fix: The time zone offset is incorrectly calculated when the DST exits at 00:00.

package.json

@@ -5,9 +5,13 @@
   "main": "dayjs.min.js",
   "types": "index.d.ts",
   "scripts": {
-    "test": "TZ=Pacific/Auckland npm run test-tz && TZ=Europe/London npm run test-tz && TZ=America/Whitehorse npm run test-tz && npm run test-tz && jest",
+    "test": "npm run test-tz && npm run test-tz1 && npm run test-tz2 && npm run test-tz3 && npm run test-tz4 && jest",
     "test-tz": "date && jest test/timezone.test --coverage=false",
-    "lint": "./node_modules/.bin/eslint src/* test/* build/*",
+    "test-tz1": "cross-env TZ=Pacific/Auckland npm run test-tz",
+    "test-tz2": "cross-env TZ=Europe/London npm run test-tz",
+    "test-tz3": "cross-env TZ=America/Whitehorse npm run test-tz",
+    "test-tz4": "cross-env TZ=America/Asuncion npm run test-tz",
+    "lint": "eslint src/* test/* build/*",
     "prettier": "prettier --write \"docs/**/*.md\"",
     "babel": "cross-env BABEL_ENV=build babel src --out-dir esm --copy-files && node build/esm",
     "build": "cross-env BABEL_ENV=build node build && npm run size",

src/plugin/timezone/index.js

@@ -96,8 +96,7 @@ export default (o, c, d) => {
     const oldOffset = this.utcOffset()
     const date = this.toDate()
     const target = date.toLocaleString('en-US', { timeZone: timezone })
-    const diff = Math.round((date - new Date(target)) / 1000 / 60)
-    const offset = (-Math.round(date.getTimezoneOffset() / 15) * 15) - diff
+    const offset = tzOffset(date.getTime(), timezone)
     const isUTC = !Number(offset)
     let ins
     if (isUTC) { // if utcOffset is 0, turn it to UTC mode

test/timezone.test.js

@@ -80,3 +80,15 @@ it('UTC diff in DST', () => {
   expect(day1.diff(day2, 'd'))
     .toBe(-3)
 })
+
+describe('Test America/Asuncion', () => {
+  it('Entering daylight saving time', () => {
+    const testDate = dayjs('2024-03-24T02:20:57.000+00:00').tz('America/Asuncion').format('YYYY-MM-DD HH:mm:ssZ')
+    expect(testDate).toBe('2024-03-23 23:20:57-03:00')
+  })
+
+  it('Exit daylight saving time', () => {
+    const testDate = dayjs('2024-03-24T03:20:57.000+00:00').tz('America/Asuncion').format('YYYY-MM-DD HH:mm:ssZ')
+    expect(testDate).toBe('2024-03-23 23:20:57-04:00')
+  })
+})