Quiz · 3 questions

🪄 Type Manipulation — Computing Types from Types

keyof, typeof, indexed access, mapped types, template literals, advanced infer

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01What does keyof { id: number; name: string } give you?

Hint

Hover keyof User in your editor — TypeScript shows you the literal union.

02What's the difference between keyof T and T[keyof T]?

Hint

Try writing both on an interface in your editor and hovering each to see what comes out.

03What does a mapped type { [K in keyof T]: ... } actually do?

Hint

Compare { [K in keyof T]: T[K] } (identity) with { [K in keyof T]?: T[K] } (Partial) — only one character difference, very different result.

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