You can build an Android app with JavaScript by using the Ionic framework, which leverages several web frameworks to provide a hybrid wrapper over the native Android interface. This allows you to create an Android app without having to write Java or Kotlin code. The Ionic framework supports vanilla JavaScript, Angular, and React, making it a reliable choice for building hybrid Android apps. To generate a QR code, you can use a QR code generation API such as RapidAPI's QRickit QR Code QReator API, which provides a simple and easy-to-use interface for generating customized QR codes. The app uses the HTTPClient class from Angular to make API calls to the QRickit API, which returns the generated QR code image in blob format. The app is built using Ionic Framework with Angular as the base framework.