It's open source.
> you can just strip all type annotations with Babel and move on.
Are you implying that this isn't possible with TypeScript?
I think you're vastly misinterpreting what TS is.
It's not anything like CoffeeScript. It's JS plus types and a few other features like Interfaces or advanced ECMAScript features when targetting older versions of the standard.
If you strip away types by exporting to your ECMAScript target of choice, you'll get real JavaScript with the same style as it was written in TypeScript.
It's exactly the same thing you'd get with Flow in that sense. The only additional code you'd get would be for polyfills, but a) those are minimal and b) those will only appear if you export to an older ECMAScript version than the one you wrote it in.
There is no vendor lock.
That's about it though.
If you target ES6 your code may look identical. Even much of the ES5 down leveling produced code that looks like a person wrote it.
I converted a 10k line coffeescript project(with async/await !) to JS and then TypeScript. The similarities are so far apart they might as well be in different dimensions. But, if you don't want to take a rando posters word for it, it's pretty easy to make a little sample project and see if the output is to your liking.
The same can be done to it that would be done to Flow: you can just either strip types manually, or just do a single export to your ECMAScripttarget of choice. It'll be native JavaScript. Even the little shims/polyfills it does (to support older ECMAScript versions if you wish to export to it) are optional and can be disabled.
https://github.com/Microsoft/TypeScript/wiki/JSDoc-support-i...
It does a decent enough job at return types, but not a whole lot beyond that.
function double(x) {
return x * 2;
}
const result = double("foo");