What is the `Intl` namespace object for?

TL;DR

Intl provides locale-aware formatting and comparison for numbers, currencies, dates, times, lists, relative time, plural categories, segments, and more. Pass the locale and domain options explicitly rather than hand-building localized strings. For dates, specify the intended time zone; for money, store the currency separately from the numeric amount. Exact output can vary with locale data, so test semantic parts rather than brittle punctuation where possible.

const date = new Date('2026-08-11T04:00:00Z');
const formatter = new Intl.DateTimeFormat('en-US');
console.log(formatter.format(date)); // Locale-formatted calendar date

What is the `Intl` namespace object for?

The Intl namespace object in JavaScript is a part of the ECMAScript Internationalization API, which provides language-sensitive string comparison, number formatting, and date and time formatting. This is particularly useful for applications that need to support multiple languages and regions.

Language-sensitive string comparison

The Intl.Collator object is used for comparing strings in a locale-aware manner. This is useful for sorting strings in a way that is consistent with the conventions of a particular language.

const collator = new Intl.Collator('de-DE');
console.log(collator.compare('ä', 'z')); // Outputs a negative number because 'ä' comes before 'z' in German

Number formatting

The Intl.NumberFormat object is used for formatting numbers according to the conventions of a specific locale. This includes formatting for currency, percentages, and plain numbers.

const number = 1234567.89;
const formatter = new Intl.NumberFormat('de-DE', {
  style: 'currency',
  currency: 'EUR',
});
console.log(formatter.format(number)); // German-formatted EUR amount

Date and time formatting

The Intl.DateTimeFormat object is used for formatting dates and times according to the conventions of a specific locale.

const date = new Date();
const formatter = new Intl.DateTimeFormat('en-GB', {
  year: 'numeric',
  month: 'long',
  day: 'numeric',
});
console.log(formatter.format(date)); // British English long date

Plural rules

The Intl.PluralRules object is used to get the plural form of a number in a specific locale. This is useful for correctly pluralizing words in different languages.

const pluralRules = new Intl.PluralRules('en-US');
console.log(pluralRules.select(1)); // Outputs 'one'
console.log(pluralRules.select(2)); // Outputs 'other'

Intl.PluralRules returns a category; the application still provides translated message forms. English-style count === 1 ? singular : plural logic does not generalize to every language.

Practical considerations

const formatter = new Intl.DateTimeFormat('en-GB', {
  dateStyle: 'medium',
  timeStyle: 'short',
  timeZone: 'Asia/Singapore',
});

console.log(formatter.format(new Date('2026-08-11T04:00:00Z')));

Reuse a formatter when formatting many values instead of constructing one for every table cell.
Use formatToParts() when markup must wrap specific semantic pieces; do not split a formatted string on assumed punctuation.
Locale fallback and supported options depend on the runtime's locale data. Use supportedLocalesOf() when exact locale support matters.
Intl formats values but does not translate arbitrary product copy or convert time zones into business-calendar rules.

Exercícios

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What is the `Intl` namespace object for?

TL;DR