I’ve recently been heavily embedded in implementing time zone sensitivity into a web application and I thought I’d share my first experiences on handling this from the perspective of the browser.

A great little library for handling this kind of tricky number can be found in the form of Moment Timezone, which sits proudly beside Moment.js, but as a full date parsing solution incorporating time zones.

The part of the library that really caught my attention was the time zone inferring abilities of the library; the superbly named ‘guess‘ function (loving the name!). The function, despite the name, is actually pretty sophisticated, so let’s take a look at a working example and how the documentation defines the ‘guts’ of its time zone guessing powers.

Moment Timezone can be installed and used in a number of different ways, as described here, but I went with the good old classic method of adding a NuGet package via Visual Studio:

Or, if you want to use the Package Manager Console then use this nugget instead:

Install-Package Moment.Timezone.js

Once the package is installed, alive and kicking we need to (as you would expect) reference the supporting Moment JavaScript library followed by the Moment Timezone based library, as follows:

<script src="~/Scripts/moment.min.js" type="text/javascript"></script>
<script src="~/Scripts/moment-timezone-with-data.min.js" type="text/javascript"></script>

You are then ready to utilise the guess function in a stupendous one-liner, just like this (wrapped in a jQuery document ready function, in this example):

<script type="text/javascript">
    // On page load grab a value denoting the time zone of the browser
    $(function () {
        // Log to the console the result of the call to moment.tz.guess()
        console.log(moment.tz.guess());
    });
</script>

The screenshots listed here show just a few examples of how the guess function works (by providing a tz database, or IANA database, value denoting which time zone Moment Timezone has inferred the client is in).

For newer, supporting browsers, Moment Timezone can utilise the Internationalization API (Intl.DateTimeFormat().resolvedOptions().timeZone) to obtain time zone information from the browser. For other browsers, Moment Timezone will gather data for a handful of moments from around the current year, using Date#getTimezoneOffset and Date#toString, to intelligently infer as much about the user’s environment as possible. From this information, a comparison is made against entries in the time zone database and the best match is returned. The most interesting part of this process is what happens in the case of a tied match; in this instance, a cities population becomes a deciding factor (the time zone linking to a city with the largest population is returned).

A full listing of tz database values can be found using the link below, showing the range of options available including historical time zones. It’s worth noting that the tz database also forms the backbone of the very popular Joda-Time and Noda Time date/time and timezone handling libraries (Java and C#, respectively; from the legendary Mr Skeet!).

List of tz database zones

For the project I was involved with, I ended up using Noda Time to actually perform conversions server side, utilising Moment Timezone to provide a ‘best stab’ at a user’s timezone on first access of the system. I’d like to give this the attention it deserves in a follow-up post.

Have a great week everyone, until the next time!