[Android] es6 Polyfills

[Thomas101]

Hey,

I've found a few es6 polyfils which behave differently to how they should on android. They work fine on iOS and work fine when you run on android with debug enabled.

var s = new Set([1,2,3]) // New set created with one item (the array). Should contain 3. Works if you pass in 3 arguments
var a = Array.from(new Set([1])) // creates an empty array rather than [1,2,3]

var m = new Map()
m.set('k', 'v')
var iter = m.keys()
iter.next() // iter.next is undefined. Same for m.values() and m.entries()

Tom

[facebook-github-bot]

Hey Thomas101, thanks for reporting this issue!

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[atom992]

+1

[christopherdro]

/cc @satya164 @janicduplessis

[satya164]

cc @skevy also

[janicduplessis]

This probably happens because we use an older version of JSC on android. There's probably a bad or missing polyfill for Map/Set/Iterator

[bsy]

+1, any updates on this?

array.entries() doesn't work on android, RN 0.27.2

[satya164]

@bsy Feel free to send a PR if this is important to you.

[mkonicek]

Hi there! This issue is being closed because it has been inactive for a while.

But don't worry, it will live on with ProductPains! Check out its new home: https://productpains.com/post/react-native/android-es6-polyfills

Product Pains has been very useful in highlighting the top bugs and feature requests:
https://productpains.com/product/react-native?tab=top

Also, if this issue is a bug, please consider sending a pull request with a fix.

[eduardojunio]

@Thomas101 did you found someway to workaround this issue? I'm having the same problem with TypedArrays, works perfectly on iOS, but not on Android.

"react-native": "0.47.1", "react": "16.0.0-alpha.12"

[Thomas101]

@eduardojunio never got around to fixing it to be honest. Due to time constraints we just avoided using the affected methods. e.g.

const set = new Set()
const arr = [1,2,3]
arr.forEach((v) => set.add(v))

rather than new Set([1,2,3])

[eduardojunio]

@Thomas101 I managed to workaround this by including import 'core-js' in the file that is using the typed array (thanks to this issue #4676 (comment)).

[chirag04]

i was able to replicate. reopening but feel free to send a PR

[luco]

@eduardojunio I couldn't fix it by adding core-js on the file. Is there any further step?
My app still crashing on for loops.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Maybe the issue has been fixed in a recent release, or perhaps it is not affecting a lot of people. If you think this issue should definitely remain open, please let us know why. Thank you for your contributions.

[ericketts]

oh wise stale bot, I petition this issue being re-opened, as it is still occurring for me on react-native 0.53-rc.1 with react 16.2.0.

Also worth noting this issue is not solved by using core-js (I'm on version 2.5.3), as per this ticket of theirs zloirock/core-js#368

[jalooc]

Yes, this issue is still on - shouldn't have been closed. @chrisnojima described the source of this problem really well in zloirock/core-js#368 (comment) (seems to be a problem with babel/core-js). What's worth mentioning: it doesn't happen during remote debugging.

Just a note from my experience with this bug: In my app it's caused when using viewabilityConfigCallbackPairs in FlatList. Reverting core-js to 2.5.2 didn't help.

---

One more interesting observation, that may be connected to this issue, is that I get the following warnings only when not remote debugging:

• Warning: React.createElement: type is invalid -- expected ... but got: object
  

  ^ with stack trace pointing to <Fragment>, where Fragment is imported in a legitimate way:
  import React, { PureComponent, Fragment } from 'react' (with v0.53, where fragments' support has already landed);

• Warning: Each child in an array or iterator should have a unique "key" prop ...
  

  ^ this pointed to children of aforementioned <Fragment>.

I don't know about it, but seems a bit like other versions of packages where used during remote debugging then during non-remote debugging...