Get utc offset from timezone in Javascript

javascript timezone datejs

user3124032 · Dec 20, 2013 · Viewed 18.4k times · Source

I need a Javascript function that given a timezone, returns the current utc offset.

For example, theFuncIneed('US/Eastern') -> 240

Any idea?

Thanks

Answer

In general, this is not possible.

US/Eastern is an identifier for a time zone. (It's actually an alias to America/New_York, which is the real identifier.)
240 is a time zone offset. It's more commonly written as -04:00 (Invert the sign, divide by 60).
The US Eastern Time Zone is comprised of both Eastern Standard Time, which has the offset of -05:00 and Eastern Daylight Time, which has the offset of -04:00.

So it is not at all accurate to say US/Eastern = 240. Please read the timezone tag wiki, especially the section titled "Time Zone != Offset".

Now you did ask for the current offset, which is possible. If you supply a date+time reference, then you can resolve this.

For the local time zone of the computer where the javascript code is executing, this is built in with .getTimeZoneOffset() from any instance of a Date object.
But if you want it for a specific time zone, then you will need to use one of the libraries I listed here.