The TypeScript team recently announced version 3.1 of TypeScript, adding mappable tuple and array types and several other refinements.

When classes are more structure than you need, tuples let you specify simple type-safe aggregates of other data types. They'll also let you create a dictionary collection…but it won't be type-safe. In ...

Next TypeScript release, due February 25, will support a limited form of checking against conditional and indexed acces types in return statements.