Function CanonicalizeLocaleList

packages/intl-getcanonicallocales/index.ts:29–90

* https://tc39.es/ecma402/#sec-canonicalizelocalelist * @param locales

(
  locales?:
    | string[]
    | string
    | Intl.Locale
    | Intl.Locale[]
    | ArrayLike<string | Intl.Locale>
)

 * @param locales
 */
function CanonicalizeLocaleList(
  locales?:
    | string[]
    | string
    | Intl.Locale
    | Intl.Locale[]
    | ArrayLike<string | Intl.Locale>
): string[] {
  // Step 1-2: If locales is undefined, return empty list
  if (locales === undefined) {
    return []
  }

  const seen: string[] = []

  // Step 3-4: Handle string or Locale object by wrapping in array
  // Per spec: "If Type(locales) is String or Type(locales) is Object and locales has an
  // [[InitializedLocale]] internal slot, then Let O be CreateArrayFromList(« locales »)"
  if (typeof locales === 'string' || isLocaleObject(locales)) {
    locales = [locales as string | Intl.Locale]
  }

  // Step 5-6: Convert to object and get length for array-like objects
  // Per spec: "Let O be ? ToObject(locales)" and "Let len be ? ToLength(? Get(O, "length"))"
  const O = Object(locales)
  const len = typeof O.length === 'number' ? O.length : 0

  // Step 7: Iterate through elements
  for (let k = 0; k < len; k++) {
    // Check if property exists
    if (!(k in O)) {
      continue
    }

    const kValue = O[k]

    // Step 7c-d: Extract locale string
    let tag: string
    if (typeof kValue === 'string') {
      tag = kValue
    } else if (isLocaleObject(kValue)) {
      // For Intl.Locale objects, use toString() which returns the canonicalized locale
      tag = kValue.toString()
    } else {
      throw new TypeError(
        `Invalid locale type: expected string or Intl.Locale, got ${typeof kValue}`
      )
    }

    // Step 7e-g: Validate and canonicalize
    const canonicalizedTag = emitUnicodeLocaleId(
      CanonicalizeUnicodeLocaleId(parseUnicodeLocaleId(tag))
    )

    // Step 7h: Deduplicate
    if (seen.indexOf(canonicalizedTag) < 0) {
      seen.push(canonicalizedTag)
    }