Is there a way to migrate jsdoc-annotated JavaScript code over to TS, and is TS's minifier as good as Google's closure-compiler yet?
Visual Studio Code has a "Code Fix" that can automatically copies JSDoc into TypeScript annotations. This can be done to an entire file at once.
TypeScript does not come with a minifier. The code it produces is compatible with the target version of JavaScript (e.g. compile ES6 modules into CommonJS) but unminified.
I see. closure-compiler's "advanced" mode takes advantage of jsdoc type info for minifying so I guess generic syntactical minification won't compress as much for the time being.
We (Google TS team) maintain a tool[1] that transforms TS types into jsdoc types for the purpose of feeding them into 'advanced' mode. We also (to answer the grandparent question) maintain a tool[2] that converts Closure-annotated TS into JS. (Why both ways? We transition JS->TS and check it in as the code the user works with, while we use the TS->JS one within the compiler at optimization time.)
[1] https://github.com/angular/tsickle
[2] 'gents', in this repo https://github.com/angular/clutz