DST issue

[Darrken]

Daylight Savings Time seems to be an issue in the plugin.

    let utcDate = dayjs("2016-11-18:00:00:00+00:00");
    console.log(utcDate.utc().format());  // 2016-11-17T23:00:00+00:00

I'd expect 2016-11-18T00:00:00+00:00 to be the value returned.
I found that dates including and between 11/7 - 3/13 have this problem.

Or am I just missing something? (My local offset is -7, observing DST currently.)

[myfrom]

I'm not sure but from what I've been testing this might be caused because the script always gets the current time offset, not time offset from the specified date.

For example, based on where I am:
I'm in DST now, new Date().getTimezoneOffset() will return -120.
But if I give it a date outside of DST, new Date(27600000).getTimezoneOffset() will return -60.
So in such case, it subtracts two hours from the date instead of one.

I think LOCAL_TIMEZONE_OFFSET should be set dynamically. But as I'm not familiar with the code I might be wrong, what do you think?

[Farkal]

Same issue here.
I am in France in august we were UTC+2 and now we are UTC+1.
If I try to convert august timestamp to utc date the hour is just subtracted by one instead of 2.

import dayjs from 'dayjs'
import dayjsPluginUTC from 'dayjs-plugin-utc';

dayjs.extend(dayjsPluginUTC);

const time = '1533722400'

const d = dayjs.unix(time).utc().format()
console.log(d)  // 2018-08-08T11:00:00+00:00 supposed to be 2018-08-08T10:00:00+00:00

const d2 = new Date(time * 1000).getTimezoneOffset()

console.log(d2)  // -120

[danazkari]

I think there's a way to help with DST calculations but it would NOT work on IE11, would that be a problem? If not, I can come up with a PR within the next few days.

[guisturdy]

I think there's a way to help with DST calculations but it would NOT work on IE11, would that be a problem? If not, I can come up with a PR within the next few days.

with what reason it would not work on IE11?

[dgrelaud]

If you have some issues with DST and DaysJS, try my dayjs plugin:
https://www.npmjs.com/package/dayjs-timezone-iana-plugin

cf. comment: iamkun/dayjs#1271 (comment)