Check out this link (Running react-native run-ios occurs an error?). It appears to be a problem with the location of
Command line tools.
In Xcode, select Xcode menu, then Preferences, then Locations tab. Select your Xcode version from the dropdown and exit Xcode.
You may need to install or set the location of the Xcode Command Line Tools.
Via command line
If you have Xcode downloaded you can run the following to set the path:
sudo xcode-select -s /Applications/Xcode.app
If the command line tools havent been installed yet, you may need to run this first:
You may need to accept the Xcode license before installing command line tools:
sudo xcodebuild -license accept
Or adjust the
Command Line Tools setting via Xcode (
Xcode > Preferences > Locations):
By default, after installing Xcode command-line not selected, so open Xcode and go to Preferences >> Locations and set Command Line Tools…
This worked for me in MAC High Sierra, Xcode Version 9.3:
i to open iOS emulator…
And You can see a cool new iPhone simulator like below image: