TZ.js

Built for plate; determines (roughly) the timezone name based on a few lovely factors. Adds two prototype methods to Date.

Date.prototype.tzoffset

Get a formated, GMT+0000-style offset string for your locale, based on the result of Date.prototype.getTimezoneOffset.

Date.prototype.tzinfo()

Returns an object with the following information if tzinfo exists for your locale's offset (as returned by Date.prototype.getTimezoneOffset):

    {
          'name'  : 'Human Readable Name of Area'
        , 'loc'   : 'Location of TZ: E.G., North America'
        , 'abbr'  : 'shortname for tz: E.G, CST'
        , 'offset': '(+|-)0XXX'
    }

The TZINFO is collected in tz.json.

How does it work?

Fuzzily. A list of known TZ data is stored in tz.json, keyed by offset (+0000, -0600). The ordering of the list is important. Roughly, the algorithm does the following:

• Get the offset string from your date.

• Lookup the list of TZ's corresponding to that offset.

• Determine whether your timezone has Daylight Savings.

• Determine the thresholds at which Daylight Savings Time takes effect in your locale, if any.

• Determine, based on that, whether your locale is in the northern or southern hemisphere. Default to southern hemisphere.

  How does that work?

  If you're in the northern hemisphere, the threshold for "spring forward" will be earlier than "fall back".

  In the south, this is reversed.

• If your locale is currently in DST, filter the TZ list for names that match /([Dd]aylight|[Ss]ummer)/.

• If your locale is in the south (or we have no DST info), reverse the list.

• Return the first time from that list as the TZinfo.

  Why default to the south?

  For countries that have DST, we can easily determine which half of the Earth they're on. For countries that don't, we're forced to guess. However, if we approach from the South, we tend to pick up countries of interest.

Install (in browser)

$ git clone [email protected]:chrisdickinson/tz.js.git
$ cd tz.js
$ make build
$ # now you have tz.js, and if you have uglifyjs or jsmin, you also have tz.min.js

Install (in node)

npm install tz

Run the tests

npm install --dev tz; npm test tz

License

MIT