Mapped Types

Mapped Types build new types by iterating over the keys of an existing type. They map every property of a type to a new type structure, similar to Array.prototype.map() but for type properties.

Worked example

How it reads

[K in keyof T] iterates over all keys K inside type T
T[K] accesses the type of property K in type T

Cloud tip: Mapped types are useful for converting API responses or validation payloads dynamically.

index.ts

TYPESCRIPT

type-checked, then run in your browser

Console

Run your code to see its output here.

YOUR TURN

Write a mapped type Flags<T> that turns every property into a boolean, then const shown: Flags<Pilot> = { name: true, xp: false } and log shown.xp: false.

Press Run to check your work.

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