1. without compiling
2. use expo_ (window npm i -g -expo-cli) send our RN code to our phone, preview immediately!
3. can make code without setups(so many infra structures)
RN does not use web browsers
RN is beatiful translator, interface between us and os(ios, android)
native: listening event. (device가 연결되는 게 앱의 묘미인듯 ㅜㅜ 헉)