fix: Fix set utcOffset in utc mode

Author: iamkun

src/index.js

@@ -39,7 +39,12 @@ const dayjs = (date, c, pl) => {
 }
 
 const wrapper = (date, instance) =>
-  dayjs(date, { locale: instance.$L, utc: instance.$u, $offset: instance.$offset })
+  dayjs(date, {
+    locale: instance.$L,
+    utc: instance.$u,
+    $offset: instance.$offset, // todo: refactor; do not use this.$offset this.$lo in you code
+    $lo: instance.$lo // save local utcoffset; todo: refactor
+  })
 
 const Utils = U // for plugin use
 Utils.l = parseLocale

src/plugin/utc/index.js

@@ -24,6 +24,9 @@ export default (option, Dayjs, dayjs) => {
     if (!this.$utils().u(cfg.$offset)) {
       this.$offset = cfg.$offset
     }
+    if (!this.$utils().u(cfg.$lo)) {
+      this.$lo = cfg.$lo
+    }
     oldParse.call(this, cfg)
   }
 
@@ -59,6 +62,7 @@ export default (option, Dayjs, dayjs) => {
     const offset = Math.abs(input) <= 16 ? input * 60 : input
     const newD = this.add(offset + (this.$u ? 0 : localOffset), MIN)
     newD.$offset = offset
+    newD.$lo = this.$u ? 0 : localOffset
     newD.$u = input === 0 // UTC mode
     return newD
   }
@@ -72,7 +76,7 @@ export default (option, Dayjs, dayjs) => {
 
   proto.valueOf = function () {
     const addedOffset = !this.$utils().u(this.$offset)
-      ? this.$offset + localOffset : 0
+      ? this.$offset + this.$lo : 0
     return this.$d.valueOf() - (addedOffset * MILLISECONDS_A_MINUTE)
   }
 

test/plugin/utc-utcOffset.test.js

@@ -75,3 +75,16 @@ test('change hours when changing the utc offset in UTC mode', () => {
   expect(d.utcOffset(30).format('HH:mm')).toBe('07:01')
   expect(d.utcOffset(-1380).format('HH:mm')).toBe('07:31')
 })
+
+test('utc costrustor', () => {
+  const d = new Date(2019, 8, 11, 0, 0, 0).getTime()
+  expect(moment(d).utc().utcOffset(480).valueOf())
+    .toBe(dayjs(d).utc().utcOffset(480).valueOf())
+
+  expect(moment(d).utc().local()
+    .utcOffset(480)
+    .valueOf())
+    .toBe(dayjs(d).utc().local()
+      .utcOffset(480)
+      .valueOf())
+})