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Match BCP 47 language tags with language ranges per RFC 4647
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bcp-47-match

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Match BCP 47 language tags with “language ranges” per RFC 4647, as done by the :lang() pseudo-class in CSS, or the Accept-Language HTTP header.

Related to bcp-47.

Installation

npm:

npm install bcp-47-match

Table of Contents

Usage

var match = require('bcp-47-match')

var basic = match.basicFilter
var extended = match.extendedFilter
var lookup = match.lookup

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

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

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

API

match.basicFilter(tags[, ranges])

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.

View matching table
Basic Filter * de de-CH de-DE de-*-DE *-CH
de ✔︎ ✔︎
de-CH ✔︎ ✔︎ ✔︎
de-CH-1996 ✔︎ ✔︎ ✔︎
de-DE ✔︎ ✔︎ ✔︎
de-DE-1996 ✔︎ ✔︎ ✔︎
de-DE-x-goethe ✔︎ ✔︎ ✔︎
de-Deva ✔︎ ✔︎
de-Deva-DE ✔︎ ✔︎
de-Latf-DE ✔︎ ✔︎
de-Latn-DE ✔︎ ✔︎
de-Latn-DE-1996 ✔︎ ✔︎
de-x-DE ✔︎ ✔︎
en ✔︎
en-GB ✔︎
zh ✔︎
zh-Hans ✔︎
zh-Hant ✔︎
Parameters
  • tags (string or Array.<string>) — List of BCP-47 tags
  • ranges (string or Array.<string>) — List of RFC 4647 basic ranges (aka, matching /^(\*|[a-z]{1,8}(-[a-z0-9]{1,8})*)$/i)
Returns

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

match.extendedFilter(tags[, ranges])

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.

View matching table
Extended Filter * de de-CH de-DE de-*-DE *-CH
de ✔︎ ✔︎
de-CH ✔︎ ✔︎ ✔︎ ✔︎
de-CH-1996 ✔︎ ✔︎ ✔︎ ✔︎
de-DE ✔︎ ✔︎ ✔︎ ✔︎
de-DE-1996 ✔︎ ✔︎ ✔︎ ✔︎
de-DE-x-goethe ✔︎ ✔︎ ✔︎ ✔︎
de-Deva ✔︎ ✔︎
de-Deva-DE ✔︎ ✔︎ ✔︎ ✔︎
de-Latf-DE ✔︎ ✔︎ ✔︎ ✔︎
de-Latn-DE ✔︎ ✔︎ ✔︎ ✔︎
de-Latn-DE-1996 ✔︎ ✔︎ ✔︎ ✔︎
de-x-DE ✔︎ ✔︎
en ✔︎
en-GB ✔︎
zh ✔︎
zh-Hans ✔︎
zh-Hant ✔︎
Parameters
  • tags (string or Array.<string>) — List of BCP-47 tags
  • ranges (string or Array.<string>) — List of RFC 4647 extended ranges (aka, matching /^(\*|[a-z]{1,8})(-(\*|[a-z0-9]{1,8}))*$/i)
Returns

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

match.lookup(tags, ranges)

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.

View matching table
Lookup * de de-CH de-DE de-*-DE *-CH
de ✔︎︎ ✔︎︎ ✔︎ ✔︎ ✔︎
de-CH ✔︎ ✔︎
de-CH-1996 ✔︎
de-DE ✔︎ ✔︎
de-DE-1996 ✔︎
de-DE-x-goethe ✔︎
de-Deva ✔︎
de-Deva-DE ✔︎
de-Latf-DE ✔︎
de-Latn-DE ✔︎
de-Latn-DE-1996 ✔︎
de-x-DE ✔︎
en ✔︎
en-GB ✔︎
zh ✔︎
zh-Hans ✔︎
zh-Hant ✔︎
Parameters
  • tags (string or Array.<string>) — List of BCP-47 tags
  • ranges (string or Array.<string>) — List of RFC 4647 basic ranges (but * is ignored)
Returns

string? — The first matching tag in tags, or undefined otherwise.

License

MIT © Titus Wormer

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