NativeScript easily supports TypeScript. In fact, the core of NativeScript is developed using TypeScript. The team feels the strongly typed environment helps to move error catching to a compile time event, rather than slipping in as a run time event. In the end, less bugs make it to production and that is a Good Thingtm. Also, our development teams use modern features like async/await and other ES7-level goodies without having to wait for ES7 platforms to mature.
For those who like to follow along closely, Alex also wrote a very detailed step by step companion guide to "Hello World native iOS mobile app using TypeScript and NativeScript
" for those that prefer to read, rather than watch videos.
If you like these sorts of videos, stay tuned to Alexander Ziskind's YouTube Channel