If you are using ExtJS on a regular basis, then you may want to take a look at the work done by Gareth Smith, Fabio Parra dos Santos, and their team at https://github.com/fabioparra/TypeScript. This project is a fork of the TypeScript compiler that will emit ExtJS classes from standard TypeScript classes. Using this version of the compiler turns the tables on normal ExtJS development, allowing for natural TypeScript class syntax, the use of inheritance via the extends keyword, as well as natural module naming, without the need for magic strings. The work done by this team shows that because the TypeScript compiler is open source, it can be extended and modified to emit JavaScript in a specific way, or to target a specific library. Hats off to Gareth, Fabio, and their team for their ground-breaking work in this area.