Why are only a few TimeZones available in Blazor WASM?

Question

In Blazor WASM only a few time zones seem to be available when using TimeZoneInfo.GetSystemTimeZones(). Why is that and what controls which they are?

@page "/"

<h1>Hello, world!</h1>

Welcome to your new app.

<SurveyPrompt Title="How is Blazor working for you?" />

<p>@((MarkupString)message)</p>

@code
{
    private string message = "";

    protected override void OnInitialized()
    {
        base.OnInitialized();

        List<string> timeZones = new();
        foreach (var tz in TimeZoneInfo.GetSystemTimeZones())
            timeZones.Add($"Tz DispName:{tz.DisplayName}, StdName:{tz.StandardName}, Id:{tz.Id}");

        message = string.Join("<br/>", timeZones);
    }
}

I get 14 time zones when running the above. When I do something similar in a console app I get approx. 140 time zones. My Win10 machine is configured for Denmark/Europe.

Answer 1

I resolved my issue by introducing a helper class holding the serialization strings of all time zones available on my machine. So, instead of obtaining a TimeZoneInfo object using TimeZoneInfo.FindSystemTimeZoneById I can now use TimeZoneHelper.FindTimeZone in the Blazor WASM client. It enlarges the payload a bit - but it's not an issue in my case.

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;

namespace Utils
{
  public static class TimeZoneHelper
  {
    public static ReadOnlyDictionary<string, string> Data { get; } = new(new Dictionary<string, string>
    {
      { "Dateline Standard Time", "Dateline Standard Time;-720;(UTC-12:00) International Date Line West;Dateline Standard Time;Dateline Daylight Time;;" },
      { "UTC-11", "UTC-11;-660;(UTC-11:00) Coordinated Universal Time-11;UTC-11;UTC-11;;" },
      { "Hawaiian Standard Time", "Hawaiian Standard Time;-600;(UTC-10:00) Hawaii;Hawaiian Standard Time;Hawaiian Daylight Time;;" },
      { "Alaskan Standard Time", "Alaskan Standard Time;-540;(UTC-09:00) Alaska;Alaskan Standard Time;Alaskan Daylight Time;[01:01:0001;12:31:2006;60;[0;02:00:00;4;1;0;];[0;02:00:00;10;5;0;];][01:01:2007;12:31:9999;60;[0;02:00:00;3;2;0;];[0;02:00:00;11;1;0;];];" },
      { "UTC-09", "UTC-09;-540;(UTC-09:00) Coordinated Universal Time-09;UTC-09;UTC-09;;" },
      { "Pacific Standard Time (Mexico)", "Pacific Standard Time (Mexico);-480;(UTC-08:00) Baja California;Pacific Standard Time (Mexico);Pacific Daylight Time (Mexico);[01:01:0001;12:31:2009;60;[0;02:00:00;4;1;0;];[0;02:00:00;10;5;0;];][01:01:2010;12:31:9999;60;[0;02:00:00;3;2;0;];[0;02:00:00;11;1;0;];];" },
      { "Pacific Standard Time", "Pacific Standard Time;-480;(UTC-08:00) Pacific Time (US & Canada);Pacific Standard Time;Pacific Daylight Time;[01:01:0001;12:31:2006;60;[0;02:00:00;4;1;0;];[0;02:00:00;10;5;0;];][01:01:2007;12:31:9999;60;[0;02:00:00;3;2;0;];[0;02:00:00;11;1;0;];];" },
      { "Central America Standard Time", "Central America Standard Time;-360;(UTC-06:00) Central America;Central America Standard Time;Central America Daylight Time;;" },
      { "Central Standard Time", "Central Standard Time;-360;(UTC-06:00) Central Time (US & Canada);Central Standard Time;Central Daylight Time;[01:01:0001;12:31:2006;60;[0;02:00:00;4;1;0;];[0;02:00:00;10;5;0;];][01:01:2007;12:31:9999;60;[0;02:00:00;3;2;0;];[0;02:00:00;11;1;0;];];" },

      // Shortened. Generate and paste full content using:
      //   foreach (var tz in TimeZoneInfo.GetSystemTimeZones())
      //     Console.WriteLine($"{{ \"{tz.Id}\", \"{tz.ToSerializedString()}\" }},");

    });

    public static TimeZoneInfo FindTimeZone(string id)
    {
      if (id == null)
        throw new ArgumentNullException(nameof(id));
     
      if (!Data.TryGetValue(id, out string data))
        throw new TimeZoneNotFoundException("Unknown time zone id: " + id);

      var tz = TimeZoneInfo.FromSerializedString(data);
      return tz;
    }
  }
}