Set.size is broken on ReactNative for Android

[gusbicalho]

Description

When running a ReactNative app on Android, a Set from core-js always return an undefined size, while the native Set implementation works fine.

The problem does not show up when debugging the Android app I think this is because in debug mode the JS code runs in the Chrome debugger (V8), while normally it runs in the JavaScriptCore engine.

The problem also does not show up when running on iOS simulator, which suggests it's some compatibility issue with the specific implementation of JavaScriptCore used on Android. I wasn't able to test on a real iOS device.

Running tests with jest (which runs on Node) also shows no problem.

Steps to reproduce:

• clone https://github.com/gusbicalho/RNSetTest
• npm install
• open an android emulator
• npm run android

[gusbicalho]

Found the cause:
The base Set implementation in ReactNative#android defines set as a property of each Set object, instead of defining it on the prototype, so this check https://github.com/zloirock/core-js/blob/master/library/modules/_collection.js#L44 fails.

Not sure how to fix that, though.