Is TypeScript a bad idea? I think not, because it adds the syntactic sugar needed to concentrate on the app-logic and takes away the clutter needed for OO/modularization . Take a look to other languages: the language Objective-C extends the C programming language to object-oriented programming language, but it is C-code. Or take a look to C++. It adds object oriented features to the C programming language, so it can include C-code.
And then there are other features such a type-checking, refactoring, etc. which TypeScript enables since the code contains type information.