This proposal is brand new (stage 0), but I hear that a lot of work has been put into it behind the scenes by a lot of people, so it has that going for it…

This proposal aims to enable developers to add type annotations to their JavaScript code, allowing those annotations to be checked by a type checker that is external to JavaScript. At runtime, a JavaScript engine ignores them, treating the types as comments.

The aim of this proposal is to enable developers to run programs written in TypeScript, Flow, and other static typing supersets of JavaScript without any need for transpilation, if they stick within a certain reasonably large subset of the language.

The implications of this change are pretty massive, if it were to ever ship. And you better believe we’re putting together a JS Party episode to discuss it with the people involved.