Regression on Date.getHours() on node v10.4.1

[germain-gg]

• Version: 10.4.1
• Platform: Darwin 17.5.0 Darwin Kernel Version 17.5.0: Fri Apr 13 19:32:32 PDT 2018; root:xnu-4570.51.2~1/RELEASE_X86_64 x86_64

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I have recently upgraded to node v10.4.1, we were running on v10.3.0 before but decided to upgrade due to https://nodejs.org/en/blog/vulnerability/june-2018-security-releases/

It seems like there is a regression on the Date object with timezone.

const d1 = new Date(1);
console.log(d1.getHours()); // outputs 1

The expected output is 0. When running v10.3.0, the code above outputs 0.

I am located in London, which means that my timezone is BST (British Summer Time). My computer date/time is correct, it is connected to Apple's NTP server (time.euro.apple.com)

Not sure what other info would be relevant for you to solve this issue. Let me know if you need anything from me.

[addaleax]

@nodejs/v8

[addaleax]

Also, this is an issue with v10.4.0 as well, so it’s not the V8 timezone patch we included in v10.4.1.

[bnoordhuis]

We upgraded from V8 6.6 to 6.7 and 6.7 has correcter timezone handling (it delegates it to ICU.)

The expected output is 0.

Can you explain why?

[germain-gg]

@bnoordhuis I don't really have any data to back this up, but it is the behaviour in a lot of previous node versions, I just tested v10.3.0, v9.5.0, v8.0.0 and they all output 0. Hence me assuming that it is the expected output.

[AyushG3112]

According to the MDN docs:

The getHours() method returns the hour for the specified date, according to local time.

Since BST(British Summer Time) is UTC + 1, new Date(1).getHours() most probably adds your timezone offset hours to give you 1.

To get the UTC hours without the timezone offset, you should use getUTCHours instead of getHours.

[germain-gg]

@AyushG3112 Yep definitely agree with you, getHours() is locale dependent. However What puzzles me is that every older version has a different behaviour?

[AyushG3112]

@gsouquet According to what @bnoordhuis said

We upgraded from V8 6.6 to 6.7 and 6.7 has correcter timezone handling (it delegates it to ICU.)

And V8 6.7 landed in Node.js v10.4.0, you can see the relevent PR for V8 here: #19989

This means that any release before v10.4.0 handles timezones differently than v10.4.0 and later do.

[Debugreality]

As an extra note I'm using Node 8.11 in UTC+10 and getHours() returns one hour more than it should, toLocaleString() returns the correct time - this is from a date initiated with an ISODate string:

New Date(new Date().toISOString()).getHours() - 17
New Date(new Date().toISOString()).toLocaleString() - '2018-6-19 16:05:41'

The above code in Chrome returns 16.

Hopefully v10.4 will fix this when I get around to upgrading!