type-narrowing

Type narrowing refines broad union and nullable types based on control flow, reducing unnecessary type assertions and preventing runtime errors. It applies to code dealing with Type | null, Type | undefined, string | number, and discriminated unions.

Type guards discriminate between alternatives in discriminated unions via kind-based switches. You can also use typeof and instanceof guards to narrow types down to a specific variant, ensuring runtime safety.

Null checks and throw or return early patterns guarantee narrowed types after the guard. This control flow mechanism lets TypeScript infer the precise type, safely handling falsy values and Type | undefined scenarios.

Yes, user-defined type guards extend narrowing to support standard narrowing patterns. You can apply them in a function that handles union or nullable values to let TypeScript infer the precise type.

Yes, the in operator performs property presence checks for type narrowing. Apply it to code dealing with union types to refine broad types based on control flow and improve type safety.

Type narrowing is required for nullable types to refine broad Type | null unions based on control flow. This reduces unnecessary type assertions and prevents runtime errors when handling falsy values.