Quiz · 3 questions

🧙 Generics — Where TypeScript Becomes Itself

Generic functions, types, constraints, defaults, conditional types, infer

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Quiz

01What does function first<T>(arr: T[]): T actually do at the type level?

Hint

Compare with the same function written without generics — you'd lose the link between input and output types.

02What does T extends U mean in a generic constraint?

Hint

Try writing function len<T extends { length: number }>(x: T) { return x.length } and then calling it with strings, arrays, and objects with length.

03What is a conditional type?

Hint

Try type IsString<T> = T extends string ? true : false and see what IsString<'hi'> and IsString<42> evaluate to.

← Previous`infer`: Pulling Types Out of Other Types 🧰 Utility Types — The Built-in Standard Library of Types →`Partial<T>` and `Required<T>`

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