[rlt]

TypeScript is definitely statically typed. It is not a 100% “sound” type system, but very few languages actually are (Haskell, Reason, etc)

And in your example of loading data from a server, if you have appropriate lint rules set up your editor and linter will warn you when you pass “any” typed data (such as that returned by fetch’s response.json()) to something expecting another type. You can use something like zod or yup to validate the data is the type you expect before passing it the rest of your typed code, thereby containing possible type errors to a known location where you can gracefully handle it.

This is a problem with any language that accepts typed data from an external system, certainly not unique to TypeScript.