IE11: Cannot load Array[Symbol.iterator] polyfill

[compulim]

Version

master

Describe the bug

It seems core-js is loaded incorrectly. This is causing sagas/effects/forkPut.js to fail after Webpack in IE11. This bug is introduced when we bump core-js@2 to core-js@3 in PR #2195, because core-js@3 changed the import signature.

Instead of loading using import 'core-js/modules/es.symbol', we should load it using import 'core-js/features/symbol'.

I believe when we load from /features/ instead of /modules/, these features are aware of each other. For example, "symbol" is aware of "array.iterator" and complement each other. But when we are loading from /modules/, they do not aware of each other.

To Reproduce

Steps to reproduce the behavior:

1. Create a create-react-app
   • No need to install Web Chat, we are just proving the polyfill is loaded incorrectly
2. Copy the polyfill code from index-es5.ts to the app
   • This include all imports starting with core-js from https://github.com/microsoft/BotFramework-WebChat/blob/master/packages/bundle/src/index-es5.ts#L8
3. Run npm run build
   • CRA development build do not work with IE11, it only works with production build
4. Host the app
5. On IE11, browse to http://localhost:3000/
6. In the console, run new Array()[Symbol.iterator]

Expected behavior

After running the code, it should return a function, polyfilled by core-js.

Instead, it is returning undefined.

Additional context

[Bug]