What's the difference between zone.parse and zone.offset

[zhangchiqing]

According to the document, both zone.parse and zone.offset accept a timestamp and return the offset. Why zone.parse and zone.offset print different offset result? What's the difference between them?

var zone = moment.tz.zone('America/New_York')
zone.parse(Date.UTC(2015, 10, 1, 4, 30, 0)); // => 300
zone.offset(Date.UTC(2015, 10, 1, 4, 30, 0)); // => 240

[mattjohnsonpint]

I agree the documentation isn't very clear. The difference is that zone.offset takes a true UTC-based timestamp, while zone.parse takes an timestamp that is based on that particular time zone.

In other words, even though Date.UTC returns the number of milliseconds since 1970-01-01T00:00:00Z, the zone.parse function treats it as if it were the number of milliseconds since either 1970-01-01T00:00:00-05:00 or 1970-01-01T00:00:00-04:00 (for the America/New_York zone), depending on which is in effect for the given timestamp. If the time could exist in both offsets (or can't exist in either), then the rules detailed in Parsing Ambiguities are followed.

[mattjohnsonpint]

IMHO, zone.parse doesn't have many external use cases. I would have expected it to be an internal function, not exposed through the public API.

[mattjohnsonpint]

Also, note that the ambiguous parsing behavior has changed with #101 - and the docs have not yet been updated.

[zhangchiqing]

Cool! Thanks @mj1856 for the explanation :)