Date instance on eve of the beginning of daylight savings returns hour behind (Android)

[jgitt]

Environment - react-native info

  React Native Environment Info:
    System:
      OS: Windows 10
      CPU: x64 Intel(R) Core(TM) i7-8550U CPU @ 1.80GHz
      Memory: 6.80 GB / 15.86 GB
    Binaries:
      npm: 5.6.0 - C:\Program Files\nodejs\npm.CMD
    IDEs:
      Android Studio: Version  3.1.0.0 AI-173.4907809

Other Environment Details

React: 16.5.0
React-native: 0.57.2
Timezone: AEDT - Australian Eastern Daylight Time
Device: Android 8.0 (API 26). Running in emulator (Genymotion). Have briefly tested on device, while it wasn't as thorough, it did show same issue.

Description

Creating a Date instance on the eve of daylight savings starting in Australian Eastern (Daylight) Time returns the hour as an hour behind. Only tested on Android.

The following line is expected to print 20, however it shows 19.

new Date(2018, 9, 6, 20, 0).getHours()

In browser (latest Chrome) and Nodejs (8.11.4) the above line returns 20.

I did further testing with the following timezones using the eve of the respective day light savings date and they did not show the same issue.

• PDT (GMT-7)
• EDT (GMT-4)

Reproducible Demo

1. Create new react app via react-native init DateIssueTest
2. (I had an issue with starting so did react-native start --reset-cache)
3. react-native run-android
4. Modified App.js to include:

        <Text style={styles.instructions}>{new Date(2018, 9, 5, 20, 0).getHours()}</Text>
        <Text style={styles.instructions}>{new Date(2018, 9, 6, 20, 0).getHours()}</Text>
        <Text style={styles.instructions}>{new Date(2018, 9, 7, 20, 0).getHours()}</Text>

5. The device timezone must be Australian Eastern (Daylight) Time (i.e. Sydney). So Settings > System > Date & time > Select time zone > Sydney
6. It's expected that each line of code above should show 20, however in my test, the middle line shows 19

[nathan-k]

Possibly related to this: https://bugs.webkit.org/show_bug.cgi?id=137003

[kelset]

Yes, it seems that it's potentially related to the WebKit - sadly at the moment React Native ships on Android with an old version of the JSC; as workarounds I think you can try using:

• a library such as moment (it worked for me in the past in this kind of scenario)
• a custom JSC like https://github.com/react-community/jsc-android-buildscripts

With version 0.58 we are planning on making it easier to move to a newer JSC but at the moment is not easily achievable.

[jgitt]

No problem. Thanks @kelset. I'm using DayJS and it still shows the same problem, but I'll give Moment a shot.

[stale]

Hey there, it looks like there has been no activity on this issue recently. Has the issue been fixed, or does it still require the community's attention? This issue may be closed if no further activity occurs. You may also label this issue as "For Discussion" or "Good first issue" and I will leave it open. Thank you for your contributions.

[hramos]

The new JSC landed on master a month ago.