The maybe too subtle point I was trying to make is that, even though the TypeChecker object literally provides an EmitResolver (I think? something like that?), in terms of the conceptual layout of the compiler, if you have a box labelled "Type Checker" it's natural for the reader to think it's where type checking happens.

In other words, the graph is something like

    TypeChecker object -> EmitResolver -> js files
      |
      v
     type checking