createLocalePath

URL maths for a multilingual site. Pure functions, no global state, no DOM — usable in a build script (sitemap, hreflang) and in the browser alike.

Uses sub-directories (/zh/book/) rather than sub-domains (zh.example.com/book/): search engines treat a sub-domain as a separate site whose authority starts from zero, while a sub-directory inherits the main site's. The default locale lives at the root; every other locale carries a prefix.

API

createLocalePath(config)

Parameter	Description	Type	Default
`locales`	`{ code, prefix? }[]`; no prefix means "default locale, lives at root"	`LocaleRoute[]`	Required
`defaultLocale`	Default locale code	`string`	first prefix-less
`base`	Deployment sub-path, e.g. `/weread`; trailing slash is ignored	`string`	`''`

Returns:

Member	Description
`base` / `defaultLocale`	Normalized config, read-only
`localeFromPath(pathname)`	Detect the locale; unknown paths fall back to the default
`stripLocale(pathname)`	Drop the locale prefix: the language-agnostic path for routing
`href(path, code?)`	Build a link for a locale
`hrefForLocale(pathname, code)`	Re-point the current path at another locale (language switcher)
`alternates(pathname)`	Every locale's URL, for `<link rel="alternate" hreflang>`

Example

import { createLocalePath } from 'ranuts';

const paths = createLocalePath({
  locales: [{ code: 'en' }, { code: 'zh-CN', prefix: 'zh' }, { code: 'zh-HK', prefix: 'zh-hant' }],
  base: '/docs',
});

paths.href('/book/walden/'); // '/docs/book/walden/'
paths.href('/book/walden/', 'zh-CN'); // '/docs/zh/book/walden/'
paths.localeFromPath('/docs/zh/book/'); // 'zh-CN'
paths.stripLocale('/docs/zh/book/'); // '/docs/book/'
paths.hrefForLocale('/docs/zh/book/', 'zh-HK'); // '/docs/zh-hant/book/'

// hreflang tags
paths.alternates(location.pathname).forEach(({ code, href }) => {
  head.append(link({ rel: 'alternate', hreflang: code, href }));
});

Notes

href is idempotent. It strips any existing prefix before adding the new one, so feeding it an already-localized path does not double up — and hrefForLocale is just href.
Longest prefix wins, so zh does not swallow /zh-hant/....
base is only stripped from the start. Using replace(base, '') would strip the first occurrence anywhere, which breaks when the path contains the base string mid-way.
Query and hash are preserved: the maths only touches the pathname.
No global "current locale". Pass the code explicitly, or default it. Which locale is active is the i18n runtime's job, not this module's.