This is not unavoidable in typescript at all. It really depends a lot on how you have structured your application, but it's basically standard practice at this point to use e.g. zod or similar to parse data at the boundaries. You may have to be careful here (remember to use zod's .strict, for example), but it's absolute not unavoidable.

I should have been clear. Yes it is avoidable but only by adding more checking machinery. The bare language doesnt help.

In Go etc. If a struct doesn't a field foo then there will not be a field foo at runtime. In JS there might be. Unless you bring in libraries to help prevent it.

You are relying on someone remembering to use zod on every fetch