Fix timezone offset range and month boundary in isValid

- Remove local timezone dependency in getLastDayOfMonth by using Date.UTC
- Expand timezone offset (Z token) valid range from -840~720 to -913~956
  to support historical timezone offsets (e.g., Metlakatla, Manila)
- Add test cases for min (America/Metlakatla) and max (Asia/Manila) offsets

Author: knowledgecode

src/isValid.ts

@@ -4,7 +4,7 @@ import type { ParserOptions } from './parser.ts';
 import type { PreparseResult } from './preparse.ts';
 
 const getLastDayOfMonth = (year: number, month: number) => {
-  return new Date(year, month - (year < 100 ? 1900 * 12 : 0), 0).getDate();
+  return new Date(Date.UTC(year, month - (year < 100 ? 1900 * 12 : 0), 0)).getUTCDate();
 };
 
 /**
@@ -32,7 +32,7 @@ export function validatePreparseResult(pr: PreparseResult, options?: ParserOptio
     && range(pr.m, 0, 59)
     && range(pr.s, 0, 59)
     && range(pr.S, 0, 999)
-    && range(pr.Z, -840, 720);
+    && range(pr.Z, -913, 956);
 }
 
 /**

tests/isValid.spec.ts

@@ -1,5 +1,5 @@
 import { describe, expect, test, beforeAll } from 'vitest';
-import { isValid, compile } from '@/index.ts';
+import { isValid, compile, format } from '@/index.ts';
 import { parser } from '@/plugins/day-of-week.ts';
 
 beforeAll(() => (process.env.TZ = 'UTC'));
@@ -137,4 +137,16 @@ describe('options', () => {
     expect(isValid('0544-01-01 12:00 AM', 'YYYY-MM-DD hh:mm A', { calendar: 'buddhist' })).toBe(true);
     expect(isValid('0543-01-01 12:00 AM', 'YYYY-MM-DD hh:mm A', { calendar: 'buddhist' })).toBe(false);
   });
+
+  test('timeZone: min', () => {
+    process.env.TZ = 'America/Metlakatla';
+    const dateString = format(new Date(-3225223728000), 'YYYY-MM-DD[T]HH:mm:ss ZZ');
+    expect(isValid(dateString, 'YYYY-MM-DD[T]HH:mm:ss ZZ')).toBe(true);
+  });
+
+  test('timeZone: max', () => {
+    process.env.TZ = 'Asia/Manila';
+    const dateString = format(new Date(-3944621033000), 'YYYY-MM-DD[T]HH:mm:ss ZZ');
+    expect(isValid(dateString, 'YYYY-MM-DD[T]HH:mm:ss ZZ')).toBe(true);
+  });
 });