client-side module to get Keen.io-compatible timezone string

keen-timezone.js

var keenTimezone = function() {
  var
    jan = new Date(now.getFullYear(), 0, 1),
    jul = new Date(now.getFullYear(), 6, 1),
    now = new Date(),
    tzOffset = Math.max(jan.getTimezoneOffset(), jul.getTimezoneOffset()) * -1 / 60,
    dstTzOffset= now.getTimezoneOffset() * -1 / 60,
    offsetsAre = function(expTzOffset, expDstTzOffset) {
      if (tzOffset === expTzOffset && dstTzOffset === expDstTzOffset) {
        return true
      }
      return false
    }
    ;

  if (offsetsAre(-10, -10)) {
    return 'US/Hawaii'
  }
  if (offsetsAre(-9, -8)) {
    return 'US/Alaska'
  }
  if (offsetsAre(-8, -7)) {
    return 'US/Pacific'
  }
  if (offsetsAre(-7, -6)) {
    return 'US/Mountain'
  }
  if (offsetsAre(-6, -5)) {
    return 'US/Central'
  }
  if (offsetsAre(-5, -4)) {
    return 'US/Eastern'
  }
  if (offsetsAre(-3, -2)) {
    return 'America/Sao_Paulo'
  }
  if (offsetsAre(0, 0)) {
    return 'UTC'
  }
  if (offsetsAre(0, 1)) {
    return 'Africa/Casablanca'
  }
  if (offsetsAre(0, 1)) {
    return 'Europe/London'
  }
  if (offsetsAre(1, 2)) {
    return 'Europe/Amsterdam'
  }
  if (offsetsAre(1, 2)) {
    return 'Europe/Paris'
  }
  if (offsetsAre(1, 2)) {
    return 'Europe/Prague'
  }
  if (offsetsAre(1, 2)) {
    return 'Europe/Stockholm'
  }
  if (offsetsAre(1, 2)) {
    return 'Europe/Copenhagen'
  }
  if (offsetsAre(2, 3)) {
    return 'Asia/Istanbul'
  }
  if (offsetsAre(2, 3)) {
    return 'Europe/Istanbul'
  }
  if (offsetsAre(3, 3)) {
    return 'Africa/Nairobi'
  }
  if (offsetsAre(4, 4)) {
    return 'Asia/Dubai'
  }
  if (offsetsAre(7, 7)) {
    return 'Asia/Jakarta'
  }
  if (offsetsAre(8, 8)) {
    return 'Asia/Singapore'
  }
  if (offsetsAre(9, 9)) {
    return 'Asia/Tokyo'
  }
  if (offsetsAre(8, 8)) {
    return 'Australia/Perth'
  }
  if (offsetsAre(10, 11)) {
    return 'Australia/Sydney'
  }
  if (offsetsAre(12, 13)) {
    return 'Pacific/Auckland'
  }
  throw new Error('Unsupported Timezone')
}

module.exports = keenTimezone