What are unknown, any and never?

Definition:

any allows operations without normal type checking, while unknown accepts any value but requires checks before use. never represents a situation where no value is possible, such as the result of a function that always throws. These types describe different levels of knowledge and should not be used interchangeably.

Key points:

• unknown: check the value before using it.

• any: skips type checks and can hide bugs.

• never: no possible value; useful for exhaustive checks or functions that always throw.

• Use unknown for external data until you have checked its structure.

• Use never in exhaustive switch checks so a newly added union case causes a compile-time error.

Interview point:

• unknown keeps the burden of proof on the code using the value; any removes that protection.