`direction.ts` — text-direction helpers

(no submodules)

Purpose

getTextDirection(locale) and isRtl(locale) resolve a locale's display direction without instantiating a full locale resolver or booting the slim core. They are pure functions over RTL_LOCALES from @suaveplan/i18n-shared and complete in O(1) — perfect for use in render hot paths (e.g. <html dir={getTextDirection(locale)}>) where every microsecond saved compounds across SSR fan-out.

The helpers ship in @suaveplan/i18n-detector rather than the slim core because direction lookup is logically part of the locale- resolution surface — every consumer that detects a locale needs to know which direction to render — and pulling them here keeps the slim core lighter.

Features

getTextDirection(locale) returns "ltr" or "rtl" for any BCP-47 locale tag.
isRtl(locale) is sugar for getTextDirection(locale) === "rtl".
Region subtags are tolerated: "ar-SA", "he-IL", "fa-IR" all resolve to "rtl".
Lookup is case-insensitive — the language subtag is lower-cased before the RTL_LOCALES set probe.
Unknown locales default to "ltr", matching browser behaviour.

Usage: Basic Example

import { getTextDirection, isRtl } from "@suaveplan/i18n-detector/direction";

getTextDirection("ar"); // "rtl"
getTextDirection("ar-SA"); // "rtl"
getTextDirection("en-GB"); // "ltr"
isRtl("he-IL"); // true

Usage: Advanced Example

import { getTextDirection } from "@suaveplan/i18n-detector/direction";

export function HtmlShell({
    locale,
    children,
}: {
    locale: string;
    children: React.ReactNode;
}) {
    return (
        <html lang={locale} dir={getTextDirection(locale)}>
            {children}
        </html>
    );
}

API Reference

getTextDirection(locale: string): "ltr" | "rtl" — pure.
isRtl(locale: string): boolean — pure.
type TextDirection = "ltr" | "rtl" — re-exported for consumer type-safety.

Implementation Notes

The language subtag is everything before the first -. Multi-tag locales (zh-Hant-TW) resolve via the first segment only — script subtags are ignored because every script-bearing RTL locale is already covered by its language subtag.
Adding a new RTL language is a one-line change in @suaveplan/i18n-shared/constants/rtl-locales.ts — no detector code needs to be touched.

2.4 KiB Raw Blame History

direction.ts — text-direction helpers