JSDoc

• https://github.com/Microsoft/TypeScript/wiki/JsDoc-support-in-JavaScript
• webpack's codebase uses JSDoc with linting by TS https://twitter.com/TheLarkInn/status/984479953927327744 (some crazy hack: https://twitter.com/thelarkinn/status/996475530944823296)
• JSDoc can type check if using closure-compiler https://github.com/google/closure-compiler/wiki/Types-in-the-Closure-Type-System

Problems to be aware of:

• object is converted to any for some reason.
• If you have an error in the jsdoc, you get no warning/error. TS just silently doesn't type annotate the function.
• casting can be verbose

(thanks Gil Tayar and Gleb Bahmutov for sharing above commentary)