Earlier quoted context omitted.
jsonriver's invariants do give you enough info to notice which values are and aren't complete. They also mean that you can mutate the objects and arrays it returns to drop data that you don't care about. There might be room for some helper functions in something like a 'jsonriver/helpers.js' module. I'll poke around at it.
Please consider it a feature request
For anyone else following along, see https://github.com/rictic/jsonriver/issues/39