TypeScript 2.1 introduced mapped types, a powerful type system feature which allows you to create new types from existing ones by transforming properties.
TypeScript 2.1 introduces the
TypeScript 2.1 adds support for object rest and spread. You can work with rest/spread properties in a type-safe manner and downlevel both features to ES3.
TypeScript 2.1 adds a compiler option for importing helper functions from an external library. The helpers aren't injected into every file, resulting in smaller bundle sizes.