I have been working on Ionic 4 project recently and I hit to wall because since Cordova has compatibly issues with the latest Xcode (10). After headaches with compiling the iOS project I returned to great Ionic documentation about iOS setup where it of course clearly says on the top:
We recommend using XCode 9. Xcode 10 support in Cordova is still a work-in-progress. See this issue for details.
So, yes. You need Xcode 9 if you want to work on Corova still (as writing in Feb 8 2019.) Luckily it is possible to run multiple versions of Xcode on the same machine. You simply need to copy additional versions to Applications with different name. Like this:
- Install recommended Xcode that comes with OS
- Go to https://developer.apple.com/download/more/ and download Xcode 9.x
- Unzip and rename Xcode to Xcode9
- Copy Xcode9 to Applications and run it.