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Intl Formatting ​

The intl getter on LocaleManager provides cached Intl.NumberFormat, Intl.DateTimeFormat, and Intl.RelativeTimeFormat instances tied to the current locale. Formatters are cached for performance and the cache is intentionally retained across locale changes so switching back to a previous locale is instant.

intl.number() ​

Format numbers with locale-aware grouping, currency, and percentage styles.

ts
i18n.intl.number(1499.99);
// "1,499.99"

i18n.intl.number(9.99, { style: 'currency', currency: 'USD' });
// "$9.99"

i18n.intl.number(0.15, { style: 'percent' });
// "15%"

After switching locales, the same calls produce locale-appropriate output:

ts
await i18n.changeTo('de');

i18n.intl.number(1499.99);
// "1.499,99"

i18n.intl.number(9.99, { style: 'currency', currency: 'EUR' });
// "9,99 €"

intl.date() ​

Format dates with predefined styles or custom options.

ts
i18n.intl.date(new Date());
// "2/18/2026"

i18n.intl.date(new Date(), { dateStyle: 'full' });
// "Wednesday, February 18, 2026"

i18n.intl.date(new Date(), { year: 'numeric', month: 'long' });
// "February 2026"
ts
await i18n.changeTo('es');

i18n.intl.date(new Date(), { dateStyle: 'full' });
// "miércoles, 18 de febrero de 2026"

intl.relative() ​

Format relative time with various units.

ts
i18n.intl.relative(-3, 'day');
// "3 days ago"

i18n.intl.relative(1, 'hour');
// "in 1 hour"

i18n.intl.relative(-1, 'month');
// "1 month ago"

i18n.intl.relative(2, 'week');
// "in 2 weeks"

createIntlFormatters() Standalone Factory ​

The createIntlFormatters function is exported for use outside of LocaleManager. It creates a formatters object for a given locale code without needing a manager instance.

ts
import { createIntlFormatters } from '@logosdx/localize';

const fmt = createIntlFormatters('ja');

fmt.number(1499.99);
// "1,499.99" (Japanese locale grouping)

fmt.date(new Date(), { dateStyle: 'long' });
// "2026年2月18日"

fmt.relative(-1, 'day');
// "1 日前"

Caching Behavior ​

Performance

Formatter instances are cached globally by locale + options combination. The cache is intentionally retained across locale changes. Typical applications use a small number of locales, so the memory cost is negligible and switching back to a previously-used locale is instant.

When the locale changes via changeTo(), the intl getter on the manager resets its reference so it creates formatters for the new locale. But previously-created formatters for other locales remain in the global cache and are reused if you switch back.

ts
// First time — creates and caches formatters for 'en'
i18n.intl.number(42);

await i18n.changeTo('es');
// Creates and caches formatters for 'es'
i18n.intl.number(42);

await i18n.changeTo('en');
// Reuses cached formatters for 'en' — no new Intl objects created
i18n.intl.number(42);