This document discusses using Firebase and NativeScript to build mobile apps with a single JavaScript codebase. NativeScript allows building native iOS and Android apps with JavaScript by providing direct access to native APIs and UI elements. It can be used with or without Angular 2. Firebase provides backend services like realtime database, analytics, authentication and remote config that can be easily integrated into NativeScript apps. A demo is shown of building a simple Twitter-like app with NativeScript and Firebase.