1/ W.r.t. optional parameters, JavaScript having both `undefined` and `null` becomes useful because we can distinguish between a parameter being `null` and it being omitted. (Probably not enough of an upside to outweigh the downsides elsewhere.)
In light of this, I’m wondering if we should try to never explicitly use `undefined`—unless we need to skip a positional parameter:
func(1, undefined, 3)
Often better: named parameters (see link below).
https://exploringjs.com/impatient-js/ch_callables.html#parameter-handling