Add getTimezoneOffsetInMilliseconds utility function (#789)

CHANGELOG.md

@@ -639,6 +639,9 @@ for the list of changes made since `v2.0.0-alpha.1`.
 
 - `isDate` now works properly with dates passed across iframes [#754](https://github.com/date-fns/date-fns/pull/754).
 
+- Fix a few bugs that appear in timezones with offsets that include seconds (e.g. GMT+00:57:44).
+  See PR [#789](https://github.com/date-fns/date-fns/pull/789).
+
 ## [1.28.5] - 2017-05-19
 
 ### Fixed

src/_lib/getTimezoneOffsetInMilliseconds/index.js

@@ -0,0 +1,21 @@
+var MILLISECONDS_IN_MINUTE = 60000
+
+/**
+ * Google Chrome as of 67.0.3396.87 introduced timezones with offset that includes seconds.
+ * They usually appear for dates that denote time before the timezones were introduced
+ * (e.g. for 'Europe/Prague' timezone the offset is GMT+00:57:44 before 1 October 1891
+ * and GMT+01:00:00 after that date)
+ *
+ * Date#getTimezoneOffset returns the offset in minutes and would return 57 for the example above,
+ * which would lead to incorrect calculations.
+ *
+ * This function returns the timezone offset in milliseconds that takes seconds in account.
+ */
+export default function getTimezoneOffsetInMilliseconds (dirtyDate) {
+  var date = new Date(dirtyDate.getTime())
+  var baseTimezoneOffset = date.getTimezoneOffset()
+  date.setSeconds(0, 0)
+  var millisecondsPartOfTimezoneOffset = date.getTime() % MILLISECONDS_IN_MINUTE
+
+  return baseTimezoneOffset * MILLISECONDS_IN_MINUTE + millisecondsPartOfTimezoneOffset
+}

src/_lib/getTimezoneOffsetInMilliseconds/test.js

@@ -0,0 +1,28 @@
+// @flow
+/* eslint-env mocha */
+
+import assert from 'power-assert'
+import getTimezoneOffsetInMilliseconds from '.'
+
+describe('getTimezoneOffsetInMilliseconds', function () {
+  it('works for a modern date', function () {
+    var date = new Date(2018, 0 /* Jan */, 1, 12, 34, 56, 789)
+    var result = date.getTime() - getTimezoneOffsetInMilliseconds(date)
+    var expectedResult = Date.UTC(2018, 0 /* Jan */, 1, 12, 34, 56, 789)
+    assert(result === expectedResult)
+  })
+
+  it('works for a date before standardized timezones', function () {
+    var date = new Date(1800, 0 /* Jan */, 1, 12, 34, 56, 789)
+    var result = date.getTime() - getTimezoneOffsetInMilliseconds(date)
+    var expectedResult = Date.UTC(1800, 0 /* Jan */, 1, 12, 34, 56, 789)
+    assert(result === expectedResult)
+  })
+
+  it('works for a date BC', function () {
+    var date = new Date(-500, 0 /* Jan */, 1, 12, 34, 56, 789)
+    var result = date.getTime() - getTimezoneOffsetInMilliseconds(date)
+    var expectedResult = Date.UTC(-500, 0 /* Jan */, 1, 12, 34, 56, 789)
+    assert(result === expectedResult)
+  })
+})

src/differenceInCalendarDays/index.js

@@ -1,6 +1,6 @@
+import getTimezoneOffsetInMilliseconds from '../_lib/getTimezoneOffsetInMilliseconds/index.js'
 import startOfDay from '../startOfDay/index.js'
 
-var MILLISECONDS_IN_MINUTE = 60000
 var MILLISECONDS_IN_DAY = 86400000
 
 /**
@@ -45,9 +45,9 @@ export default function differenceInCalendarDays (dirtyDateLeft, dirtyDateRight,
   var startOfDayRight = startOfDay(dirtyDateRight, dirtyOptions)
 
   var timestampLeft = startOfDayLeft.getTime() -
-    startOfDayLeft.getTimezoneOffset() * MILLISECONDS_IN_MINUTE
+    getTimezoneOffsetInMilliseconds(startOfDayLeft)
   var timestampRight = startOfDayRight.getTime() -
-    startOfDayRight.getTimezoneOffset() * MILLISECONDS_IN_MINUTE
+    getTimezoneOffsetInMilliseconds(startOfDayRight)
 
   // Round the number of days to the nearest integer
   // because the number of milliseconds in a day is not constant

src/differenceInCalendarISOWeeks/index.js

@@ -1,6 +1,6 @@
+import getTimezoneOffsetInMilliseconds from '../_lib/getTimezoneOffsetInMilliseconds/index.js'
 import startOfISOWeek from '../startOfISOWeek/index.js'
 
