Running a node command in harmony irrespective of OS

Question

So for a *nix machine, it is possible to define a script like so:

scripts: {
  "unit-test": "node --harmony `which jest` --config jest-unit.json"
}

This fails on Windows 10 as the which command is not platform agnostic.

Is there a way to do this as a script that works on both windows AND *nix? And if not, what would the windows script look like?