Match BCP 47 language tags with language ranges per RFC 4647.

• What is this?
• When should I use this?
• Install
• Use
• API
  • basicFilter(tags[, ranges='*'])
  • extendedFilter(tags[, ranges='*'])
  • lookup(tags, ranges)
• Types
• Compatibility
• Security
• Related
• Contribute
• License

This package can match BCP 47 language tags with “language ranges” per RFC 4647. This is done by the :lang() pseudo class in CSS, the Accept-Language HTTP header, and a few other places.

You can use this package if you want to choose a certain document based on language tags.

This package is ESM only. In Node.js (version 14.14+, 16.0+), install with npm:

npm install bcp-47-match

In Deno with esm.sh:

import * as bcp47Match from 'https://esm.sh/bcp-47-match@2'

In browsers with esm.sh:

<script type="module">
  import * as bcp47Match from 'https://esm.sh/bcp-47-match@2?bundle'
</script>

import {basicFilter, extendedFilter, lookup} from 'bcp-47-match'

const tags = ['en-GB', 'de-CH', 'en', 'de']

console.log(basicFilter(tags, '*')) // => [ 'en-GB', 'de-CH', 'en', 'de' ]
console.log(basicFilter(tags, 'en')) // => [ 'en-GB', 'en' ]
console.log(basicFilter(tags, 'en-GB')) // => [ 'en-GB' ]
console.log(basicFilter(tags, ['en-GB', 'en'])) // => [ 'en-GB', 'en' ]
console.log(basicFilter(tags, 'jp')) // => []

console.log(extendedFilter(tags, '*')) // => [ 'en-GB', 'de-CH', 'en', 'de' ]
console.log(extendedFilter(tags, 'en')) // => [ 'en-GB', 'en' ]
console.log(extendedFilter(tags, 'en-GB')) // => [ 'en-GB' ]
console.log(extendedFilter(tags, '*-GB')) // => [ 'en-GB' ]
console.log(extendedFilter(tags, ['en-GB', 'en'])) // => [ 'en-GB', 'en' ]
console.log(extendedFilter(tags, 'jp')) // => []

console.log(lookup(tags, 'en')) // => 'en'
console.log(lookup(tags, 'en-GB')) // => 'en-GB'
console.log(lookup(tags, ['en-GB', 'en'])) // => 'en-GB'
console.log(lookup(tags, ['en', 'en-GB'])) // => 'en'
console.log(lookup(tags, 'jp')) // => undefined

This package exports the identifier basicFilter, extendedFilter, and lookup. There is no default export.

👉 Note: See Basic Filtering spec

Match language tags to a list of simple ranges. Searches for matches between the first range and all tags, and continues with further ranges. Returns a list of matching tags in the order they matched.

• tags (string or Array<string>) — list of BCP 47 tags
• ranges (string or Array<string>, default: '*') — list of RFC 4647 basic ranges (aka, matching /^(\*|[a-z]{1,8}(-[a-z0-9]{1,8})*)$/i)

Possibly empty list of matching tags in the order they matched (Array<string>).

👉 Note: See Extended Filtering spec

Match language tags to a list of extended ranges. Searches for matches between the first range and all tags, and continues with further ranges.

• tags (string or Array<string>) — list of BCP 47 tags
• ranges (string or Array<string>, default: '*') — list of RFC 4647 extended ranges (aka, matching /^(\*|[a-z]{1,8})(-(\*|[a-z0-9]{1,8}))*$/i)

Possibly empty list of matching tags in the order they matched (Array<string>).

👉 Note: See Lookup spec

Find the best language tag that matches a list of ranges. Searches for a match between the first range and all tags, and continues with further ranges. Returns the first match, if any.

• tags (string or Array<string>) — list of BCP 47 tags
• ranges (string or Array<string>) — list of RFC 4647 basic ranges (but * is ignored)

First matching tag in tags, undefined otherwise (string?).

This package is fully typed with TypeScript. It exports no additional types.

This package is at least compatible with all maintained versions of Node.js. As of now, that is Node.js 14.14+ and 16.0+. It also works in Deno and modern browsers.

This package is safe.

• wooorm/bcp-47 — parse and serialize BCP 47 language tags
• wooorm/bcp-47-normalize — normalize, canonicalize, and format BCP 47 tags
• wooorm/iso-3166 — ISO 3166 codes
• wooorm/iso-639-2 — ISO 639-2 codes
• wooorm/iso-639-3 — ISO 639-3 codes
• wooorm/iso-15924 — ISO 15924 codes
• wooorm/un-m49 — UN M49 codes

Yes please! See How to Contribute to Open Source.

MIT © Titus Wormer