Proposal for Intl.DurationFormat

Stage: 2

Champion: Younies Mahmoud, Ujjwal Sharma

Authors: Younies Mahmoud, Ujjwal Sharma

Stage 3 Reviewers



This proposal reached Stage 1 at the 2020 Feb TC39 meeting. This proposal reached Stage 2 at the 2020 June TC39 meeting.


  • Time Duration is how long something lasts, from the start to end. It can be represented by a single time unit or multiple ones.
    • For example,
      • 10000 seconds
      • 2 hours 46 minutes 40 seconds
  • Every locale has its own way to format duration.
    • For example:
      • en-US: 1 hour, 46 minutes and 40 seconds
      • fr-FR: 1 heure, 46 minutes et 40 secondes
  • There are multiple widths for the time duration.
    • For example, wide and short
      • 1 hour, 46 minutes and 40 seconds → Wide
      • 1 hr, 46 min, 40 sec → Short

Quick Start

new Intl.DurationFormat("fr-FR", { style: "long" }).format({
    hours: 1,
    minutes: 46,
    seconds: 40,
// => "1 heure, 46 minutes et 40 secondes"


  • Users need all types of duration formatting depending on the requirements of their application. For example, to show how long a flight takes, the duration should be in Short or Narrow format
    • "1 hr 40 min 60 sec" → Short
    • "1h 40m 60s" → Narrow

Requirements & Design

In this section, we are going to illustrate each user needs (requirements) and a design for each need (requirement)

Input Value

  • Users need to identify how to input a duration value. For example, if a user needs to format 1000 seconds , how could the user pass the value to the formatting function.


  • Input value will be an object of type Temporal.Duration
  • Example: new DurationFormat().format(Temporal.Duration.from({hours: 3, minutes: 4});

Formatting width

Users want to determine several types of the formatting width as following

Format width Example
Long 1 hour and 50 minutes
Short 1 hr, 50 min
Narrow 1h 50m
Digital 1:50:00


  • The user can determine the formatting width using a parameter style and the value of this parameter may be one of the following strings:
    • "long"
    • "short"
    • "narrow"
    • "digital"
  • The width of each field can be set separately in the options, for example: { years: "long", months: "short", days: "narrow" }.

Supported Duration Units

  • Users need the following fields to be supported
    • Years
    • Months
    • Weeks
    • Days
    • Hours
    • Minutes
    • Seconds
    • Milliseconds
    • Microseconds
    • Nanoseconds


  • We are going to support the same fields as in Temporal.Duration , which contains:
    • years
    • months
    • weeks
    • days
    • hours
    • minutes
    • seconds
    • milliseconds
    • microseconds
    • nanoseconds

Determining Duration Units

DurationFormat does not do any arithmetic operations nor rounding on the input implicitly. Instead, the user must edit the input (e.g. using Temporal.Duration.prototype.round) to ensure the input is within the desired range.

To avoid accidentally omitting part of the duration, DurationFormat always outputs all nonzero fields (except sub-second fields truncated by fractionalDigits). Callers who want to omit nonzero fields (for example, only showing the date or time portion of the duration) should edit the input duration.


  • Users can determine the time fields in array.
  • Example:
    fields: [

Hide zero-value fields

In most cases, users want to avoid displaying zero-value fields. All zero-valued fields are hidden by default. If you specify the style for a specific field, then it is always displayed, but you can override that behavior by also setting the display option for that particular field to "auto" again explicitly.


For each field foo, there is an option fooDisplay that is set to "auto" by default. Setting that option to "always" causes that field to be displayed even if it is zero; for example, to always show the "day" field, set { dayDisplay: "always" }. If you specify the style for that field by setting the foo option, then the default for fooDisplay becomes "always"; for example, { day: "short" } implies { day: "short", dayDisplay: "always" }.


  • Users wants to decide if they are going to round the smallest field or not.
  • for example:
    • Without rounding option
      • 1 hour and 30.6 minutes.
    • With rounding option
      • 1 hour and 31 minutes.


  • Users could use Temporal.Duration#round function.

Locale-aware format

  • Users needs the formatting to be dependent on the locale
  • For example:
    • en-US
      • 1 hour, 46 minutes and 40 seconds
    • fr-FR
      • 1 heure, 46 minutes et 40 secondes


Adding the locale in string format as a first argument, or specifying a ranked list of locales as an array of string locale values.

Display fractional values

Sometimes it is desirable to display the smallest sub-second unit not by itself but as a fraction of the immediately larger unit.


