[buu700]

TypeScript itself doesn't really add new language features; it just tracks the ECMAScript spec and considers proposed features for implementation after they hit stage 3.

The enhancements coming out in new TypeScript releases are largely related to typing expressiveness / type inference precision (covering more edge cases where one might have previously resorted to `any`) and strictness (catching more errors at compile time).

[jsheard]

Indeed, the only Typescript feature I can think of that isn't purely for type checking or lifted from ECMAScript is Enums, and Enums have been around forever.

[camus2]

Well it has supports for JSX and decorators which AFAIK aren't in the spec yet. It also has a syntax for class mixins without actually doing any desugaring when the code is transpiled. So it's not quite just JS + types.

[jsheard]

Ah, I forgot about those. Nonetheless JSX and Decorators were added to the language back in 2015, so they've been sticking strictly to ECMA features for nearly 3 years now.

[namelost]

It has public, private and protected members (checked at compile-time), which is a bit of a mess because ES is gaining an independent notion of private fields (checked at runtime).