idk about loads, it depends on how everything is setup. Most of this is ajax calls to a backend you control and develop. Making sure the types are coherent between frontend and backend is not a big deal. Generate interfaces based on the types returned by each endpoint.

If it's an external API, do the same thing except it probably needs a more manual approach.

This is not something that's in anyway unique to typescript. The difference is JavaScript is designed to fail gracefully using coercion whereas most other languages and runtimes abort and throw exceptions.