

15.4 Properties of the Intl.PluralRules Prototype Object

The Intl.PluralRules prototype object is itself an ordinary object. %PluralRulesPrototype% 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.

15.4.1 Intl.PluralRules.prototype.constructor

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

15.4.2 Intl.PluralRules.prototype [ @@toStringTag ]

The initial value of the @@toStringTag property is the String value "Object".

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

15.4.3 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 ? RequireInternalSlot(pr, [[InitializedPluralRules]]).
  3. Let n be ? ToNumber(value).
  4. Return ? ResolvePlural(pr, n).

15.4.4 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 ? RequireInternalSlot(pr, [[InitializedPluralRules]]).
  3. Let options be ! ObjectCreate(%ObjectPrototype%).
  4. For each row of Table 11, 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 pr's internal slot whose name is the Internal Slot value of the current row.
    3. If v is not undefined, then
      1. Perform ! CreateDataPropertyOrThrow(options, p, v).
  5. Let pluralCategories be a List of Strings representing the possible results of PluralRuleSelect for the selected locale pr.[[Locale]]. This List consists of unique String values, from the the list "zero", "one", "two", "few", "many" and "other", that are relevant for the locale whose localization is specified in LDML Language Plural Rules.
  6. Perform ! CreateDataProperty(options, "pluralCategories", CreateArrayFromList(pluralCategories)).
  7. Return options.
Table 11: Resolved Options of PluralRules Instances
Internal Slot Property
[[Locale]] "locale"
[[Type]] "type"
[[MinimumIntegerDigits]] "minimumIntegerDigits"
[[MinimumFractionDigits]] "minimumFractionDigits"
[[MaximumFractionDigits]] "maximumFractionDigits"
[[MinimumSignificantDigits]] "minimumSignificantDigits"
[[MaximumSignificantDigits]] "maximumSignificantDigits"

15.5 Properties of Intl.PluralRules Instances

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

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

Intl.PluralRules instances also have several internal slots that are computed by the 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.
  • [[MinimumIntegerDigits]] is a non-negative integer Number value indicating the minimum integer digits to be used.
  • [[MinimumFractionDigits]] and [[MaximumFractionDigits]] are non-negative integer Number values 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 Number values indicating the minimum and maximum fraction digits to be used. Either none or both of these properties are present; if they are, they override minimum and maximum integer and fraction digits.
  • [[RoundingType]] is one of the values fractionDigits or significantDigits, indicating which rounding strategy to use, as discussed in 12.5.

16 Locale Sensitive Functions of the ECMAScript Language Specification

The ECMAScript Language Specification, edition 10 or successor, describes several locale sensitive functions. An ECMAScript implementation that implements this Internationalization API 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.

16.1 Properties of the String Prototype Object

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

This definition supersedes the definition provided in ES2020, 21.1.3.10.

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

  1. Let O be RequireObjectCoercible(this value).
  2. Let S be ? ToString(O).
  3. Let thatValue be ? ToString(that).
  4. Let collator be ? Construct(%Collator%, « locales, options »).
  5. Return CompareStrings(collator, S, thatValue).

The value of the "length" property of the localeCompare method is 1.

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.

16.1.2 String.prototype.toLocaleLowerCase ( [ locales ] )

This definition supersedes the definition provided in ES2020, 21.1.3.23.

This function interprets a String value as a sequence of code points, as described in ES2020, 6.1.4. The following steps are taken:

