Good that you managed to solve it 
JavaScript bundlers, transpilers, tooling, etc. are indeed really complicated and add quite a bit of cognitive overhead.
Just to add to what I said before, note that defining variables with let or const will not define them as globals on the window object (as opposed to var when used at the top level). In general, if you want a global that you can use from the console, defining it explicitly as window.myGlobal = ... is usually the best way.
