Remove dependency on Moment library in exchange for date-fns-tz

package.json

@@ -54,7 +54,7 @@
     "colors": true
   },
   "dependencies": {
-    "moment-timezone": "^0.5.39"
+    "date-fns-tz": "^1.3.7"
   },
   "devDependencies": {
     "c8": "^7.12.0",
@@ -68,7 +68,8 @@
     "npm-run-all": "^4.1.5",
     "rimraf": "^3.0.2",
     "rollup": "^3.3.0",
-    "typescript": "^4.9.3"
+    "typescript": "^4.9.3",
+    "date-fns":"^2.29.3"
   },
   "engines": {
     "node": ">=12.0.0"

src/CalDate.js

@@ -1,6 +1,6 @@
-
-import moment from 'moment-timezone'
 import { toYear, toNumber, isDate, pad0 } from './utils.js'
+import utcToZonedTime from 'date-fns-tz/utcToZonedTime'
+import zonedTimeToUtc from 'date-fns-tz/zonedTimeToUtc'
 
 const PROPS = ['year', 'month', 'day', 'hour', 'minute', 'second']
 
@@ -180,9 +180,17 @@ export class CalDate {
    * @param {String} timezone - e.g. 'America/New_York'
    * @return {Date}
    */
-  toTimezone (timezone) {
-    if (timezone) {
-      return new Date(moment.tz(this.toString(), timezone).format())
+  toTimezone (timeZone) {
+    if (timeZone) {
+      const returnVar = zonedTimeToUtc(this.toString(), timeZone)
+      // hack alert - tehran has the only timezone which starts daylight saving at midnight (although stopped DST in 2022)
+      // once the bug in zoneTimeToUtc is fixed, delete this hack https://github.com/marnusw/date-fns-tz/issues/222
+      if (timeZone === 'Asia/Tehran') {
+        const i = new Intl.DateTimeFormat('en', { timeZone, hourCycle: 'h23', hour: 'numeric' })
+        const f = parseInt(i.format(returnVar), 10)
+        if (f !== this.hour) returnVar.setHours(returnVar.getHours() + 1)
+      }
+      return returnVar
     } else {
       return this.toDate()
     }
@@ -196,13 +204,13 @@ export class CalDate {
    */
   fromTimezone (dateUTC, timezone) {
     if (timezone) {
-      const m = moment.tz(dateUTC, timezone)
-      this.year = m.year()
-      this.month = m.month() + 1
-      this.day = m.date()
-      this.hour = m.hours()
-      this.minute = m.minutes()
-      this.second = m.seconds()
+      const m = utcToZonedTime(dateUTC, timezone)
+      this.year = m.getFullYear()
+      this.month = m.getMonth() + 1
+      this.day = m.getDate()
+      this.hour = m.getHours()
+      this.minute = m.getMinutes()
+      this.second = m.getSeconds()
     } else {
       this.set(dateUTC)
     }

test/CalDate.mocha.js

@@ -96,6 +96,12 @@ describe('#CalDate', function () {
     assert.strictEqual(res, '2000-01-01T05:00:00.000Z')
   })
 
+  it('can move date by timezone with daylight saving offset', function () {
+    const caldate = new CalDate(new Date('2000-07-01 00:00:00'))
+    const res = caldate.toTimezone('America/New_York').toISOString()
+    assert.strictEqual(res, '2000-07-01T04:00:00.000Z')
+  })
+
   it('can return date in current timezone', function () {
     const caldate = new CalDate({ year: 2000, month: 1, day: 1 })
     const exp = new Date('2000-01-01 00:00:00')
@@ -199,3 +205,64 @@ describe('#CalDate', function () {
     assert.strictEqual(res, exp)
   })
 })
+
+describe('handles daylight saving jumps', function () {
+  it('finds first time after clock jumps back: -ve UTC offset', function () {
+    const caldate = new CalDate(new Date('2023-11-05 02:00:00'))
+    const res = caldate.toTimezone('America/New_York').toISOString()
+    // UTC 05:59 is NY 01:59 GMT -4
+    // UTC 06:00 is NY 01:00 GMT -5
+    // therefore the first time NY local 02:00 is struck is UTC 07:00
+    assert.strictEqual(res, '2023-11-05T07:00:00.000Z')
+  })
+
+  it('finds first time after clock jumps back: +ve UTC offset', function () {
+    const caldate = new CalDate(new Date('2023-04-02 03:00:00'))
+    const res = caldate.toTimezone('Australia/Sydney').toISOString()
+    // UTC 15:59 is SYD 02:59 GMT +11
+    // UTC 16:00 is SYD 02:00 GMT +10
+    // therefore the first time SYD local 03:00 is struck is UTC 17:00
+    assert.strictEqual(res, '2023-04-01T17:00:00.000Z')
+  })
+
+  it('handles times that repeat when clock jump back: -ve UTC offset', function () {
+    // at 02:00 local clock jumps back 1 hour so 01:00 occurs twice
+    const caldate = new CalDate(new Date('2023-11-05 01:00:00'))
+    const res = caldate.toTimezone('America/New_York').toISOString()
+    // UTC 05:00 is NY 01:00 GMT -4
+    // UTC 06:00 is NY 01:00 GMT -5
+    // this implementation picks the later occurrence of 01:00 @ UTC 06:00
+    assert.strictEqual(res, '2023-11-05T06:00:00.000Z')
+  })
+
+  it('handles times that repeat when clock jump back: +ve UTC offset', function () {
+    // at 03:00 local clock jumps back 1 hour so 02:00 occurs twice
+    const caldate = new CalDate(new Date('2023-04-02 02:00:00'))
+    const res = caldate.toTimezone('Australia/Sydney').toISOString()
+    // UTC 15:00 is SYD 02:00 GMT +11
+    // UTC 16:00 is SYD 02:00 GMT +10
+    // this implementation picks the later occurrence of 02:00 @ UTC 16:00
+    assert.strictEqual(res, '2023-04-01T16:00:00.000Z')
+  })
+
+  // utc: 2023-09-30T16:00:00.000Z SYD: 03:00 GMT+11
+  it('handles times that dont exist with clock jump forward: -ve UTC offset', function () {
+    // at 02:00 local clock will immediately jump forward to 03:00
+    const caldate = new CalDate(new Date('2023-03-12 02:00:00'))
+    const res = caldate.toTimezone('America/New_York').toISOString()
+    // UTC 06:59 is NY 01:59 GMT -5
+    // UTC 07:00 is NY 03:00 GMT -4
+    // !! this is an error - should either throw error or return UTC 07:00
+    assert.strictEqual(res, '2023-03-12T06:00:00.000Z')
+  })
+
+  it('handles times that dont exist with clock jump forward: +ve UTC offset', function () {
+    // at 02:00 local clock will immediately jump forward to 03:00
+    const caldate = new CalDate(new Date('2023-10-01 02:00:00'))
+    const res = caldate.toTimezone('Australia/Sydney').toISOString()
+    // UTC 15:59 is SYD 01:59 GMT +10
+    // UTC 16:00 is SYD 03:00 GMT +11
+    // !! this is an error - should either throw error or return UTC 16:00
+    assert.strictEqual(res, '2023-09-30T15:00:00.000Z')
+  })
+})