-var MILLISECONDS_IN_MINUTE = 60000
 var MILLISECONDS_IN_WEEK = 604800000
 
 /**
@@ -38,9 +38,9 @@ export default function differenceInCalendarISOWeeks (dirtyDateLeft, dirtyDateRi
   var startOfISOWeekRight = startOfISOWeek(dirtyDateRight, dirtyOptions)
 
   var timestampLeft = startOfISOWeekLeft.getTime() -
-    startOfISOWeekLeft.getTimezoneOffset() * MILLISECONDS_IN_MINUTE
+    getTimezoneOffsetInMilliseconds(startOfISOWeekLeft)
   var timestampRight = startOfISOWeekRight.getTime() -
-    startOfISOWeekRight.getTimezoneOffset() * MILLISECONDS_IN_MINUTE
+    getTimezoneOffsetInMilliseconds(startOfISOWeekRight)
 
   // Round the number of days to the nearest integer
   // because the number of milliseconds in a week is not constant

src/differenceInCalendarWeeks/index.js

@@ -1,6 +1,6 @@
+import getTimezoneOffsetInMilliseconds from '../_lib/getTimezoneOffsetInMilliseconds/index.js'
 import startOfWeek from '../startOfWeek/index.js'
 
-var MILLISECONDS_IN_MINUTE = 60000
 var MILLISECONDS_IN_WEEK = 604800000
 
 /**
@@ -49,9 +49,9 @@ export default function differenceInCalendarWeeks (dirtyDateLeft, dirtyDateRight
   var startOfWeekRight = startOfWeek(dirtyDateRight, dirtyOptions)
 
   var timestampLeft = startOfWeekLeft.getTime() -
-    startOfWeekLeft.getTimezoneOffset() * MILLISECONDS_IN_MINUTE
+    getTimezoneOffsetInMilliseconds(startOfWeekLeft)
   var timestampRight = startOfWeekRight.getTime() -
-    startOfWeekRight.getTimezoneOffset() * MILLISECONDS_IN_MINUTE
+    getTimezoneOffsetInMilliseconds(startOfWeekRight)
 
   // Round the number of days to the nearest integer
   // because the number of milliseconds in a week is not constant

src/format/index.js

@@ -1,10 +1,11 @@
 import toInteger from '../_lib/toInteger/index.js'
+import getTimezoneOffsetInMilliseconds from '../_lib/getTimezoneOffsetInMilliseconds/index.js'
 import toDate from '../toDate/index.js'
 import isValid from '../isValid/index.js'
 import defaultLocale from '../locale/en-US/index.js'
 import formatters from './_lib/formatters/index.js'
 import longFormatters from './_lib/longFormatters/index.js'
-import addUTCMinutes from '../_lib/addUTCMinutes/index.js'
+import subMilliseconds from '../subMilliseconds/index.js'
 
 // This RegExp consists of three parts separated by `|`:
 // - [yYQqMLwIdDecihHKkms]o matches any available ordinal number token
@@ -359,8 +360,8 @@ export default function format (dirtyDate, dirtyFormatStr, dirtyOptions) {
   // Convert the date in system timezone to the same date in UTC+00:00 timezone.
   // This ensures that when UTC functions will be implemented, locales will be compatible with them.
   // See an issue about UTC functions: https://github.com/date-fns/date-fns/issues/376
-  var timezoneOffset = originalDate.getTimezoneOffset()
-  var utcDate = addUTCMinutes(originalDate, -timezoneOffset, options)
+  var timezoneOffset = getTimezoneOffsetInMilliseconds(originalDate)
+  var utcDate = subMilliseconds(originalDate, timezoneOffset, options)
 
   var formatterOptions = {
     firstWeekContainsDate: firstWeekContainsDate,

src/formatDistance/index.js

@@ -1,3 +1,4 @@
+import getTimezoneOffsetInMilliseconds from '../_lib/getTimezoneOffsetInMilliseconds/index.js'
 import compareAsc from '../compareAsc/index.js'
 import toDate from '../toDate/index.js'
 import differenceInSeconds from '../differenceInSeconds/index.js'
@@ -130,8 +131,8 @@ export default function formatDistance (dirtyDate, dirtyBaseDate, dirtyOptions)
   }
 
   var seconds = differenceInSeconds(dateRight, dateLeft, options)
-  var offset = dateRight.getTimezoneOffset() - dateLeft.getTimezoneOffset()
-  var minutes = Math.round(seconds / 60) - offset
+  var offsetInSeconds = (getTimezoneOffsetInMilliseconds(dateRight) - getTimezoneOffsetInMilliseconds(dateLeft)) / 1000
+  var minutes = Math.round((seconds - offsetInSeconds) / 60)
   var months
 