We allow users to specify a fractionalDigits option that will display the smallest sub-second unit with display set to "auto" as a fraction of the previous unit if it is non-zero. The number of digits used will be the value passed to this option.


new Intl.DurationFormat('en', { fractionalDigits: 2 }).format('PT12.3456S'); // => 12.34 sec
new Intl.DurationFormat('en', { milliseconds: 'narrow', fractionalDigits: 2 }).format('PT12.3456S'); // => 12s 345.60ms

API design

    new Intl.DurationFormat('en').format(Temporal.Duration.from('PT2H46M40S')); // => 2 hr 46 min 40 sec
    new Intl.DurationFormat('en', {
      hours: 'numeric',
      seconds: 'numeric',
    }).format(Temporal.Duration.from('PT2H40S')); // => 2:00:40



new Intl.DurationFormat(locales, options)


  • locales: Array<string> | string: A locale string or a list of locale strings in decreasing order of preference.
  • options?: object: An object for configuring the behavior of the instance. It may have some or all of the following properties:
    • localeMatcher: "best-fit" | "lookup": A string denoting which locale matching algorithm to use. Defaults to "best fit".
    • numberingSystem: string: A string containing the name of the numbering system to be used for number formatting.
    • style: "long" | "short" | "narrow" | "digital": The base style to be used for formatting. This can be overriden per-unit by setting the more granular options. Defaults to "short".
    • years: "long" | "short" | "narrow": The style to be used for formatting years.
    • yearsDisplay: "always" | "auto": Whether to always display years, or only if nonzero.
    • months: "long" | "short" | "narrow": The style to be used for formatting months.
    • monthsDisplay: "always" | "auto": Whether to always display months, or only if nonzero.
    • weeks: "long" | "short" | "narrow": The style to be used for formatting weeks.
    • weeksDisplay: "always" | "auto": Whether to always display weeks, or only if nonzero.
    • days: "long" | "short" | "narrow": The style to be used for formatting days.
    • daysDisplay: "always" | "auto": Whether to always display days, or only if nonzero.
    • hours: "long" | "short" | "narrow" | "numeric" | "2-digit": The style to be used for formatting hours.
    • hoursDisplay: "always" | "auto": Whether to always display hours, or only if nonzero.
    • minutes: "long" | "short" | "narrow" | "numeric" | "2-digit": The style to be used for formatting minutes.
    • minutesDisplay: "always" | "auto": Whether to always display minutes, or only if nonzero.
    • seconds: "long" | "short" | "narrow" | "numeric" | "2-digit": The style to be used for formatting seconds.
    • secondsDisplay: "always" | "auto": Whether to always display seconds, or only if nonzero.
    • milliseconds: "long" | "short" | "narrow" | "numeric": The style to be used for formatting milliseconds.
    • millisecondsDisplay: "always" | "auto": Whether to always display milliseconds, or only if nonzero.
    • microseconds: "long" | "short" | "narrow" | "numeric": The style to be used for formatting microseconds.
    • microsecondsDisplay: "always" | "auto": Whether to always display microseconds, or only if nonzero.
    • nanoseconds: "long" | "short" | "narrow" | "numeric": The style to be used for formatting nanoseconds.
    • nanosecondsDisplay: "always" | "auto": Whether to always display nanoseconds, or only if nonzero.
    • fractionalDigits: number: How many fractional digits to display in the output. Additional decimal places will be truncated towards zero. (Temporal.Duration.prototype.round can be used to obtain different rounding behavior.) Normally this option applies to fractional seconds, but this option actually applies to the largest seconds-or-smaller unit that uses the "numeric" or "2-digit" style. For example, if options are { seconds: "narrow", milliseconds: "narrow", fractionalDigits: 2} then the output can be "5s 2.39ms". If this option is omitted, only nonzero decimals will be displayed and trailing zeroes will be omitted.
Default values
  • The per-unit style options default to the value of style for all styles except "digital", for which units years till days default to "narrow" and hours till nanoseconds default to "numeric".
  • The per-unit display options default to "auto" if the corresponding style option is undefined and "always" otherwise.


  • Some locales may share the same representation between "long" and "short" or between "narrow" and "short". Others may use different representations for each one, e.g. "3 seconds", "3 secs", "3s".
  • Any unit with the style "numeric" preceded by a unit of style "numeric" or "2-digit" should act like the style "2-digit" was used instead. For example, {hours: 'numeric', minutes: 'numeric'} can produce output like "3:08".



new Intl.DurationFormat('en').format(duration)


  • duration (Temporal.Duration | string | object): The duration to be formatted. This could either be a Temporal.Duration object or a string or options bag that can be converted into one.


A string containing the formatted duration.



new Intl.DurationFormat('en').formatToParts(duration)


  • duration (Temporal.Duration | string | object): The duration to be formatted. This could either be a Temporal.Duration object or a string or options bag that can be converted into one.


An Array<{type: string, value: string}> containing the formatted duration in parts.

Implementation Status

V8 Prototypes

Three v8 prototypes (try to use two different possible ICU classes) were made, ALL are:

  1. Base the implementation on icu::MeasureFormat::formatMeasures()
  2. Based on the support of "-and-" unit in LocalizedNumberFormatter
  3. Based on icu::ListFormatter and icu::number::LocalizedNumberFormatter w/o depend on the "X-and-Y" units.