Moreover, aside from namespaces and enums (which are discouraged), none of those features were incorporated into TypeScript until they were on track for inclusion into JS. They weren't taken from TypeScript and imported into JS; TypeScript took them from the ECMAScript people.
Being able to compile TypeScript by just stripping types has become a design principle of the language. For better or for worse, the TypeScript team steadfastly refuses to try to innovate on runtime language features at this point.
