[...Array(5).keys()] not working in Android

[James2516]

Is this a bug report?

Yes

Have you read the Contributing Guidelines?

Yes

Environment

OS: macOS Sierra 10.12.6
Node: 9.8.0
Yarn: 1.5.1
npm: 5.6.0
Watchman: 4.7.0
Xcode: Xcode 9.2 Build version 9C40b
Android Studio: 3.0 AI-171.4443003

Packages: (wanted => installed)
react: ^16.3.0-alpha.1 => 16.3.0-alpha.2
react-native: 0.54.2 => 0.54.2

Steps to Reproduce

console.log([...Array(2).keys()]) does not produce [0, 1].

1. Run https://snack.expo.io/SJT6PCPPZ on Android (works)
2. Run https://snack.expo.io/H1elODwPb on Android (nothing rendered on screen)
   Additional note: both works on iOS.

Expected Behavior

https://snack.expo.io/H1elODwPb should render data on screen

Actual Behavior

https://snack.expo.io/H1elODwPb renders nothing on screen

Reproducible Demo

see above

[react-native-bot]

Thanks for posting this! It looks like your issue may be missing some necessary information. Can you run react-native info and edit your issue to include these results under the Environment section?

Thank you for your contributions.

[hramos]

Seems like a JavaScriptCore issue (this is the JavaScript engine used by React Native).

As a point of comparison, using V8 we get identical results:

[...Array(5).keys()].map(String)
(5) ["0", "1", "2", "3", "4"]
['0', '1', '2', '3', '4'].map(String)
(5) ["0", "1", "2", "3", "4"]

IIRC, we use a fork of the JSC on Android which diverged from what iOS provides.

[guhungry]

I also found this problem on Android.
When I turn off 'Remote JS Debugging' it shows as [].
But when I turn on 'Remote JS Debugging' it shows [0, 1, 2, 3, 4].


PS. iOS always work

[hramos]

You're using a different JavaScript engine when remote JS debugging is turned on - possibly Chrome's (V8).

[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.

[James2516]

still not fixed.

[sonaye]

Workaround:

Array(5).fill().map((_, index) => index)

[ghost]

Workaround by @sonaye works properly, but issue is still not fixed.

[liuqiang1357]

Still not fixed in 0.57

[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.

[James2516]

not yet fixed

[waveChand]

Not yet fixed. still happens when remote debugging turned off.

[hramos]

The JSC in Android was updated in December, it's in master. The new JSC will be part of the 0.59 release. Can you verify on master and let us know if it's still an issue?

[guhungry]

alert([...Array(2).keys()]) works in 0.59.0