[lolinder]

> Assume an SPA and the response of an API call was typed with CountryCode in some field, then somebody just worked on the API - I prefer to crash my world close to were my assumption doesn't fit anymore, but YMMW.

Agreed on crashing, but I prefer to push validation to the boundaries of my process and let the type checker prove that all code within my process is well-typed.

Defensive programming deep in my code for errors that the type checker is designed to prevent feels wasteful to me, both of CPU cycles and programmer thought cycles. Type errors within a process can only occur if you abuse TypeScript escape hatches or blindly trust external data. So don't cast unless you've checked first, and check your type assumptions about data from untrusted APIs before you assign it to a variable of a given type.