Conditional Types

Conditional Types let you select types dynamically by checking if type T extends type U. They work like ternary conditional operators (T extends U ? X : Y).

Worked example

How it reads

T extends string tests if the generic type extends a string
? 'yes' : 'no' resolves to different types depending on the check

Cloud tip: Conditional types are the core of advanced type manipulation and libraries.

index.ts

TYPESCRIPT

type-checked, then run in your browser

Console

Run your code to see its output here.

YOUR TURN

Write type IsArray<T> = T extends unknown[] ? "array" : "single", declare const kind: IsArray<number[]> = "array", and log it.

Press Run to check your work.

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