fix: fix DST bug in utc plugin (#1053)

Author: iamkun

src/index.js

@@ -1,6 +1,6 @@
 import * as C from './constant'
-import U from './utils'
 import en from './locale/en'
+import U from './utils'
 
 let L = 'en' // global locale
 const Ls = {} // global loaded locale
@@ -43,6 +43,7 @@ const wrapper = (date, instance) =>
   dayjs(date, {
     locale: instance.$L,
     utc: instance.$u,
+    x: instance.$x,
     $offset: instance.$offset // todo: refactor; do not use this.$offset in you code
   })
 
@@ -81,6 +82,7 @@ class Dayjs {
 
   parse(cfg) {
     this.$d = parseDate(cfg)
+    this.$x = cfg.x || {}
     this.init()
   }
 

src/plugin/utc/index.js

@@ -1,7 +1,6 @@
 import { MILLISECONDS_A_MINUTE, MIN } from '../../constant'
 
 export default (option, Dayjs, dayjs) => {
-  const localOffset = (new Date()).getTimezoneOffset()
   const proto = Dayjs.prototype
   dayjs.utc = function (date) {
     const cfg = { date, utc: true, args: arguments } // eslint-disable-line prefer-rest-params
@@ -64,8 +63,11 @@ export default (option, Dayjs, dayjs) => {
       return ins
     }
     if (input !== 0) {
-      ins = this.local().add(offset + localOffset, MIN)
+      const localTimezoneOffset = this.$u
+        ? this.toDate().getTimezoneOffset() : -1 * this.utcOffset()
+      ins = this.local().add(offset + localTimezoneOffset, MIN)
       ins.$offset = offset
+      ins.$x.$localOffset = localTimezoneOffset
     } else {
       ins = this.utc()
     }
@@ -81,7 +83,7 @@ export default (option, Dayjs, dayjs) => {
 
   proto.valueOf = function () {
     const addedOffset = !this.$utils().u(this.$offset)
-      ? this.$offset + localOffset : 0
+      ? this.$offset + (this.$x.$localOffset || (new Date()).getTimezoneOffset()) : 0
     return this.$d.valueOf() - (addedOffset * MILLISECONDS_A_MINUTE)
   }
 

test/timezone.test.js

@@ -1,5 +1,5 @@
-import moment from 'moment'
 import MockDate from 'mockdate'
+import moment from 'moment'
 import dayjs from '../src'
 import utc from '../src/plugin/utc'
 
@@ -54,3 +54,11 @@ it('UTC add day in DST', () => {
     .toBe(momentTest.clone().add(2, 'day').format())
 })
 
+it('UTC and utcOffset', () => {
+  const test1 = 1331449199000 // 2012/3/11 14:59:59
+  expect(moment(test1).utcOffset(-300).format())
+    .toBe(dayjs(test1).utcOffset(-300).format())
+  const test2 = '2000-01-01T06:31:00Z'
+  expect(moment.utc(test2).utcOffset(-60).format())
+    .toBe(dayjs.utc(test2).utcOffset(-60).format())
+})