TypeScript 常用取法

從值取得型別。

取得陣列中項目的型別

const list = [666, 'bruh', true] as const

type Item = typeof list[number] //  true | "bruh" | 666

// 💡 拆解步驟：
type List = typeof list
type ItemOfList = List[number]

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取得物件裡的值的型別

const myObject = {
  small: 16,
  medium: 20,
  large: 24,
} as const

type Value = typeof myObject[keyof typeof myObject] // 16 | 20 | 24

// 💡 拆解步驟：
type MyObject = typeof myObject
type KeyOfMyObject = keyof MyObject
type ValueOfMyObject = MyObject[KeyOfMyObject]

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