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Fix issue #182: wrong offset within 1hr of DST start #233

Merged
merged 2 commits into from
Oct 28, 2020
Merged

Fix issue #182: wrong offset within 1hr of DST start #233

merged 2 commits into from
Oct 28, 2020

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bsvetlik
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Solved the Chicken and Egg Problem described in summerTime.js: "we can't get the date, without knowing the timezone, and vice-versa".
In order to eliminate the time zone offset effect the given UTC time is compared to the DST change boundaries converted to UTC.

spencermountain and others added 2 commits September 14, 2020 16:58
@spencermountain
Merge pull request spencermountain#228 from spencermountain/dev
14fd1ef 
Dev
@bsvetlik
Fix issue spencermountain#182: wrong offset within 1hr of DST start
a9f2acd 
Solved to Chicken and Egg Problem described in summerTime.js: "we can't get the date, without knowing the timezone, and vice-versa".
In order to eliminate the time zone offset effect the given UTC time is compared to the DST change boundaries converted to UTC.
@spencermountain spencermountain changed the base branch from master to dev October 28, 2020 15:31
@spencermountain
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holy crap!
i would hug you if I could.
gonna merge this into develop and throw a bunch of tests at it - I guess the trick is using Date.UTC()?
That is an extremely clever solution.
WIll play-around with this this afternoon, and check back.
Thank you, so much.

@spencermountain spencermountain merged commit e2b9df9 into spencermountain:dev Oct 28, 2020
@bsvetlik
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Hi,
I'm glad I was able to help!
A few days ago I solved the similar problem: change JS Date object to show time in another time zone. I evaluated a number of date-time libraries that support DST changes (moment, luxon, date-fns-tz) but they were amazingly slow (0.5sec for 10,000 conversions). I had to find other solution: given the specific time zone offsets with DST change boundaries received from the server as UTC milliseconds shift the time by corresponding offset. I developed an algorithm that was much faster (15 milliseconds for 10,000 conversions). The spacetime library issue #182 was similar to my problem. The only difference was the DST change boundaries in the specific time zone. After converting them to UTC the Chicken and Egg problem (I liked your description - it was in tune with my thoughts when I worked on conversion algorithm) was solved!
Regards. Boris.

spencermountain added a commit that referenced this pull request Oct 28, 2020
@spencermountain
add some tests for #233
1a01db7
spencermountain added a commit that referenced this pull request Oct 28, 2020
@spencermountain
now testing north and south hemisphere #233
c9c8d72
spencermountain added a commit that referenced this pull request Oct 28, 2020
@spencermountain
test north hemisphere spring too #233
3b978ea
spencermountain added a commit that referenced this pull request Oct 28, 2020
@spencermountain
more dst tests #233
6862844
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this works amazingly.

published as 6.8.0
🏅

@neutraltone neutraltone mentioned this pull request Oct 30, 2020
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@bsvetlik @spencermountain