Is typescript useful?

Question

Do you use it in your apps? What if your app is pure JS?

Answer 1

typescript is generally only used in large scale projects. It's heavily used if you're working with the angular web framework but otherwise you probably wont need it.
It compiles into pure javascript so you can accomplish things without it but check it out and see if any of the features are necessary for what you need

Answer 2

You should write typescript whenever you can, it makes javascript more bug free, and easier to form documentation without tool like jsdoc.