Yes this has been a lifesaver. We have a nodejs application without a lot of obvious structure and lots of ad-hoc objects thrown around. Gradually adding .d.ts

Yes this has been a lifesaver. We have a nodejs application without a lot of obvious structure and lots of ad-hoc objects thrown around. Gradually adding .d.ts files, adding tsdoc comments (`@param {SomeType} foo`), and running `tsc` at test-time has already caught numerous bugs that otherwise would have required lots of unpleasant time with the debugger. We just mandated that all new code get written in typescript (we transitioned everything to run via `ts-node` before actually using any typescript and it was super painless). Any "significant" changes to existing code (>= 10 lines diff usually) must either first convert the code to TS or add types via tsdoc. This is a "first step" PR that lets us confidently make changes in subsequent PRs after type info is there to help. Forces us to pay down tech-debt in a real way that has immediate payback.