  1. Let O be RequireObjectCoercible(this value).
  2. Let S be ? ToString(O).
  3. Let requestedLocales be ? CanonicalizeLocaleList(locales).
  4. If requestedLocales is not an empty List, then
    1. Let requestedLocale be requestedLocales[0].
  5. Else,
    1. Let requestedLocale be DefaultLocale().
  6. Let noExtensionsLocale be the String value that is requestedLocale with all Unicode locale extension sequences (6.2.1) removed.
  7. Let availableLocales be a List with language tags that includes the languages for which the Unicode Character Database contains language sensitive case mappings. Implementations may add additional language tags if they support case mapping for additional locales.
  8. Let locale be BestAvailableLocale(availableLocales, noExtensionsLocale).
  9. If locale is undefined, let locale be "und".
  10. Let cpList be a List containing in order the code points of S as defined in ES2020, 6.1.4, starting at the first element of S.
  11. Let cuList be a List where the elements are the result of a lower case transformation of the ordered code points in cpList according to the Unicode Default Case Conversion algorithm or an implementation defined conversion algorithm. A conforming implementation's lower case transformation algorithm must always yield the same cpList given the same cuList and locale.
  12. Let L be a String whose elements are the UTF-16 Encoding (defined in ES2020, 6.1.4) of the code points of cuList.
  13. Return L.

Lower case 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 specific tailoring defined in SpecialCasings.txt and/or CLDR and/or any other custom tailoring.

Note 1
The case mapping of some code points may produce multiple code points. In this case the result String may not be the same length as the source String. 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().
Note 2
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.

16.1.3 String.prototype.toLocaleUpperCase ( [ locales ] )

This definition supersedes the definition provided in ES2020, 21.1.3.24.

This function interprets a String value as a sequence of code points, as described in ES2020, 6.1.4. This function behaves in exactly the same way as String.prototype.toLocaleLowerCase, except that characters are mapped to their uppercase equivalents. A conforming implementation's upper case transformation algorithm must always yield the same result given the same sequence of code points and locale.

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.

16.2 Properties of the Number Prototype Object

The following definition(s) refer to the abstract operation thisNumberValue as defined in ES2020, 20.1.3.

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

This definition supersedes the definition provided in ES2020, 20.1.3.4.

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

  1. Let x be ? thisNumberValue(this value).
  2. Let numberFormat be ? Construct(%NumberFormat%, « locales, options »).
  3. Return ? FormatNumeric(numberFormat, x).

16.3 Properties of the BigInt Prototype Object

The following definition(s) refer to the abstract operation thisBigIntValue as defined in ES2020, 20.2.3.

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

This definition supersedes the definition provided in ES2020, 20.2.3.2.

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

  1. Let x be ? thisBigIntValue(this value).
  2. Let numberFormat be ? Construct(%NumberFormat%, « locales, options »).
  3. Return ? FormatNumeric(numberFormat, x).

16.4 Properties of the Date Prototype Object

The following definition(s) refer to the abstract operation thisTimeValue as defined in ES2020, 20.4.4.

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

This definition supersedes the definition provided in ES2020, 20.4.4.39.

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

  1. Let x be ? thisTimeValue(this value).
  2. If x is NaN, return "Invalid Date".
  3. Let options be ? ToDateTimeOptions(options, "any", "all").
  4. Let dateFormat be ? Construct(%DateTimeFormat%, « locales, options »).
  5. Return ? FormatDateTime(dateFormat, x).

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

This definition supersedes the definition provided in ES2020, 20.4.4.38.

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

  1. Let x be ? thisTimeValue(this value).
  2. If x is NaN, return "Invalid Date".
  3. Let options be ? ToDateTimeOptions(options, "date", "date").
  4. Let dateFormat be ? Construct(%DateTimeFormat%, « locales, options »).
  5. Return ? FormatDateTime(dateFormat, x).

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

This definition supersedes the definition provided in ES2020, 20.4.4.40.

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

  1. Let x be ? thisTimeValue(this value).
  2. If x is NaN, return "Invalid Date".
  3. Let options be ? ToDateTimeOptions(options, "time", "time").
  4. Let timeFormat be ? Construct(%DateTimeFormat%, « locales, options »).
  5. Return ? FormatDateTime(timeFormat, x).

16.5 Properties of the Array Prototype Object

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

This definition supersedes the definition provided in ES2020, 22.1.3.29.

