You are trying to add react-native in other react project. React Native is like React, but it uses native components instead of web components as building blocks. So install react-native using npm install -g react-native-cli in a new folder and then initiate new react-native project using react-native init ProjectName.

Run react-native run-ios / run-android inside your React Native project folder

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You are trying to add react-native in other react project. React Native is like React, but it uses native components instead of web components as building blocks. So install react-native using npm install -g react-native-cli in a new folder and then initiate new react-native project using react-native init ProjectName.

Run react-native run-ios / run-android inside your React Native project folder

Reference