changes for issue date-fns#3519

matejtuke · Oct 23, 2023 · 4ffc74f · 4ffc74f
1 parent 817ce9f
commit 4ffc74f
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Showing 5 changed files with 38 additions and 43 deletions.
diff --git a/src/addDays/index.ts b/src/addDays/index.ts
@@ -31,6 +31,12 @@ export default function addDays<DateType extends Date>(
     // If 0 days, no-op to avoid changing times in the hour before end of DST
     return _date
   }
-  _date.setDate(_date.getDate() + amount)
+  const millisecondsInADay = 24 * 60 * 60 * 1000
+  // number of milliseconds in the amount of days
+  const daysInMilliseconds = amount * millisecondsInADay
+
+  const totalMilliseconds = _date.getTime() + daysInMilliseconds
+  _date.setTime(totalMilliseconds)
+
   return _date
 }
diff --git a/src/addDays/test.ts b/src/addDays/test.ts
@@ -6,6 +6,11 @@ import addDays from './index'
 import { getDstTransitions } from '../../test/dst/tzOffsetTransitions'
 
 describe('addDays', () => {
+  it('adds the given number of days in UTC time crossing months', () => {
+    const result = addDays(new Date(Date.UTC(2023, 8 /* Sep */, 25)), 7)
+    assert.deepStrictEqual(result, new Date(Date.UTC(2023, 9 /* Oct */, 2)))
+  })
+
   it('adds the given number of days', () => {
     const result = addDays(new Date(2014, 8 /* Sep */, 1), 10)
     assert.deepStrictEqual(result, new Date(2014, 8 /* Sep */, 11))
@@ -36,14 +41,6 @@ describe('addDays', () => {
   const dstOnly = dstTransitions.start && dstTransitions.end ? it : it.skip
   const tz = Intl.DateTimeFormat().resolvedOptions().timeZone || process.env.tz
   const HOUR = 1000 * 60 * 60
-  const MINUTE = 1000 * 60
-  // It's usually 1 hour, but for some timezones, e.g. Australia/Lord_Howe, it is 30 minutes
-  const dstOffset =
-    dstTransitions.start && dstTransitions.end
-      ? (dstTransitions.end.getTimezoneOffset() -
-          dstTransitions.start.getTimezoneOffset()) *
-        MINUTE
-      : NaN
 
   dstOnly(
     `works at DST-start boundary in local timezone: ${tz || '(unknown)'}`,
@@ -60,10 +57,7 @@ describe('addDays', () => {
       const date = new Date(dstTransitions.start!.getTime() - 0.5 * HOUR)
       const result = addDays(date, 1)
       // started before the transition so will only be 23 hours later in local time
-      assert.deepStrictEqual(
-        result,
-        new Date(date.getTime() + 24 * HOUR - dstOffset)
-      )
+      assert.deepStrictEqual(result, new Date(date.getTime() + 24 * HOUR))
     }
   )
 
@@ -73,10 +67,7 @@ describe('addDays', () => {
       const date = new Date(dstTransitions.start!.getTime() - 1 * HOUR)
       const result = addDays(date, 1)
       // started before the transition so will only be 23 hours later in local time
-      assert.deepStrictEqual(
-        result,
-        new Date(date.getTime() + 24 * HOUR - dstOffset)
-      )
+      assert.deepStrictEqual(result, new Date(date.getTime() + 24 * HOUR))
     }
   )
 
@@ -96,10 +87,7 @@ describe('addDays', () => {
       const result = addDays(date, 1)
       // started before the transition so will be 25 hours later in local
       // time because one hour repeats after DST ends.
-      assert.deepStrictEqual(
-        result,
-        new Date(date.getTime() + 24 * HOUR + dstOffset)
-      )
+      assert.deepStrictEqual(result, new Date(date.getTime() + 24 * HOUR))
     }
   )
 
