To be honest I struggle with the frustration of programmers of dynamic languages building their own (mostly half-assed) type checkers, after years and years of

To be honest I struggle with the frustration of programmers of dynamic languages building their own (mostly half-assed) type checkers, after years and years of dealing with their bogus arguments about why dynamic languages are superior and all you need is unit tests (the same cohort is also now on a misguided crusade against unit tests but that's a whole other story). At least the JS crowd had the decency to buy into a whole new (far better) language instead of a bolt-on solution.