Question 1

What is a branded/nominal type pattern?

Accepted Answer

Intersect with unique brand to prevent mixing compatible primitives (UserId vs OrderId). Zero-runtime cost with casting at boundaries. Improves domain safety.

Question 2

Template literal types — uses?

Accepted Answer

Compose string unions like on${Capitalize<Event>} for typed event names. Powerful for routing paths and CSS-in-TS. Keep complexity bounded.

Question 3

What are recursive types good for?

Accepted Answer

JSON, trees, linked structures — types referencing themselves. Need base cases. Compiler depth limits exist — simplify when errors obscure.

Question 4

Satisfies operator — why use it?

Accepted Answer

Checks a value matches a type without widening to that type. Preserves literal inference while validating shape — great for config objects.

Question 5

const type parameters?

Accepted Answer

generic const T preserves literal types from arguments. Helps APIs that want narrow inference from object/array literals.

Question 6

Polymorphic this types?

Accepted Answer

Methods return this for fluent subclass-preserving builders. Useful in base classes with fluent APIs.

Question 7

When is type-level programming too much?

Accepted Answer

When errors become unreadable and juniors can't contribute — prefer simpler models. Balance cleverness with DX. Document complex types heavily.

Advanced Types TypeScript Interview Questions

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