dates() method duplicates dates in period with daylight time switch about instadate

[herkyl]

Could you please write an example of how to replicate it

[max-mykhailenko]

Problem was in date object.
new Date('2016/10/01 00:00:00') — works wrong (switch timezone — correct)
new Date(2016, 10, 1, 0, 0, 0) — works correct (doesn't switch timezone — wrong?)

Can you advise some overall rules for working with Date object?

https://jsbin.com/pojeveratu/edit?js,console

[herkyl]

Date timezone is in the local timezone of the user. I recommend not using 00:00:00 times since you can lose a day due to daylight saving time. You can use instadate.noon to prevent that.

[max-mykhailenko]

So I should to parse time string like 2016/10/01 14:33:13 and set every parameter as argument of new Date() for correct work? How I can create Date from string without parsing and without incorrect timezone behaviour?

[herkyl]

From where are you getting the dates? You can use the ISO 8601 format to safely set them. Most APIs should be returning that. There is no way around the default timezone when using Date (or instadate since it depends heavily on Date). If timezones are important I recommend checking out Moment.js for that part.

If you are generating dates on client-side JS code I recommend creating a base instadate.noon date and using instadate to manipulate that (add days, etc).

Sorry for the late replies btw, I have so many GH notifications that I rarely read them..

[max-mykhailenko]

Oops, I have mistake in example
https://jsbin.com/nudalik/1/edit?js,console
With new Date(2016, 9, 1, 0, 0, 0), I have same mistake in dates array

[max-mykhailenko]

I don't want use timezones, but also I don't want any side effects from them

[herkyl]

What are you trying to do exactly? If you don't care about timezones instadate should work. Why are you trying to use the format 2016/10/01 00:00:00?

[max-mykhailenko]

After using dates()function I expect to get array of unique dates, but I got duplicates :(

[herkyl]

This is because of Daylight savings clock turning on October 30 (http://www.webexhibits.org/daylightsaving/b.html).

You can fix this by using the noon function from instadate:

const dates = instadate.dates(
  instadate.noon(new Date('2016/10/01 00:00:00')),
  instadate.noon(new Date('2016/11/01 00:00:00'))
);

If you are using the 00 hour of the day then daylight saving can shift it to the previous day.

[max-mykhailenko]

But setting to noon ruins my time!

[herkyl]

You have to find a way around it, as it is a limitation of the JS Date.

[max-mykhailenko]

But you can avoid this situation, just don't use 24 hours constant as day length. Instead you can use a function like

function addDays(date, days) {
    var result = new Date(date);
    result.setDate(result.getDate() + days);
    return result;
}

[herkyl]

I added tests for the edge case as well as changed all of the adding functions in ce0352a and published it on npm as 0.3.1.

Now I wonder if differenceInX functions also have that issue. Need to check those later.

Let me know if this fixes your issue

[max-mykhailenko]

Thanks! It's great, I'll test it on this week