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

  1. Let array be ? ToObject(this value).
  2. Let len be ? ToLength(? Get(array, "length")).
  3. Let separator be the String value for the list-separator String appropriate for the host environment's current locale (this is derived in an implementation-defined way).
  4. Let R be the empty String.
  5. Let k be 0.
  6. Repeat, while k < len
    1. If k > 0, then
      1. Set R to the string-concatenation of R and separator.
    2. Let nextElement be ? Get(array, ! ToString(k)).
    3. If nextElement is not undefined or null, then
      1. Let S be ? ToString(? Invoke(nextElement, "toLocaleString", « locales, options »)).
      2. Set R to the string-concatenation of R and S.
    4. Increase k by 1.
  7. Return R.
Note 1
This algorithm's steps mirror the steps taken in 22.1.3.29, with the exception that 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 a separator String that has been derived in an implementationdefined locale-specific way. The result of calling this function is intended to be analogous to the result of toString, except that the result of this function is intended to be locale-specific.
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.

A Implementation Dependent Behaviour

The following aspects of the ECMAScript 2020 Internationalization API Specification are implementation dependent:

  • In all functionality:
  • In Locale:
    • Support for the Unicode extensions keys "kn", "kf" and the parallel options properties "numeric", "caseFirst" (10.1.3)
  • In Collator:
    • Support for the Unicode extensions keys "kn", "kf" and the parallel options properties "numeric", "caseFirst" (11.1.1)
    • The set of supported "co" key values (collations) per locale beyond a default collation (11.2.3)
    • The set of supported "kn" key values (numeric collation) per locale (11.2.3)
    • The set of supported "kf" key values (case order) per locale (11.2.3)
    • The default search sensitivity per locale (11.2.3)
    • The sort order for each supported locale and options combination (11.3.3.1)
  • In NumberFormat:
    • The set of supported "nu" key values (numbering systems) per locale (12.3.3)
    • 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 (12.1.8)
    • Localized representations of NaN and Infinity (12.1.8)
    • The implementation of numbering systems not listed in Table 4 (12.1.8)
    • Localized decimal and grouping separators (12.1.8)
    • Localized plus and minus signs (12.1.8)
    • Localized digit grouping schemata (12.1.8)
    • Localized magnitude thresholds for compact notation (12.1.8)
    • Localized symbols for compact and scientific notation (12.1.8)
    • Localized narrow, short, and long currency symbols and names (12.1.8)
    • Localized narrow, short, and long unit symbols (12.1.8)
  • In DateTimeFormat:
    • The BestFitFormatMatcher algorithm (13.1.1)
    • The set of supported "ca" key values (calendars) per locale (13.3.3)
    • The set of supported "nu" key values (numbering systems) per locale (13.3.3)
    • The default hourCycle setting per locale (13.3.3)
    • The set of supported date-time formats per locale beyond a core set, including the representations used for each component and the associated patterns (13.3.3)
    • Localized weekday names, era names, month names, am/pm indicators, and time zone names (13.1.7)
    • The calendric calculations used for calendars other than "gregory", and adjustments for local time zones and daylight saving time (13.1.7)
  • In RelativeTimeFormat:
    • The set of supported "nu" key values (numbering systems) per locale (14.3.3)
    • The patterns used for formatting values (14.3.3)
  • In PluralRules:
    • List of Strings representing the possible results of plural selection and their corresponding order per locale. (15.1.1)

B Additions and Changes That Introduce Incompatibilities with Prior Editions

  • 11.1, 12.2, 13.2 In ECMA-402, 1st Edition, constructors could be used to create Intl objects from arbitrary objects. This is no longer possible in 2nd Edition.
  • 13.4.3 In ECMA-402, 1st Edition, the "length" property of the function object F was set to 0. In 2nd Edition, "length" is set to 1.

C Colophon

This specification is authored on GitHub in a plaintext source format called Ecmarkup. Ecmarkup is an HTML and Markdown dialect that provides a framework and toolset for authoring ECMAScript specifications in plaintext and processing the specification into a full-featured HTML rendering that follows the editorial conventions for this document. Ecmarkup builds on and integrates a number of other formats and technologies including Grammarkdown for defining syntax and 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.
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