Structural typing, generics, narrowing, utility types, and typing component contracts.
3 questions in Frontend Engineering.
A TypeScript exhaustive switch uses a discriminated union and a never check so the compiler fails when a new variant is added but not handled. This turns future union growth into a compile-time error. It also connects discriminated unions to the point an interviewer is testing.
A safe TypeScript component props API models legal states with discriminated unions, ties related props together with generics and keeps any out of the public surface.
TypeScript stops protecting you at runtime boundaries such as JSON, HTTP requests, local storage and third-party packages. Validate untrusted input at the boundary, then let static types carry the trusted shape inside the app. It also connects type soundness to the point an interviewer is testing.