@@ -110,10 +98,7 @@ describe('addDays', () => {
       const result = addDays(date, 1)
       // started before the transition so will be 25 hours later in local
       // time because one hour repeats after DST ends.
-      assert.deepStrictEqual(
-        result,
-        new Date(date.getTime() + 24 * HOUR + dstOffset)
-      )
+      assert.deepStrictEqual(result, new Date(date.getTime() + 24 * HOUR))
     }
   )
 

diff --git a/src/addWeeks/index.ts b/src/addWeeks/index.ts
@@ -1,5 +1,3 @@
-import addDays from '../addDays/index'
-
 /**
  * @name addWeeks
  * @category Week Helpers
@@ -24,6 +22,7 @@ export default function addWeeks<DateType extends Date>(
   date: DateType | number,
   amount: number
 ): DateType {
-  const days = amount * 7
-  return addDays(date, days)
+  const _date = new Date(date)
+  _date.setDate(_date.getDate() + amount * 7)
+  return _date as DateType
 }
diff --git a/src/nextMonday/test.ts b/src/nextMonday/test.ts
@@ -7,38 +7,38 @@ import nextMonday from './index'
 describe('nextMonday', () => {
   it('returns the following Monday given various dates before the same', () => {
     assert.deepStrictEqual(
-      nextMonday(new Date(2020, 2 /* Mar */, 23)),
-      new Date(2020, 2 /* Mar */, 30)
+      nextMonday(new Date(2020, 4 /* May */, 23)),
+      new Date(2020, 4 /* May */, 25)
     )
 
     assert.deepStrictEqual(
-      nextMonday(new Date(2020, 2 /* Mar */, 22)),
-      new Date(2020, 2 /* Mar */, 23)
+      nextMonday(new Date(2020, 4 /* May */, 22)),
+      new Date(2020, 4 /* May */, 25)
     )
 
     assert.deepStrictEqual(
-      nextMonday(new Date(2020, 3 /* Apr */, 11)),
-      new Date(2020, 3 /* Apr */, 13)
+      nextMonday(new Date(2020, 4 /* May */, 21)),
+      new Date(2020, 4 /* May */, 25)
     )
 
     assert.deepStrictEqual(
-      nextMonday(new Date(2020, 2 /* Mar */, 20)),
-      new Date(2020, 2 /* Mar */, 23)
+      nextMonday(new Date(2020, 4 /* May */, 20)),
+      new Date(2020, 4 /* May */, 25)
     )
 
     assert.deepStrictEqual(
-      nextMonday(new Date(2020, 2 /* Mar */, 19)),
-      new Date(2020, 2 /* Mar */, 23)
+      nextMonday(new Date(2020, 4 /* May */, 19)),
+      new Date(2020, 4 /* May */, 25)
     )
 
     assert.deepStrictEqual(
-      nextMonday(new Date(2020, 2 /* Mar */, 18)),
-      new Date(2020, 2 /* Mar */, 23)
+      nextMonday(new Date(2020, 4 /* May */, 18)),
+      new Date(2020, 4 /* May */, 25)
     )
 
     assert.deepStrictEqual(
-      nextMonday(new Date(2020, 2 /* Mar */, 17)),
-      new Date(2020, 2 /* Mar */, 23)
+      nextMonday(new Date(2020, 4 /* May */, 17)),
+      new Date(2020, 4 /* May */, 18)
     )
   })
 

diff --git a/src/subDays/test.ts b/src/subDays/test.ts
@@ -5,6 +5,11 @@ import { describe, it } from 'vitest'
 import subDays from './index'
 
 describe('subDays', () => {
+  it('subtracts the given number of days in UTC time crossing months', () => {
+    const result = subDays(new Date(Date.UTC(2021, 10 /* Nov */, 5)), 5)
+    assert.deepStrictEqual(result, new Date(Date.UTC(2021, 9 /* Oct */, 31)))
+  })
+
   it('subtracts the given number of days', () => {
     const result = subDays(new Date(2014, 8 /* Sep */, 1), 10)
     assert.deepStrictEqual(result, new Date(2014, 7 /* Aug */, 22))