This is presumably not what you're thinking of but ofc Javascript uses objects as prototype "types". As is, they wont provide what you want, but if there was some kind of "compile-time" processing of prototypes such that types assemblies, dependencies, constraints and other relationships could be manipulated or asserted before they were applied in runtime code, that may provide some of the "first-class type" functionality mentioned.

Ed: actually, Typescript might be a better host for this.