At least in the node.js native TS implementation, they strip the types and don’t do checks, so you don’t get runtime type checks:

Node.js does not type check your code when it runs TypeScript files. Use the TypeScript compiler separately if you want to catch type-related errors:

nodejs.org/learn/typescript/run-natively

I think, but I’m no expert, but in order to have type checking you need to have some kind of compilation check? You cant just start interpreting and hope to work things out on the fly?