How to display the time in user’s timezone

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Rails by default converts every date into UTC before storing the value into the database. This means that, regardless the server timezone, you always have UTC dates in your database.

In order to convert the dates into your user’s timezone you have basically two possibilities:

  1. server-side approach
  2. client-side approach

Server-side approach

If your site allows registration, you can store the user timezone as user preference. In the user table, store the user timezone. Then create a custom helper you can use to format any date/time into the proper timezone using the in_time_zone method.

> t = Time.current
# => Mon, 23 Dec 2013 18:25:55 UTC +00:00 
> t.zone
# => "UTC" 
> t.in_time_zone("CET")
# => Mon, 23 Dec 2013 19:25:55 CET +01:00

Your helper may looks like

def format_time(time, timezone)
  time.in_time_zone(timezone)
end

I normally also like to output a standard format, using the I18n.l helper

def format_time(time, timezone)
  I18n.l time.to_time.in_time_zone(timezone), format: :long
end

Client-side approach

If your site has no registration or you don’t want to ask your users for their timezone or you simply want to use the user system timezone, then you can use JavaScript.

My suggestion is to create a custom helper that will print out every time in a proper way so that you can create a generic JavaScript function to convert the values.

def format_time(time, timezone)
  time = time.to_time
  content_tag(:span, I18n.l(time, format: :long), data: { timezone: timezone, time: time.iso8601 })
end

Now, create a JavaScript function that is performed on DOM load and that will select all the HTML tags with data-time attribute. Loop them and update the value inside the span tag with the proper time in the given timezone.

A simple jQuery example would be

$(function() {
    $("span[data-time]").each(function() {
        // get the value from data-time and format according to data-timezone
        // write the content back into the span tag
    });
});

I’m not posting the full code here, since there are plenty of JavaScript time formatters available with a simple search. Here’s a few possible solutions

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