Thanks for the explanation. > If you upgrade your function from no second argument to a numeric second argument [...] It will not crash, because it still perfe

Thanks for the explanation. > If you upgrade your function from no second argument to a numeric second argument [...] It will not crash, because it still perfectly type-safe It's type-safe using a definition of "type-safe" that is defined relative to the underlying JavaScript model of "corrupt the user's data rather than crash". It wouldn't be type-safe using most other languages' (including Python, for example) model of "functions have a type that includes the number of arguments, and applying them to the wrong number of arguments is meaningless and hence not considered type-safe". It's fair for TypeScript to use this approach. But it is surprising to many of us, who view type systems as tools for ruling out some dumb functional bugs, not just crashes.