fix(@axhxrx/date): fix bug caused by adding tests 😂

Author: Bottie McBotface

dateToIS08601WithTimeZoneOffset.test.ts

@@ -37,3 +37,24 @@ Deno.test('format ignoring milliseconds', () =>
   const result = dateToIS08601WithTimeZoneOffset(date, testTimezoneOffset);
   assertEquals(result, '2023-10-01T21:00:00+09:00');
 });
+
+Deno.test('format a valid date with an overridden time zone offset', () =>
+{
+  const date = new Date('2023-10-01T12:00:00Z');
+  const result = dateToIS08601WithTimeZoneOffset(date, 540);
+  assertEquals(result, '2023-10-01T03:00:00-09:00');
+});
+
+Deno.test('format a valid date with an overridden time zone offset into the previous day', () =>
+{
+  const date = new Date('2023-10-01T01:00:00Z');
+  const result = dateToIS08601WithTimeZoneOffset(date, 540);
+  assertEquals(result, '2023-09-30T16:00:00-09:00');
+});
+
+Deno.test('format a valid date with an overridden time zone offset into the next day', () =>
+{
+  const date = new Date('2023-10-01T23:00:00Z');
+  const result = dateToIS08601WithTimeZoneOffset(date, -480);
+  assertEquals(result, '2023-10-02T07:00:00+08:00');
+});

dateToIS08601WithTimeZoneOffset.ts

@@ -19,7 +19,10 @@ export const dateToIS08601WithTimeZoneOffset = (
 
   // Thanks, Obama! https://stackoverflow.com/questions/17415579/how-to-iso-8601-format-a-date-with-timezone-offset-in-javascript
 
-  const offset = timeZoneOffset ?? date.getTimezoneOffset();
+  const actualOffset = date.getTimezoneOffset();
+  const offset = timeZoneOffset ?? actualOffset;
+  const difference = offset - actualOffset;
+  const offsetDate = new Date(date.getTime() - (difference * 60 * 1000));
 
   const tzo = -offset;
   const dif = tzo >= 0 ? '+' : '-';
@@ -30,17 +33,17 @@ export const dateToIS08601WithTimeZoneOffset = (
   };
 
   return (
-    date.getFullYear()
+    offsetDate.getFullYear()
     + '-'
-    + pad(date.getMonth() + 1)
+    + pad(offsetDate.getMonth() + 1)
     + '-'
-    + pad(date.getDate())
+    + pad(offsetDate.getDate())
     + 'T'
-    + pad(date.getHours())
+    + pad(offsetDate.getHours())
     + ':'
-    + pad(date.getMinutes())
+    + pad(offsetDate.getMinutes())
     + ':'
-    + pad(date.getSeconds())
+    + pad(offsetDate.getSeconds())
     + dif
     + pad(tzo / 60)
     + ':'