[williamdclt]

Yeah, in practice I would only encounter the case of arrays being objects when doing something highly polymorphic (eg reading some JSON that can be anything), which likely would have test cases for every type anyway.

But when I’m writing a reusable lib and I can’t perfectly abstract a gotcha, I design the API so that the dev _has_ to make an explicit decision rather than defaulting on their behalf (defaults are evil). So, isObjectOrArray and isObjectNonArray: you have to think about which applies. Another example is sorting: does it sort in-place or immutably? Make it explicit in the function name. Does a function expect a sorted array or will it sort itself? Make it explicit in the function name. And maybe provide both variants.