Which is weird since they use the isFinite built-in right after that, but I have no idea why they throw in all the string checks and trims and + for type coercion, and then use the global isFinite function which does all that internally. In fact the global function isFinite does everything this package does

(something I just learned tho checking this code out is that there is a global isNaN and isFinite which coerce strings into numbers automatically, and Number.isNaN and Number.isFinite which function similarly but without coercing the string first, so I guess this package exists as a learning aide of all the different ways to ask if something is a number)

EDIT: I now know why they check if a string input is not an empty string, because empty strings get coerced to 0, so isFinite("") returns true.