Can I use JavaScript in React Native?

Setup

By default Expo CLI will use the Metro configuration defined in the @expo/metro-config package (re-exported from expo as expo/metro-config in SDK 41 and greater). You can add custom options for Metro by creating a file named metro. config. js in the project root directory .

React Native CLI has a configuration mechanism that allows changing its behavior and providing additional features. React Native CLI can be configured by creating a react-native. config. js at the root of the project. Depending on the type of a package, the set of valid properties is different.

When using React Native, you’re going to be running your JavaScript code in two environments: In most cases, React Native will use JavaScriptCore, the JavaScript engine that powers Safari .