   // 0 up to 2 mins

src/formatDistanceStrict/index.js

@@ -1,3 +1,4 @@
+import getTimezoneOffsetInMilliseconds from '../_lib/getTimezoneOffsetInMilliseconds/index.js'
 import compareAsc from '../compareAsc/index.js'
 import toDate from '../toDate/index.js'
 import differenceInSeconds from '../differenceInSeconds/index.js'
@@ -145,8 +146,8 @@ export default function formatDistanceStrict (dirtyDate, dirtyBaseDate, dirtyOpt
   }
 
   var seconds = differenceInSeconds(dateRight, dateLeft, dirtyOptions)
-  var offset = dateRight.getTimezoneOffset() - dateLeft.getTimezoneOffset()
-  var minutes = roundingMethodFn(seconds / 60) - offset
+  var offsetInSeconds = (getTimezoneOffsetInMilliseconds(dateRight) - getTimezoneOffsetInMilliseconds(dateLeft)) / 1000
+  var minutes = roundingMethodFn((seconds - offsetInSeconds) / 60)
 
   var unit
   if (options.unit == null) {

src/formatRelative/index.js

@@ -1,8 +1,9 @@
+import getTimezoneOffsetInMilliseconds from '../_lib/getTimezoneOffsetInMilliseconds/index.js'
 import toDate from '../toDate/index.js'
 import format from '../format/index.js'
 import differenceInCalendarDays from '../differenceInCalendarDays/index.js'
 import defaultLocale from '../locale/en-US/index.js'
-import subMinutes from '../subMinutes/index.js'
+import subMilliseconds from '../subMilliseconds/index.js'
 
 /**
  * @name formatRelative
@@ -78,8 +79,8 @@ export default function formatRelative (dirtyDate, dirtyBaseDate, dirtyOptions)
     token = 'other'
   }
 
-  var utcDate = subMinutes(date, date.getTimezoneOffset(), options)
-  var utcBaseDate = subMinutes(baseDate, date.getTimezoneOffset(), options)
+  var utcDate = subMilliseconds(date, getTimezoneOffsetInMilliseconds(date), options)
+  var utcBaseDate = subMilliseconds(baseDate, getTimezoneOffsetInMilliseconds(baseDate), options)
   var formatStr = locale.formatRelative(token, utcDate, utcBaseDate, options)
   return format(date, formatStr, options)
 }

src/parse/index.js

@@ -1,6 +1,7 @@
 import toInteger from '../_lib/toInteger/index.js'
+import getTimezoneOffsetInMilliseconds from '../_lib/getTimezoneOffsetInMilliseconds/index.js'
 import toDate from '../toDate/index.js'
-import subMinutes from '../subMinutes/index.js'
+import subMilliseconds from '../subMilliseconds/index.js'
 import defaultLocale from '../locale/en-US/index.js'
 import parsers from './_lib/parsers/index.js'
 
@@ -416,7 +417,7 @@ export default function parse (dirtyDateString, dirtyFormatString, dirtyBaseDate
   // Convert the date in system timezone to the same date in UTC+00:00 timezone.
   // This ensures that when UTC functions will be implemented, locales will be compatible with them.
   // See an issue about UTC functions: https://github.com/date-fns/date-fns/issues/37
-  var utcDate = subMinutes(date, date.getTimezoneOffset())
+  var utcDate = subMilliseconds(date, getTimezoneOffsetInMilliseconds(date))
 
   for (i = 0; i < uniquePrioritySetters.length; i++) {
     var setter = uniquePrioritySetters[i]

src/toDate/index.js

@@ -1,4 +1,5 @@
 import toInteger from '../_lib/toInteger/index.js'
+import getTimezoneOffsetInMilliseconds from '../_lib/getTimezoneOffsetInMilliseconds/index.js'
 
 var MILLISECONDS_IN_HOUR = 3600000
 var MILLISECONDS_IN_MINUTE = 60000
@@ -128,11 +129,11 @@ export default function toDate (argument, dirtyOptions) {
       offset = parseTimezone(dateStrings.timezone)
     } else {
       // get offset accurate to hour in timezones that change offset
-      offset = new Date(timestamp + time).getTimezoneOffset()
-      offset = new Date(timestamp + time + offset * MILLISECONDS_IN_MINUTE).getTimezoneOffset()
+      offset = getTimezoneOffsetInMilliseconds(new Date(timestamp + time))
+      offset = getTimezoneOffsetInMilliseconds(new Date(timestamp + time + offset))
     }
 
-    return new Date(timestamp + time + offset * MILLISECONDS_IN_MINUTE)
+    return new Date(timestamp + time + offset)
   } else {
     return new Date(NaN)
   }
@@ -314,14 +315,14 @@ function parseTimezone (timezoneString) {
   // ±hh
   token = patterns.timezoneHH.exec(timezoneString)
   if (token) {
-    absoluteOffset = parseInt(token[2], 10) * 60
+    absoluteOffset = parseInt(token[2], 10) * MILLISECONDS_IN_HOUR
     return (token[1] === '+') ? -absoluteOffset : absoluteOffset
   }
 
   // ±hh:mm or ±hhmm
   token = patterns.timezoneHHMM.exec(timezoneString)
   if (token) {
-    absoluteOffset = parseInt(token[2], 10) * 60 + parseInt(token[3], 10)
+    absoluteOffset = parseInt(token[2], 10) * MILLISECONDS_IN_HOUR + parseInt(token[3], 10) * MILLISECONDS_IN_MINUTE
     return (token[1] === '+') ? -absoluteOffset : absoluteOffset
   }