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# TypeScript

## Basic idea

JavaScript plus a structural, gradual static type system (Microsoft, 2012). Compiles to plain JS; types are erased at runtime. The dominant way to write industrial JS today.

## Key facts

* Year / creator: 2012, Microsoft (Hejlsberg).
* Typing: static, structural, gradual (`any` opt-out); generics, unions, intersections, conditional types.
* Compiles to JS — no runtime cost (types erased).
* Notable: discriminated unions, mapped types, template literal types.