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typescript练习-获取元组长度 #32

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xieyezi opened this issue Aug 18, 2021 · 0 comments

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xieyezi commented Aug 18, 2021 •

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description:

对于给定的元组，您需要创建一个通用的Length，选择元组的长度。

answer:

type Length<T extends any> = T extends {length: number} ? T['length'] : never;

example:

type tesla = ['tesla', 'model 3', 'model X', 'model Y']
type spaceX = ['FALCON 9', 'FALCON HEAVY', 'DRAGON', 'STARSHIP', 'HUMAN SPACEFLIGHT']

type teslaLength = Length<tesla>  // expected 4
type spaceXLength = Length<spaceX> // expected 5

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