Typeof

An in-depth guide to the typeof operator in Type Space. Learn the distinction between Value Space and Type Space, reverse-engineering types from runtime objects and functions, combining keyof typeof, and deriving single-source-of-truth types.

Understand how TypeScript’s Control Flow Analysis engine refines types across code branches. Master typeof guards (and the typeof null quirk), instanceof class narrowing, the ‘in’ property operator, equality narrowing, and truthiness pitfalls.