1514677 - getHours on Date with DST before 1980 returns wrong value

Status: RESOLVED DUPLICATE of bug 1346211

(Core :: JavaScript Engine, defect)

Description

[maddin.schuetz]

User Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36

Steps to reproduce:

Calling getHours on a Date with DST before 1980 returns a wrong value on a machine with german timezone.
In Germany before 1980 there was no DST.




Actual results:

new Date("1977-07-03T01:11:27.822Z").getHours() returns 3


Expected results:

new Date("1977-07-03T01:11:27.822Z").getHours() returns 2

The function toLocaleTimeString returns the right value.
This jasmine test fails in Firefox, in other browsers it works:
it("this test fails", () => {
            const dat = new Date("1977-07-03T01:11:27.822Z");
            expect(dat.getHours()).toEqual(+dat.toLocaleTimeString(undefined, { hour: "2-digit" }).substr(0, 2));
        });

Comment 1

[maddin.schuetz]

Found another case:
Dates between 1980 and 1996. In this time in germany the DST lasted only until september, not until october as most other states in EU.

So this test also fails:
it("this test fails too", () => {
            const dat = new Date("1995-09-28T01:11:27.822Z");
            expect(dat.getHours()).toEqual(+dat.toLocaleTimeString(undefined, { hour: "2-digit" }).substr(0, 2));
        });

It works with a year >= 1996

Comment 2

[André Bargull [:anba]]

Starting with Firefox 63 (bug 1346211), we're using more accurate historical time zone data. Before Firefox 63, the POSIX API of the underlying OS was queried for any time zone computation, which means on Windows only the current time zone rules were applied. This should explain the results in comment #0 and comment #1, because both reflect the current EU rules instead of the time zone rules in Germany at that point of time.

So basically updating to a more recent Firefox version should fix the issue.

Comment 3

[maddin.schuetz]

Thank you :anba the tests work in Firefox 64

Comment 4

[André Bargull [:anba]]

Great, thanks for verifying!