subtag.js

!function(root, name, make) {
  if (typeof module != 'undefined' && module.exports) module.exports = make()
  else root[name] = make()
}(this, 'subtag', function() {

  var empty = ''
  var pattern = /^([a-zA-Z]{2,3})(?:[_-]+([a-zA-Z]{3})(?=$|[_-]+))?(?:[_-]+([a-zA-Z]{4})(?=$|[_-]+))?(?:[_-]+([a-zA-Z]{2}|[0-9]{3})(?=$|[_-]+))?/

  function match(tag) {
    return tag.match(pattern) || []
  }

  function split(tag) {
    return match(tag).filter(function(v, i) { return v && i })
  }

  function api(tag) {
    tag = match(tag)
    return {
      language: tag[1] || empty,
      extlang: tag[2] || empty,
      script: tag[3] || empty,
      region: tag[4] || empty
    }
  }

  function expose(target, key, value) {
    Object.defineProperty(target, key, {
      value: value,
      enumerable: true
    })
  }

  function part(position, pattern, type) {
    function method(tag) {
      return match(tag)[position] || empty
    }
    expose(method, 'pattern', pattern)
    expose(api, type, method)
  }

  part(1, /^[a-zA-Z]{2,3}$/, 'language')
  part(2, /^[a-zA-Z]{3}$/, 'extlang')
  part(3, /^[a-zA-Z]{4}$/, 'script')
  part(4, /^[a-zA-Z]{2}$|^[0-9]{3}$/, 'region')

  expose(api, 'split', split)

  return api
});