Function IsValidTimeZoneName

packages/ecma402-abstract/IsValidTimeZoneName.ts:57–92

(
  tz: string,
  {
    zoneNamesFromData,
    uppercaseLinks,
  }: {
    zoneNamesFromData: readonly string[]
    uppercaseLinks: Record<string, string>
  }
)

 * @returns true if timeZone is a valid identifier
 */
export function IsValidTimeZoneName(
  tz: string,
  {
    zoneNamesFromData,
    uppercaseLinks,
  }: {
    zoneNamesFromData: readonly string[]
    uppercaseLinks: Record<string, string>
  }
): boolean {
  // 1. If IsTimeZoneOffsetString(timeZone) is true, return true
  // Per ECMA-402 PR #788, UTC offset identifiers are valid
  if (IsTimeZoneOffsetString(tz)) {
    return true
  }

  // 2. Let timeZones be AvailableNamedTimeZoneIdentifiers()
  // 3. If timeZones contains an element equal to timeZone, return true
  // NOTE: Implementation uses case-insensitive comparison per spec note
  const uppercasedTz = tz.toUpperCase()
  const zoneNames = new Set()
  const linkNames = new Set()

  zoneNamesFromData.map(z => z.toUpperCase()).forEach(z => zoneNames.add(z))
  Object.keys(uppercaseLinks).forEach(linkName => {
    linkNames.add(linkName.toUpperCase())
    zoneNames.add(uppercaseLinks[linkName].toUpperCase())
  })

  if (zoneNames.has(uppercasedTz) || linkNames.has(uppercasedTz)) {
    return true
  }

  // 4. Return false
  return false
}