[untog]

Interesting - I wonder whether TypeScript could compile down to this when ES7 is accepted and live in browsers. As it is, I do prefer the syntax of TypeScript.

[jkrems]

Afaik TypeScript is using https://www.npmjs.com/package/reflect-metadata to attach runtime type information, something angular asked them to do (there was no runtime information before). See also: https://github.com/Microsoft/TypeScript/issues/3148

[underwater]

This does runtime checking. Flow and Typescript do static type checking. Which, as long as the systems are sound, means you don't need a runtime component.

[gsnedders]

TypeScript isn't sound, and does rely on runtime checking for a small amount of stuff. I don't know about Flow.