Implement isDaylightSavingTime

[inosik]

References #1082.

Because JS doesn't have a native function for this, we need to check if the Dates UTC offset is equal to either the offset in January or in June.

If a users time zone doesn't have DST, this function should always return false.

@alfonsogarciacaro where can I add tests for the isDST function?

[alfonsogarciacaro]

Thanks a lot for this! @forki's test should be enough to check isDaylightSavingTime, do you want to test isDST separately?

[inosik]

I actually wanted to test it with some predefined values, but maybe it's just me being paranoid. 😄

In this case, there's probably no reason to make it a separate function.

[forki]

Don't worry. If it's releasedocs then I will write UI tests for our app starten and test it indirectly ;-) Am 18.07.2017 12:54 schrieb "Ilja Nosik" <notifications@github.com>: I actually wanted to test it with some predefined values, but maybe it's just me being paranoid. 😄 In this case, there's probably no reason to make it a separate function. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#1083 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AADgNMaMPZAIdWwXhwGcDKcswDohPSTiks5sPI76gaJpZM4ObIzV> .

[forki]

@inosik thanks for implementing it.
you win a music video: https://www.youtube.com/watch?v=7aJYK3PnWqU

[inosik]

Sweet! Now I need to win some speakers for my workstation 😄

[alfonsogarciacaro]

This is what I see most of the times when I try to share a video between Germany and Spain ;)

[forki]

sorry guys you are missing out.

[inosik]

Unfortunately, the fix breaks Travis CI. AppVeyor seems to be completely broken right now.

[alfonsogarciacaro]

Luckily my advanced hacker skills prevail over Youtube algorithm... by typing the video title in the Search Bar ;)

[alfonsogarciacaro]

I hate Travis, it's been failing continuously for a while now for not apparent reason 😬

[inosik]

AppVeyor doesn't seem to run at all at the moment, but Travis fails because of the test from #1082.

[inosik]

// index.js
function isDaylightSavingTime(x) {
    var jan = new Date(x.getTimezoneOffset(), 0, 1);
    var jul = new Date(x.getTimezoneOffset(), 6, 1);
    return isDST(jan.getTimezoneOffset(), jul.getTimezoneOffset(), x.getTimezoneOffset());
}

function isDST(janOffset, julOffset, tOffset) {
    return Math.min(janOffset, julOffset) === tOffset;
}

var d1 = new Date(2017, 6, 18, 2, 0, 0);
var d2 = new Date(2017, 11, 18, 2, 0, 0);

console.log(d1.toString() + " is DST: " + isDaylightSavingTime(d1).toString());
console.log(d2.toString() + " is DST: " + isDaylightSavingTime(d2).toString());

$ node index.js
Tue Jul 18 2017 00:00:00 GMT+0200 (Mitteleuropäische Sommerzeit) is DST: true
Mon Dec 18 2017 00:00:00 GMT+0100 (Mitteleuropäische Zeit) is DST: false

Works for me. Must be the time zone of the Travis instance.

[alfonsogarciacaro]

Let's see what Appveyor says and, if necessary, disable that test in the CI servers.

[inosik]

As I wrote in #1082, this test will fail for everybody who runs it in a country without DST. That's why I wanted to test the isDST function instead of DateTime.IsDaylightSavingTime().

Looks like we can control the time zone in Travis CI with the TZ environment variable and in AppVeyor with tzutil, which is a Windows program. But I don't think that it's a good idea to rely on this.

[forki]

can ask for the current zone? we might then just enable US, Germany and that's it