This is an important comment note that I use only occasionally in ReactNative.

Installing react-native-cli globally with npm

npm install -g react-native-cli
react-native -v

Create a project
Be careful not to use the same name as a Sample(react-native init Sample) or something else used internally such as ReactNative, because it seems to give an error.

react-native init ReactNative

Launching the ios emulator.

cd ReactNative
react-native run-ios