What does the following type guard pattern enable that ‘as’ casting does not? function isUser(value: unknown): value is User { return typeof value === ‘object’ && value !== null && ‘id’ in value; }

Question

TypeScript Professional — Hard

What does the following type guard pattern enable that ‘as’ casting does not? function isUser(value: unknown): value is User { return typeof value === ‘object’ && value !== null && ‘id’ in value; }

Accepted Answer

The type guard pattern in the function isUser allows TypeScript to verify and narrow the type of a value at runtime, integrating actual validation with the type system. This enables TypeScript to trust the type only when the function returns true, ensuring more reliable type checking.