React Native Array.reverse bug

This is an example app to demonstrate that the Array.reverse bug for iOS 12 exists in React Native as well.

Some have called to calling this a "Safari bug", but that is misleading. The bug exists in the JavascriptCore-framework for iOS, which several other apps/frameworks depend upon, React Native among them.

Buggy-check code borrowed from the array-reverse-polyfill-package:

var a = [1, 2];
return String(a) === String(a.reverse());

Using this example

If you have Xcode + React Native dependencies installed, from terminal run:

git clone git@github.com:cbrevik/arrayReverseBug.git
cd arrayReverseBug
yarn install
react-native run-ios --device "The name of your iPhone with iOS 12"

This example will also work using iOS simulator if you have Xcode 10+.

Screenshots

If your device/simulator is running iOS 12, the following should be displayed:

Important! If the React Native remote debugger is attached, the bug will not occur.

This is because the remote debugger uses Chrome, instead of JavascriptCore:

Links

• https://news.ycombinator.com/item?id=18021835
• https://stackoverflow.com/a/52394459/5703116
• https://bugs.webkit.org/show_bug.cgi?id=188794
• https://www.npmjs.com/package/array-reverse-polyfill