But I would love runtime checks for types. Even if that was a compiler step I could flag on—but that makes it a great deal more complex both to implement and reason about, likely—without starting fresh anyway.
IMO, runtime type analysis is a code smell. There are few scenarios where the simpler and more efficient solution involves querying type metadata at runtime. Particularly in a language that directly supports dynamic dispatch, you should think hard before adding anything resembling an "if typeof(mything)" check.
(Reading through the thread, there’s apparently some libraries that can do this; I’ll have to try them out next time I need this.)
const shout = (message: string) => console.log(message)
into something like
const assert = require('assert'); const shout = (message) => { assert(typeof message === "string"); console.log(message); }
of course this doesn't work for more complicated types