fix: update Duration plugin add/subtract take into account days in month (#2337)

Author: alexander-ulaev

src/plugin/duration/index.js

@@ -257,6 +257,15 @@ class Duration {
   asYears() { return this.as('years') }
 }
 
+const manipulateDuration = (date, duration, k) =>
+  date.add(duration.years() * k, 'y')
+    .add(duration.months() * k, 'M')
+    .add(duration.days() * k, 'd')
+    .add(duration.hours() * k, 'h')
+    .add(duration.minutes() * k, 'm')
+    .add(duration.seconds() * k, 's')
+    .add(duration.milliseconds() * k, 'ms')
+
 export default (option, Dayjs, dayjs) => {
   $d = dayjs
   $u = dayjs().$utils()
@@ -268,12 +277,20 @@ export default (option, Dayjs, dayjs) => {
 
   const oldAdd = Dayjs.prototype.add
   const oldSubtract = Dayjs.prototype.subtract
+
   Dayjs.prototype.add = function (value, unit) {
-    if (isDuration(value)) value = value.asMilliseconds()
+    if (isDuration(value)) {
+      return manipulateDuration(this, value, 1)
+    }
+
     return oldAdd.bind(this)(value, unit)
   }
+
   Dayjs.prototype.subtract = function (value, unit) {
-    if (isDuration(value)) value = value.asMilliseconds()
+    if (isDuration(value)) {
+      return manipulateDuration(this, value, -1)
+    }
+
     return oldSubtract.bind(this)(value, unit)
   }
 }

test/plugin/duration.test.js

@@ -182,6 +182,10 @@ test('Add duration', () => {
   const a = dayjs('2020-10-01')
   const days = dayjs.duration(2, 'days')
   expect(a.add(days).format('YYYY-MM-DD')).toBe('2020-10-03')
+
+  const b = dayjs('2023-02-01 00:00:00')
+  const p = dayjs.duration('P1Y1M1DT1H1M1S')
+  expect(b.add(p).format('YYYY-MM-DD HH:mm:ss')).toBe('2024-03-02 01:01:01')
 })
 
 describe('Subtract', () => {
@@ -194,6 +198,10 @@ test('Subtract duration', () => {
   const a = dayjs('2020-10-20')
   const days = dayjs.duration(2, 'days')
   expect(a.subtract(days).format('YYYY-MM-DD')).toBe('2020-10-18')
+
+  const b = dayjs('2023-03-02 02:02:02')
+  const p = dayjs.duration('P1Y1M1DT1H1M1S')
+  expect(b.subtract(p).format('YYYY-MM-DD HH:mm:ss')).toBe('2022-02-01 01:01:01')
 })
 
 describe('Seconds', () => {