web: fix dateTimeLocal() dropping local timezone

closes #2860

Signed-off-by: Jens Langhammer <jens.langhammer@beryju.org>

web/src/utils.ts

@@ -97,6 +97,10 @@ export function dateTimeLocal(date: Date): string {
     // milliseconds, which the input field doesn't like (on chrome, on firefox its fine)
     // On chrome, setting .valueAsNumber works, but that causes an error on firefox, so go
     // figure.
-    const parts = date.toISOString().split(":");
+    // Additionally, toISOString always returns the date without timezone, which we would like
+    // to include for better usability
+    const tzOffset = new Date().getTimezoneOffset() * 60000; //offset in milliseconds
+    const localISOTime = new Date(date.getTime() - tzOffset).toISOString().slice(0, -1);
+    const parts = localISOTime.split(":");
     return `${parts[0]}:${parts[1]}`;
 }