All of these are cause JS builtins like to auto-cast things. + only accepts strings or numbers, - only accepts numbers. Really these should be errors instead, b

All of these are cause JS builtins like to auto-cast things. + only accepts strings or numbers, - only accepts numbers. Really these should be errors instead, but it's also not very surprising or annoying once you know this. Basically, don't perform arithmetic on things that aren't numbers. The name parseInt suggests it takes a string. Especially "" - 5, why?