javascript - Initialize a Moment with the timezone offset that I created it with

Question

I'm using moment and moment-timezone in javascript, and this part of it is one of the most unintuitive API's I've ever seen.

I would expect that:

moment("2015-12-14T04:00:00Z").utcOffset()

would be a pure function and return the offset included in the argument, which is 0. But instead it implicitly converts it to my local timezone offset (PST), so this returns -480 Why?? I asked what offset the object i just created has, not what offset I'm currently in. It would be like if I wrote an api where calling User.find(123).name() returns your name instead of the name of user 123.

Anyway, I can do

moment("2015-12-14T04:00:00Z").tz("utc").utcOffset()

But my datetime string is dynamic, so I don't know the timezone.

How can I get the behavior I expected, a Moment in js that is in the timezone offset included in the string i passed in?

Answer 1

Use parseZone to keep the offset as it was passed in.

moment.parseZone("2015-12-14T04:00:00Z")

As to the "why?" part of your question:

• moment(...) is local mode. Ambiguous input (without offset) is assumed to be local time. Unambiguous input (with offset) is adjusted to local time.
• moment.utc(...) is utc mode. Ambiguous input is assumed to be UTC. Unambiguous input is adjusted to UTC.
• moment.parseZone() keep the input zone passed in. If the input is ambiguous, it is the same as local mode.
• moment.tz(...) with the moment-timezone plugin can parse input in a specific time zone.

Keep in mind that moment has to contend with a wide variety of inputs.

Also keep in mind that a time zone and a time zone offset are two different things. An offset of -08:00 doesn't necessarily mean you are in the US Pacific time zone.