CodeHS also uses Expo for mobile apps. Expo is a collection of tools that lets you do even more with React Native apps. Expo lets you easily access parts of your phone's functionality like the camera and contacts list, and also provides components that React Native alone doesn't have, like icons and vector drawings. More info about Expo is available in the Expo Documentation. On CodeHS, when you create a React Native program, you can access the functionality of both React Native and Expo.
Expo also has its own app, which we encourage you to use to view your React Native programs and graphics programs on mobile by scanning the QR code provided in the CodeHS editor from the Expo App.