til/rails/get-formatted-utc-offset-value.md

Get Formatted UTC Offset Value

The UTC offset (during DST) for Chicago is -05:00. And for Newfoundland it is -02:30.

Rails has an ActiveSupport::TimeZone module that can turn the UTC offset in seconds into this formatted value.

> chicago = TZInfo::Timezone.get('America/Chicago')
=> #<TZInfo::DataTimezone: America/Chicago>
> ActiveSupport::TimeZone.seconds_to_utc_offset(chicago.utc_offset)
=> "-05:00"

> newfoundland = TZInfo::Timezone.get('America/St_Johns')
=> #<TZInfo::DataTimezone: America/St_Johns>
> ActiveSupport::TimeZone.seconds_to_utc_offset(newfoundland.utc_offset)
=> "-02:30"

The underlying tzinfo gem is DST-aware and its database even knows which time zone identifiers don't observe DST, so you can run this anytime of the year and expect reliable results.

Here is another way at this:

> chicago = TZInfo::Timezone.get('America/Chicago')
=> #<TZInfo::DataTimezone: America/Chicago>
> ActiveSupport::TimeZone[chicago.name]
=> #<ActiveSupport::TimeZone:0x00000001099d8140 @name="America/Chicago", @tzinfo=#<TZInfo::DataTimezone: America/Chicago>, @utc_offset=nil>
> ActiveSupport::TimeZone[chicago.name].formatted_offset
=> "-06:00"
> ActiveSupport::TimeZone[chicago.name].formatted_offset(false)
=> "-0600"