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Comment by ryndshn | Hacker News Reader

if i remember correctly, Airbnb had many issues with RN that were not related to their incremental migration, such as the issues they had with things like debugging, where it was almost impossible to fix certain bugs due to RN using different JS engines depending on platform and context (for ex running with a debugger causes RN to use V8 whereas running locally on iOS / Android it uses JavaScriptCore or Hermes, respectively). RN is awesome but imo has some pretty serious pain points.

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RN used to have a lot of issues years ago (~2015-2016 or so) with different layout rendering between iOS and Android. Since they re-wrote their layout engine to be the same codebase across Android and iOS this has been 99% fixed in my experience. You might very occasionally run into a difference of some sort but it will most likely be minor. Of course, I would say if you've never done a RN project before and you plan to release both iOS and Android, please DO test your app frequently on both as you code along. If you complete 90% of the code on, say, iOS only and then try to run it on Android, chances are you'll run into more WTH problems than if you were checking along the way.

none of the issues i described are different now. RN on iOS still uses JavaScriptCore by default, Android uses Hermes, and it still uses V8 if debugging, meaning it's possible you'll have some super weird edge case bugs. in Airbnb's situation i believe they said it was almost impossible to pinpoint the issue due to the differences in these engines. it's unlikely, but still an unavoidable thing that could be a serious roadblock

I've done and ran 2 medium sized apps on both iOS and Android and have never ran into such problems. While not impossible, that's akin to saying that if you run the JVM on MacOS vs Linux, there's a chance of different behavior. Possible, but unlikely. It shouldn't be a show-stopper for most situation.

ehh, not really. JVMs are all developed under the same roof but JS engines are a little more distributed and the spec has a little more room for interpretation. i agree it's unlikely, but still not ideal

Yes, fair enough. Not a perfect analogy.

Hermes runs on iOS now and besides missing Intl, I’ve not had any problems with it and flipper let’s you debug hermes.

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