Google did a bit of work on converting Closure annotated JavaScript to TypeScript. It's called Gents and it's part of the Clutz project https://github.com/angul

Google did a bit of work on converting Closure annotated JavaScript to TypeScript. It's called Gents and it's part of the Clutz project https://github.com/angular/clutz/tree/master/src/main/java/com/google/javascript/gents https://github.com/angular/clutz/tree/master/src/main/java/c... We used it at Lucid when we converted our codebase from Closure annotated JavaScript to TypeScript. https://www.lucidchart.com/techblog/2017/11/16/converting-600k-lines-to-typescript-in-72-hours/ https://www.lucidchart.com/techblog/2017/11/16/converting-60... Google has support for using TypeScript in Closure annotated JavaScript via Clutz: https://github.com/angular/tsickle https://github.com/angular/tsickle It also has support converting TypeScript to Closure annotated JavaScript via tsickle: https://github.com/angular/clutz https://github.com/angular/clutz Before we converted all of our codebase to TypeScript we used both Clutz and tsickle. It was complicated to setup, but it worked. Now we just use tsickle. It's great to get the optimization of the Closure Compiler while using TypeScript.