You mean like Typescript, an add-on that transpiles to Javascript?

I'm sure they meant an actual statically typed language. I agree that dynamic languages are fun and productive ... until the codebase becomes big and complex, and then not knowing what shape any data is quickly becomes a nightmare to understand and debug.

> not knowing what shape any data is quickly becomes a nightmare to understand and debug

I remember when I experienced exactly this, it kind of flipped switch in my head which made me love static typing.

RBS comes by default with Ruby, Sorbet is 3rd party.